yacht design rules

Understanding the IOR Rating System & Formula

August 25th, 2017
Yachtmaster

Although the magazines and marinas are full of flat designed, chined and wide-sterned modern yachts made to perform and host large volumes, a great number of yachts nowadays have their origins in the Seventies and Eighties as we call them “Classic GRP Yachts”. As I was roaming the jetties of my home marina I came to rest in front of such a very, very nice and well kept yacht: A German made Hanseat in blue.

She bears the distinctive shape of a whole class of yachts which defined the Seventies yacht design: The IOR-yachts. IOR? Most of you may know this fictional conversation very well by their own neighbours in the berth: “Ah, this is a nice, classic boat indeed!”, “Yes, I like her. Her lines. She´s an IOR-yacht!”, “Yeah, for sure!”. IOR. We are all too familiar with the wide bulky hull shaped like a tea kettle. But what does IOR really mean? Here´s a short but hopefully clear explanation.

History of the IOR-Rating System

First of all, IOR, the “International Offshore Rule”, was a rating system introduced in the Sixties when for the first time in history regatta-rules and handicap ratings of Europe (namely of the Royal Ocean Racing Club of England, RORC) and America (to be precise of the CCA, the Cruising Club of America) sought to standardize their set of rules to ensure a worldwide rating system for sailing yacht races. The IOR has been kept in place up until the early Eighties when it was superseded by the more technical and scientific advanced IMS and IRC-rating, which are in place still today.

The set of rules changed massively during the years as their trustees tried to keep up with the pace of yacht designers and boat builders who sought to interpret the rules in such a way that thy would make the fastest boats possible within this set of rules. In such an environment, as we all know from other occasions, the mind of the people does incredible things and so the IOR set of rules sparked a whole generation of naval architects to create yachts and hull shapes within this set of rules – leading to this one, very iconic feature of IOR-yachts: The tea kettle shape of the hull. But what´s to it?

Design Features of Sailing Yachts under IOR-Rating

Well, in short, the IOR called for short waterline lengths. It favoured yachts with a short waterline and penalized longer boats. But as we all know: The longer the waterline length, the fast the boat sails. By the same time, naval architects and designers of the boats tried to keep the wetted surface of the yacht as small as possible, shortening the surface area of both hull, keel and rudder blades.

The yachts had been fitted with a sharp bow and the distinct “cruiser stern” which bears a large overhang. Now, let´s cast off and get the sails hoisted. What happens? First of all, when the IOR-shaped boat is now sailing, it will start to heel to leeward as expected. Due to the unique wide girth, the “tea kettle”-hull will now immerse into the water. As you may imagine by looking at such a tea kettle-shaped hull, due to the unique design features of the IOR-shaped hull, the length of the waterline increases greatly thus “imposing” a larger hull and increasing speed. That´s the theory.

Implications of IOR-designed Hulls

It really worked well for a number of yachts and IOR proved to be the offshore rule setting off a huge wave of new yachts to be built and new races to be raced. But the IOR-yachts had also some unwanted implications and sailing characteristics which are nowadays considered frowned upon the least if not to say dangerous.

First of all, IOR-yachts are a kind of unstable boats in terms of seakindness. Due to the round chined hull and the wide girth, those boats are sailing massively heeled and are always in heavy motion even in lighter swell. Modern yachts with wider sterns and pronounced chines are heeling up to a certain point and will then sail very stable. Also, during the catastrophic events of the iconic Fastnet Race of 1979 more of those unwanted and possibly dangerous effects of IOR-constructions emerged in a way that the formula itself, its official role in regulating races and the design features had been abandoned by both the commissions as well as by the naval architects. If you want to dive deeper into this topic, there are numerous books and websites available.

In present naval design of yachts the IOR-inspired hull shapes have completely vanished. Although IOR-yachts have undeniable qualities in sailing hard upwind, they are nowadays considered too shaky in terms of sailing characteristics. Also, the somewhat narrow aft sections of these yachts do only leave space for quarter berths the best – best example here is the Beneteau FIRST 30 on which I did have the pleasure to make a 7-day-short dash to the Island of Bornholm (read the full articles here and here ). This yacht offered way more comfort and volume on 30 feet than my 33 feet IOR-era King´s Cruiser 33.

So in the end, the IOR-era was an attempt to flatten the worldwide rating systems to pave the way for a global racing circus. Designers reached out far to squeeze out the best designs possible. In a way the IOR proved that a bright mind can create miracles even inside the narrowest borders. But IOR also proved that too many rules can have limitations and even dangerous aspects as well. I personally admire some of the IOR-era designs, such as my own boat – but I also praise the technological advance that brought us faster, safer and beautiful designs as well.

Other interesting articles on that topic:

What´s the Yardstick rating system all about?

Tim Kroeger on racing the Swan 60 .

Sailing a Pogo 40 Racing Yacht.

Hull Design – Basic Rules to Follow

When you look at a boat, you have to remember that the hull is one of the most important parts . If you have a poor design the boat will not be stable, will not float or could lean to one side.

The boat hull acts as a balancer for your boat so there are a few rules to make sure you follow when designing and creating one.

Hulls should be simple yet very strong.

If you are inexperienced it would be better to design and build a hull that is simple, however you still have to be mindful of both the strength and weight.

The design should have the center of buoyancy fixed some where about halfway between the stern and bows. John Teale a well known author various boating books, had said “Whatever you do with the hull, make sure that it keeps the buoyant center at the right point. This will ensure that your boat doesnâ€™t topple over or get un-balanced easily by waves.”

Curving: When you are designing the wall sided type of boat, always make sure that the degree of curving that you are incorporating at the sides of the boat is equal to the curvature of the base of the boat. This way, the pressure of water will be equal on all parts of the boat. This essentially means that your boat will be streamlined and perfect for smooth, jerk reduced movement.

Building boat hulls is not a big headache but these basic points have to be kept in mind if you want a perfect streamlined hull. Say you are designing a ballasted boat; make sure that the weight of the boat (the up-weight) is always forty to fifty percent greater than the weight of the ballast.

The best would be if you could design boat hulls that will hold the ballast below the waterline at all times. So, boat hulls being the most important part of a boat, require the greatest attention and therefore pay heed to what type of hull you are building if you want a good boat.

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UNDERSTANDING THE DIFFERENT BRANCHES OF BOAT DESIGN

Boat design is a collaborative effort, requiring the expertise of professionals from various fields to create functional, aesthetically pleasing, and seaworthy vessels. In this article, we’ll explore the key branches of boat design, shedding light on their roles and significance.

Exterior Styling

Exterior styling focuses on a boat’s outer appearance, shaping its lines, proportions, and overall visual appeal. Designers strive to create distinctive and attractive looks that enhance the vessel’s marketability and reflect the owner’s taste and preferences.

Interior Styling

Interior styling is concerned with the aesthetics, functionality, and comfort of a boat’s living spaces. Designers take into account factors like ergonomics, material selection, lighting, and color schemes to craft inviting, practical, and visually appealing interiors that elevate the boating experience.

2D Drafting

2D Drafting is useful in boat design for creating detailed technical drawings and blueprints that bring the designers’ concepts to life. These drawings accurately represent the vessel’s dimensions, structure, and systems, serving as a guide for builders during the construction process.

Naval Architecture

As the backbone of boat design, naval architecture focuses on the overall form, structure, and performance of a vessel. Naval architects consider factors like structural strength, stability, hydrodynamics, and weight distribution to create efficient, safe, and seaworthy boats while ensuring compliance with industry regulations and standards.

Marine Engineering

Marine engineering addresses the mechanical systems of a boat, involving material selection, propulsion system design, and efficient fuel and power systems. They collaborate with naval architects to ensure the seamless integration of a boat’s structure and systems.

Electrical and Electronic Systems Design

This discipline is dedicated to the design and integration of electrical and electronic systems within a boat. Designers work on wiring, power distribution, navigation, communication, and entertainment systems, ensuring their efficient, reliable, and safe operation while meeting the vessel’s energy requirements.

Rigging and Sail Plan Design

For sailboats, rigging and sail plan design is a critical components of the overall design process. Designers calculate the optimal sail area, mast height, and rigging configuration to achieve the desired performance and handling characteristics. This discipline demands a deep understanding of aerodynamics, material properties, and sailing techniques.

Statutory Compliance

Ensuring safety and compliance is crucial in boat design, as vessels must adhere to international and local regulations. Designers consider structural integrity, emergency systems, life-saving equipment, fire protection and while ensuring that boats comply with various classification societies’ rules and maritime laws.

Material Science

Innovations in materials play a significant role in boat design. Material science involves selecting the best materials for a vessel’s hull, deck, and structural components based on strength, weight, durability, and cost. Designers must understand the properties and performance of materials such as composites, metals, and plastics to create durable and efficient boats.

Fluid Mechanics/CFD

Understanding fluid mechanics is essential for designing efficient and stable boats. This discipline focuses on the interaction between water and the vessel, analyzing aspects like resistance, propulsion, and maneuverability. Naval architects use this knowledge to optimize hull shapes, keel designs, and rudder configurations, ultimately enhancing the boat’s performance and fuel efficiency.

Rendering / Animation

Rendering and animation play a vital role in the boat design process by bringing concepts to life through visually stunning, accurate, and detailed 3D models. These digital representations enable designers to showcase their ideas to clients and stakeholders, facilitating communication and decision-making during the design process.

In conclusion, the complete design of boats involves different branches of boat design, each contributing to the vessel’s functionality, aesthetics, and performance. These disciplines must work together effectively to create boats that not only cater to the needs of their owners but also comply with industry regulations and standards. By understanding the roles and interdependencies of these disciplines, aspiring boat designers can better prepare themselves for a successful career in this exciting and dynamic field. Embracing the challenges and rewards that come with mastering each of these disciplines will pave the way for the creation of innovative, functional, and visually appealing vessels that push the boundaries of the boating industry.

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The J Class

J Class yachts were originally built to the specifications of the Universal Rule. The J Class really represents the golden age of racing for the America’s Cup in the 1930s when this Universal Rule was used as the determining measurement system.

About the Class

Designers had to produce a J Class yacht which had a rating of between 65 and 76 feet. That was not the length of the boats but a product of the limiting factors of the rule’s equation. Any of the determining factors such as length, displacement or sail area could be changed but such changes required proportionate change in other factors to compensate. This allowed them to be raced on a level basis. Stability was not taken into account. Limits were set on measurements for waterline length, draft, freeboard and so on.

The three original surviving Js - Velsheda, Shamrock and Endeavour - have been refitted for worldwide cruising and racing. Their displacements have increased and the yachts no longer rate as a J under the Universal Rule definition, with the exception of Shamrock V, which was the smallest of the Js.

In total nine J Class yachts are active now with six replicas having been built since 2003; Ranger, Rainbow, Hanuman, Lionheart, Topaz and Svea.

The J Class Association

The J Class Association (JCA) was founded to protect the interests of the Class, present and future. Among its responsibilities it monitors and agrees the veracity of designs to which new replica boats can be built to, the build materials and specifications, which since Hanuman and Lionheart have included aluminium alloy.

It’s objective is to keep the J Class fleet and races alive and to encourage new build yachts (replica builds from original plans) to join the Class. The intent is to race the surviving Js, new existing Js, and potential new replica Js together in such a manner that has a fair handicap, to ensure that.

The Rules are kept as short and simple as possible, in order to meet the objectives. The Rules are written in the proper gentleman’s spirit, not to be bypassed to gain advantage, which is not in the spirit of the Class.

The original late 20th Century refits of the three surviving Js were used to help respect the tradition and guide the structure of these rules.

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Class rules

Built using composite materials, IMOCA monohulls are designed to be as light as possible to favour speed, whilst also being fairly solid to withstand the worst possible conditions when racing on the open sea, particularly during the Vendée Globe.

Main criteria for the IMOCA class

30 YEARS OF TECHNICAL INNOVATIONS

These 60-footers really came into being in 1986, during the second edition of the BOC Challenge where five monohulls were reasonably proportioned at 18.28 metres (60 feet). Even back then, the most modern monohulls were already displaying the characteristics of boats designed for the downwind conditions of the Southern Ocean, namely a wide beam and a long waterline.

A few years later, in 1998, canting keels designed to increase the righting moment became the norm and computer systems became increasingly important for retrieving weather forecasts and communicating with land. Essential for singlehanded sailing, autopilots also gradually became more and more 'intelligent'. Hulls and sail plans have also evolved, with boats becoming more powerful and featuring wider sterns and improved performance upwind. Cockpits have also become increasingly well protected, some boats even sporting sliding roof cuddies to protect the manoeuvring area.

The safety requirements imposed by the IMOCA class on both sailors and naval architects have contributed a great deal to the boat’s success. Since 2000, these monohulls have had to prove before a race start that they’re able to right themselves without outside assistance and guarantee they are watertight inside as well as extremely buoyant in the event of capsizing or water ingress. With a minimum of twenty boats at the start of the Vendée Globe since 2000, today IMOCA is the biggest offshore class in the world. Consequently, the history of IMOCA and that of the Vendée Globe are one and the same. Midway through the noughties, foils put in an appearance on the America's Cup multihulls and then very quickly began to grace some of the IMOCA monohulls. These lifting surfaces shaped like Dali moustaches enable the boat to 'plane', skimming over the surface of the water and thus limiting the water resistance and enabling the boat to accelerate quickly. Six foilers took the start of the Vendée Globe 2016-17 (Banque Populiare VIII, Edmond de Rothschild, Hugo Boss, No Way Back, Safran, St-Michel-Virbac and Maître CoQ), two were forced to retire but the four ranked boats topped the final leader board headed by the winner and course record holder, Armel Le Cléac'h (74d 3h 35m 46s).

Since then, the class has opened up the measurement regarding how to trim the foils. As such, they have greater freedom of movement (up and down & fore and aft), stimulating the architects’ creativity all the more. For the Vendée Globe 2020-21, eight new boats will be at the start, all equipped with the latest state-of-the-art foils. Observers believe that the event record might well be beaten by several days… making a circumnavigation of the globe in under 70 days a distinct possibility. From 2021-22, this story will be shared with that of The Ocean Race, a crewed round the world race with stopovers.

ACCESS THE LIST OF OFFICIAL DOCUMENTS Contact the class: [email protected]

Iridium Certus® and Thales VesseLINK: Keeping the Vendée Globe fleet connected and safe

The IMOCA fleet taking on the challenge of the Vendée Globe solo round-the-world race has been fitted with a state-of-the-art satellite communications system, comprised of the Thales VesseLINK and the Iridium Certus serv…

The IMOCA general meeting has chosen the way forward with a full race programme for the 2021-2025 cy…

The IMOCA Class meeting marking the end of the summer holidays was held on Thursday 27th August using virtual technology. This meeting enabled the members of the Class to carry out an early appraisal of what has happened…

Alex Thomson: “The boat is going good”

The word from the English south coast is that the skipper of the latest and most radical HUGO BOSS, is feeling very confident about his programme and his boat leading up to the Vendée Globe.

Charlie Enright: The new Ocean Race calendar gives us more time to make the right choices

Charlie Enright, the co-skipper of 11th Hour Racing, believes the new schedule for The Ocean Race – with the next race due to start in October 2022 – will give his team and rival IMOCA entrants more time to make the best…

Messing about in boats since 1975. Online Since 1997.

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Creating A New Yacht Design Copyright 2016 Michael Kasten Updated June 2016 The Yacht Design Process The following article is a summary of how a new custom yacht design is imagined, sketched and drawn. In addition to the following notes, our Introduction web page provides an outline of our general approach to yacht design. While seemingly complex, the design process is made up of a series of incremental steps, much like the building process itself. The goal of undertaking the design of any new yacht is to take a unique set of owner requirements and to turn them into the best possible solution to those requests. If the resulting design is to be what it should be, each of the steps outlined below must be addressed thoroughly. There is first the idea, and then the bringing forth of the idea into a functioning reality. In order to get the relevant information on the table, two primary ingredients are necessary: I. Owner's Specification: The first 'design task' is actually performed by the prospective boat owner. It is first to imagine the goal, and then to create an 'Owner's Specification' or 'mission statement' for the proposed vessel. With that information understood, we will provide a written Design Proposal to outline how we propose to meet the goals that have been set forth. Rather than being a detailed description of the result of the design process, the Owner's Specification is better if seen as a general guide to the intent of the design. Toward that end, ideally the owner's 'mission statement' will be kept fairly simple, since the details of the design will emerge as a result of the design process itself. The basic information needed is an outline of the intended vessel's size, layout, materials of construction, the intended use, range, speed, rig, and general aesthetic. The essential information should include the intended schedule for designing and building the yacht. II. Design Proposal: My first job is to understand the preliminary Owner's Specification, then to provide the prospective client with a detailed outline for creating the new design. This is in the form of our standard written 'Design Proposal' which includes the following: A written outline of the design process itself. A list of the deliverable drawings and documents. An estimate for the design work required in order to create the design and to detail the plans for the vessel as described. The following paragraphs describe our design process, and outline the deliverable drawings and documents. Stage I - The Preliminary Design Study After our ' Design Proposal ' has been reviewed, if the prospective boat owner approves of what we have proposed, then the actual design work can begin. A custom design starts with listening to the requirements of my clients. The objective is to create the best mutual design solution in terms of vessel type, layout, size and style. My goal is to propose an appropriate form and function to suit the vessel's intended purpose, and to follow that up with a thorough analysis of structure, stability and performance. There will first be a series of information exchanges, possibly including clippings of similar vessels or sketched layouts provided by the client. After the owner's requirements have been articulated I will usually begin by creating a preliminary 3D CAD model of the intended vessel, which is most often created by adapting one or more of our existing designs or prototype designs to its new purpose. The 3D model allows us to determine: The envelope available for the accommodations The overall size and hull form The preliminary internal structure (bulkheads and soles) The rig (if for a sailing vessel or motor sailor) The styling and features of the superstructure The preliminary hydrostatics With that, I will prepare a few CAD generated drawings in order to show the proposed layout in Plan and Profile views and a perspective view of the proposed Exterior Styling . Combined with a description of the proposed dimensions and other particulars of the vessel, this is the beginning of what I refer to as 'Stage I' or the preliminary ' Design Study .' Stage I is basically a process of ‘discovery’ wherein we mutually discover the best solution to your requests. In pursuit of that ‘discovery’ process we will review our proposed design solutions against the original specification -- or possibly the initial specification will be revised according to what we discover. This process is both flexible and adaptable. During Stage I we will strive to establish the accommodations, styling, size, dimensions, and the target displacement. Our goal here is to provide a "proof of concept" for the design so that further changes can be kept to a minimum. When the preliminary design has been approved by the owner, Stage II can begin. Stage II - The Estimating Plans The goal of Stage II is to create the first few sheets of the actual Building Plans, and to generate a number of essential documents that will be required by builders so that an accurate construction estimate can be provided. The first part of Stage II involves finalizing 'Stage I Study Drawings'. The preliminary Estimating Plans will therefore include: The proposed Sail Plan or Outboard Profile The proposed Interior Profile and Arrangement Plan Once those drawings have been approved, we can proceed knowing that further changes will be minimized. When completed, the Estimating Plans Package will include: Sail Plan / Outboard Profile Interior Profile and Arrangement Plan Structural Profile and Arrangement Plan Equipment List Vessel Specification Painting Specification Preliminary Weight Study Preliminary Power and Range Analysis Preliminary Hydrostatics Analysis List of Boat Builders Suited to the Project Designer's Cover Letter to Builders Sample Owner's 'Request for Quotes' Letter to Builders For smaller vessels there will be three drawing sheets at this point. For larger vessels there may be two or more sheets in each category. The goal of Stage II is that enough information be presented in the Estimating Plans Package that firm quotes can be obtained from prospective builders for construction of the vessel. If you would like to review an example of our design work up to this point, Estimating Plans are available for any of the designs listed on our Plans List page. Stage III - The Building Plans During ' Stage III ' the remaining design work is completed. With additional owner and builder feedback, further decisions can be made with regard to equipment and finish as needed. The drawings, Equipment List and Vessel Specification are refined and the remaining drawings are completed in order to create a final Building Plans package. These drawings and documents will finalize the interior and exterior details, the machinery arrangement, the deck plan, scantlings, construction sections, the boat's final dimensions and hull shape, and the as-designed displacement, range, performance, hydrostatics and stability. The Building Plan Drawings will include: Outboard Profile: Sail plan or other exterior details of the hull Deck Plan: Cabins, hatches, fittings, mooring and anchor gear Interior Profile and Arrangement: The vessel's accommodations Sectional Views: Structure and interior joinery sections Inboard Profile: Structure and primary equipment Various Structural Details as needed Mechanical / Machinery Details as needed Rudder Details Spar and Rigging Plan as needed Hull Fitting Details Hatch and Deck Fitting Details Companionway, Door and Portlight Details Interior Joinery Details Lofting Conventions Drawing Lines Drawing Several of the above drawing categories may include a number of individual sheets. Depending on vessel size and complexity, the Building Plans may include anywhere from 10 to 40 or more drawing sheets. During Stage III the Equipment List and Vessel Specification are finalized in order to accurately describe the intent, the layout, the scantlings, the construction, the systems and the outfit of the vessel. In addition to the above listed drawings, the following Documents will be included in the Building Plans set: Equipment List: The complete list of equipment items. Vessel Specification: Details of the intent, rationale and construction. Painting Specification Scantling List Welding Specification for metal structure Fastening Schedule for wooden structure Laminate Schedule for GRP structure Offsets Table (unless the vessel will be NC cut). Power and Range Analysis Report Weight Budget Summary Hydrostatics Report Stability Compliance Report Cover Letter to Builder Having finished Stage III, the Design Phase of the new yacht will be complete. Sufficient information will be contained in the drawings and documents to allow any professional or amateur builder to build the vessel as intended. Then the Construction Phase of the project may begin. Standards Used Design Goals : Throughout the design process we have the following goals: Suitability to the owner's requirements and to the intended service. An interior and on-deck layout per the owner's requirements. A pleasing aesthetic. A thorough specification to assure longevity and ease of maintenance. Sensibility of structure for the sake of ease of construction. A functional and accessible machinery and equipment layout. A distribution of weights to provide correct trim and adequate stability. Performance suited to the expectations of the vessel type. Structure per classification society scantling rules. Stability per international criteria. The general attributes of seaworthiness, seakindliness, strength and durability are considered to be requirements for each of our designs. It is interesting to note that for private yachts within the US, there are no requirements for stability or for structure. However if a US yacht is to be used commercially or Classed and built under survey, one or more of the following standards will apply. Whether or not a private yacht will be Classed, it is our position that all yachts be held to the following standards. STRUCTURE : When creating a new design, classification society rules are the best guide for the adequacy of structure. We will confirm compliance with one of the following rules as appropriate to the vessel type, size, materials or build venue (for more information, see our article on Designing to the ABS Rule ): ABS 2000 Motor Pleasure Yachts (applicable to motor yachts from 79' to 200' scantling length - all materials - now obsolete for yachts) ABS 1994 Offshore Racing Yachts (applicable to sailing yachts from 79' to 100' scantling length - all materials - now obsolete for yachts) ABS 2016 Steel Vessels (applicable to steel vessels up to 295' scantling length - obsolete for yachts, but still required by the CFR for commercial yachts carrying passengers) ABS 2016 Yacht Rule ( new rule applicable to all motor and sailing yachts in all materials up to 90 meters scantling length (295 feet) ISO-12215 for vessels subject to the EU-RCD standards (yachts up to 78' measurement length - all materials) Germanischer Lloyds (wooden yachts up to 78' scantling length - under revision as GL and DNV begin to merge their rules) Germanischer Lloyds (plank-on-frame commercial wooden vessels up to 115' scantling length - applicable to larger vessels on approval) British Lloyd's Register (plank-on-frame wooden yachts up to 98' scantling length - applicable to larger yachts on approval) STABILITY : To assess stability we use a variety of criteria depending on vessel size, use and location, as follows: For private yachts under 24 meters measurement length (78 feet) intended for registry in the EU, stability will be calculated according to the EU-RCD standards (ISO-12217). For private or commercial yachts above 24 meters measurement length, stability will be calculated according to IMO, MCA or other standards appropriate to the vessel type, size and use. For commercial charter yachts in the US, safety and stability will be calculated according to the US Code of Federal Regulations (CFR). For private or commercial yachts in the US, stability will be calculated according to the new ABS 2015 Rules for Building and Classing Yachts, which defer to the IMO or MCA standards depending on vessel type and size. For yachts in Canada, stability will be calculated according to criteria established by Transport Canada, which for the most part defer to to the IMO or MCA rules. For yachts in other locations, stability will be calculated according to locally applicable criteria - most often the IMO or MCA rules, depending on vessel type, service, and size. When a vessel is destined for construction and use within the European Union, we also prepare documentation regarding structure and stability in order to make obtaining a CE Mark a relatively easy process for the builder. Construction Support Services We ordinarily recommend that plans be submitted to a few selected yards for their construction estimates. We have worked with a variety of builders in a number of places worldwide. We will try to match a project with an appropriate builder, even if that may be outside the US. During the Construction Phase of the process, there may be various requests for additional services in support of construction. Although we don't get into project management per se, we remain available to act as the owner's representative during construction whenever we are asked to do so. In other words, although we do not get involved in managing personnel, scheduling or purchasing, we are pleased to remain involved in order to manage the flow of information and specifications for the builder. Additional Drawings, Documents, Schematics... Ordinarily, system schematics are developed in-house by the builder (e.g. plumbing, fuel system, etc.) or by system suppliers (e.g. electrical, hydraulic, air conditioning, etc.). On occasion the owner or builder may request that we provide basic schematics or additional drawings to illustrate specialized features or other details in support of construction in order to communicate specific owner requests to the builder. For passenger vessels or other commercial craft there may be the requirement to provide additional drawings and reports for documentation and compliance with the relevant standards. And when a vessel is destined for use within the European Union, we can prepare documentation that makes obtaining a CE Mark relatively easy for the builder. NC Cutting Files One of the most valuable Construction Support Services we provide for metal boats is to develop NC Cutting Files in order to automate a portion of the vessel's construction. What is NC...? It simply means Numerically Controlled... By this method a numerically driven plasma or water-jet cutter can be used to create frames and plates for a metal vessel. One can also use an NC driven router to cut mould frames for a wood or composite superstructure. It is even possible to carve an entire male plug or female mold out of foam for use in building a composite superstructure, directly from the computer generated surface model that was created during the design of the boat. This leverages the work that has already been done in order to create the design and can provide a significant labor savings to the yard. It also dramatically improves accuracy of construction. With NC cutting, the labor saved during fabrication of a metal hull will usually pay for the cost of developing the NC cutting files, plus some. In other words NC cutting is an opportunity to not only effect a true cost savings by shortening the overall build time, but to also improve the quality of the result. The Role of the Computer Designing the Boat : We use the Maxsurf family of software products, a series of programs for hull modeling, analysis, and construction. With Maxsurf, a preliminary hull model is quickly generated and an initial round of hydrostatics, stability, and performance calculations performed to see where the design can be improved. The computer generated model allows the design to be enhanced quickly at an early stage of design before it has become fixed, or even to be modified without too much fuss later in the process. In fact, without such an easily used computer modeling tool (as compared to manual drafting) those subtle refinements would rarely be undertaken even if given a substantial budget. Several other benefits are also evident. For example, via the computer generated model it is easy to assure that the surfaces are developable, so building a metal or plywood hull is made simpler. Testing the Design : With the computer generated model of the hull and superstructure having already been created, it is a simple matter to make a scaled down physical model for towing tank testing, or to verify the styling and features of the yacht in three dimensions. Building the Boat : A substantial benefit of having generated a model of the hull on the computer is that the vessel's structure can also be computer generated and actually pre-cut via computer guided laser or plasma cutting - or in the case of a GRP vessel, the mould created using a computer guided router. By this method, having detailed the hull plating and structure, the parts are nested onto available plate sizes. The completed plate nestings are then sent to the metal cutters - usually by email. This is extremely convenient since the cutter can receive the information immediately in order to start the work. When completed, the cutters have a "boat kit" that can be shipped wherever needed. The Savings : When building a metal boat in a production environment, assuming one-off construction, industry feedback is generally that NC cutting will save a professional builder some 35% or so of the hull fabrication labor. The percentage of fabrication labor saved by an amateur owner-builder is dramatically greater. For example, consider that lofting is eliminated, as are templating for frame and plate patterns. For an amateur builder, this also eliminates most of the "what to do and how to do it and why" kind of worries... Other Benefits: Via NC cutting an extremely accurate fit results. For a metal hull this means there will be far less distortion during the weld-up. For construction in other materials such as GRP, NC cutting nearly eliminates the labor required for lofting and for mold construction. An entire hull and superstructure mold can be carved by five axis NC router directly from the computer generated model, avoiding nearly all tooling labor. A builder can also pre-cut glass fiber or carbon fiber cloth, especially useful with 'pre-preg' cloth (cloth that is pre-impregnated with resin and post-cured by UV or by heat). Where the materials cost is high, the improved efficiency will quickly offset the cost of having developed the structure via computer modeling. Design-Stream Overview For more detail on our design and build strategy please see our CAD Design Stream article. The following flow-charts were created in order to show our design process - more or less taking the usual "design spiral" and stretching it out into a linear diagram. I have used two different ways to represent the work-flow. Software in Use - This is a simplified flow chart showing the software we use, and how a few basic software groups interrelate during the process of creating a new yacht design. Process & Deliverables - This is a workflow chart showing our Design Process arranged in terms of the "order of operations" that we follow in order to create each new yacht design. This process starts with our interaction with the client as described above, then moves into the stages of the design process wherein we produce the drawings and documents that we deliver to the client, the builder, and to the metal cutter. Cool 3D Models The following are two examples of how we make good use of a 3D CAD workflow in order to create a design and its structure, then to communicate the result using 3D PDF files for use by both client and builder. 3D Lines Drawing - This is a 3D perspective file showing the lines of one of our designs. As with all of our designs, it was created in Maxsurf , then imported to Microstation so that it could be "plotted" to a 3D PDF for customer review. Within the PDF, you can grab the 3D model, rotate it, zoom, pan, walk-through, and you can change the perspective. If you turn on the PDF menus, you can also manage the layers in the original CAD drawing, turning any of them on or off to simplify the view. This is an excellent tool for visualization of the spaces, and to see the vessel's shape from any angle. 3D Structure Drawing - This is a 3D perspective file showing the structure of a metal yacht design. Having been designed in Maxsurf , the vessel's structure was then created in Workshop ; after which the basic structure was brought into Microstation for editing and detailing, and then "plotted" to a 3D PDF for the builder to use as a guide during assembly. It is an excellent way to view the structure using simple, free Adobe Reader software. This enables the builder and his crew to see exactly how the structure interrelates. Why Develop A New Design...? As you may have surmised from the above, there is a fair bit of work involved in designing a boat well, even if it is a simple one! Given the number of designs that already exist it may seem a little bit wild to commission a new yacht design. On the other hand, it is an unquestionable delight to see one's ideas turned into one's own personal yacht. You will be surprised to discover that the cost to develop a new and unique yacht design is ordinarily less than a yacht broker's typical fee to purchase an existing yacht...! I'll repeat that in case you missed it... Even though there is quite a lot more work involved to create a boat design, the cost to create a new custom yacht design is ordinarily less than a yacht broker's fee for the simple act of signing the purchase papers...! As a percentage of the yacht's cost the amount expended on design is really not very much. If you also consider that a custom design will be tailored to your particular requirements rather than being an "off-the-shelf" solution, the difference in satisfaction will be well worth the effort expended. This is especially so if a custom designed yacht will better serve its intended purpose and will therefore be able to do so for a longer time, versus a vessel built to a stock design. In other words, by not having to replace the yacht quite so soon, the cost of custom design work will easily have paid for itself, in all likelihood many times over. Is It Proven? The question inevitably comes up: " Is it a proven design?" The answer is an unqualified " Yes !" The basic principles of boat design, while seemingly complex, are well established. If faithfully attended to, the success of a new vessel is assured, and the result will nearly always be an improvement on what has been done before on existing designs. Where unusual features or hull types are requested, it is prudent to involve tank testing, which can provide valuable insight as to vessel behavior; performance; stability; seakeeping; etc. What ultimately makes a boat a success is whether the vessel is safe, seaworthy, sea kindly, beautiful to behold, and above all, whether the vessel satisfies the originally stated wishes of the owner. Establishing a Design Philosophy... My aim is to engender superior aesthetics along with safe and comfortable boating. A distinguishing characteristic of our design work during the last few decades has been a focus on Nomadic Watercraft , in other words the design of truly pelagic blue water boats for family cruising and world voyaging. I strive for long term owner satisfaction with the resulting vessel, using the most up to date methods and design tools, including software optimized for hull modeling, stability and performance analyses. With this approach, I am able to leverage the work done to create the design into subsequent detailing of the vessel's structure in order to provide an NC cutting file package to automate parts of the vessel's construction, a process that is outlined in our CAD Design Stream article. My goal is to provide a complete "design service" from the point of imagining the vessel, to creating the ideal solution to those conjurings, in other words to take the concept all the way from 'napkin sketch' to building plans, and to then provide the various "construction support services" noted above. Where To Begin? The place to start the design process is to first create an Owner's Specification, or "mission statement." It need not be more than a few paragraphs that describe the proposed vessel, or possibly a simple list of desired features such as overall size, operational requirements, preferences with regard to rig, power, equipment, materials of construction, accommodations, budget, project timing, and so forth. The 'mission statement' need not be elaborate, since the vessel's particulars will be generated during the design process itself... however where specific requirements exist, they should be articulated. While sketches or design examples are not necessary, if preliminary sketches or design examples are available and relevant, they should be included. Once I've understood your requirements I will provide a written ' Design Proposal ' - usually by return email. Our Design Proposal is offered at no cost, and implies no obligation; it is just good information for your planning purposes... As for the inevitable questions regarding the cost of boat custom design, our Design Proposal will answer them definitively, however please also see our Articles On Costs involved with boat design and boat building. In order to pursue a design inquiry in greater detail, please feel free to contact me for more information or to request a Design Proposal . Creating a new yacht design is by far the most rewarding path to long term boat ownership, and the process itself can be quite a lot of fun...! What do our clients think...? Please review some of their Testimonials to find out... Member Royal Institution of Naval Architects Member Society of Naval Architects and Marine Engineers Member Society of Boat and Yacht Designers Member American Boat and Yacht Council Member Metal Boat Society

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Yachting World

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America’s Cup boats: How they work and why they’re unique

Toby Heppell
February 5, 2021

The America's Cup boats to be used on the 2021 edition of the event are unlike anything we have seen before. They might be officially sailing craft but they behave in some remarkable ways.

The AC75s, the America’s Cup boats currently racing in the Prada Cup and that will be used for next month’s Cup match showdown, are arguably the most radical boat the America’s Cup has ever seen.

The America’s Cup is, fundamentally, a design competition, and successive America’s Cups have featured the most extreme yachts yet – for their time – ever since the first race in 1851 .

However, the foiling boats we have seen in the last three editions of America’s Cup racing (the AC72 and AC50 catamarans, and now the AC75 monohulls ) do represent a new direction for the highest level of sailing.

There are plenty who argue that this technology is so far beyond the bounds of what most people consider sailing as to be an entirely different sport. Equally, there are those who believe this is simply a continuation of the development that the America’s Cup has always pushed to the fore, from Bermudan rigs, to composite materials, winged keels, and everything in between.

Good arguments can be made either way and foiling in the world’s oldest sporting trophy will always be a subjective and controversial topic. But one thing is certain: the current America’s Cup boats, the AC75s, are unlike anything seen before and are showcasing to the world just what is possible under sail power alone.

American Magic hit an impressive 53.3 knots on their final weekend of racing. Photo: COR 36/Studio Borlenghi

1 Unimaginable speed

In their final race before being knocked out of the competition , American Magic’s Patriot registered a top speed of 53.3 knots during a bear away.

Topping the 50-knot barrier used to be the preserve of extreme speed record craft and kiteboarders. A World Speed Sailing Record was set in 2009 of 51.36 knots by Alain Thebault in his early foiling trimaran, Hydroptere , and was bested in 2010 by kite boarder, Alexandre Caizergues who managed 54.10 knots.

O nly one craft has ever topped 60-knots, the asymmetric Vestas Sail Rocket , which was designed for straight line speed only and could no more get around an America’s Cup course than cross an ocean. Such records are set by sailing an average speed over the course of 500m, usually over a perfectly straight, flat course in optimum conditions.

America’s Cup class yachts, designed to sail windward/leeward courses around marks, are now hitting speeds that just over a decade ago were the preserve of specialist record attempts, while mid-race.

Perhaps even more impressive, in the right conditions when racing we have seen some boats managing 40 knots of boatspeed upwind in around 17 knots of wind. That is simply unheard of in performance terms and almost unimaginable just three or so years ago.

Photo: COR 36/Studio Borlenghi

2 A storm onboard America’s Cup boats

Related to the speeds the boats are sailing through the water, particularly upwind, is the wind speeds the sailors will feel on deck.

When sailing, the forward motion affects the wind we experience onboard, known as apparent wind. The oft’ trotted out explanation of how apparent wind works is to imagine driving your car at 50mph. Roll down the window and stick your hand out of it and there will be 50mph of wind hitting your hand from the direction your car is travelling.

Article continues below…

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So when an AC75 is sailing upwind in 18 knots of breeze at a boatspeed of 40 knots, the crew on deck will be experiencing 40 knots of wind over the decks plus a percentage of the true wind speed – depending on their angle to the wind.

The AC75 crews might be sailing in only 18 knots of breeze – what would feel like a decent summer breeze on any other boat – but they experience winds of around 50 knots.

To put that into context, that is a storm force 10 on the Beaufort scale!

Once up on the foil, everything to windward of the leeward foil generates righting moment. Photo: COR 36/Studio Borlenghi

3 Righting moment changes

The single most radical development of the AC75 is to take a 75ft ‘keelboat’, but put no keel on it whatsoever.

When the America’s Cup Defender and the Challenger of Record, Emirates Team New Zealand and Luna Rossa Prada Pirelli respectively, announced the 36th America’s Cup would be sailed in 75ft monohulls, conventional wisdom had it that the boats would look something like a TP52 or a Maxi72 – both impressively high performance keelboats.

By doing away with the keel entirely, the design is now like nothing we have ever seen, particularly when it comes to how dynamic the power transition is between foiling and not foiling.

The boats are designed to foil on the leeward foil, with the windward one raised to help increase righting moment: to help balance the boat. This means that when the AC75 is not foiling they are extremely tippy – much more so than most other boats of the same size.

Essentially, when the wind catches the sails, the boat wants to fall over as there is too much sail area for the amount of weight underneath the boat – something a lead keel usually counters on a yacht or keelboat.

Once the boat is up and on the foils, however, that all changes, as everything to windward of the single foil in the water balances the sails. That means, the hull, the crew weight, the sail and rig weight, and the windward foil, all work to counter the sails.

What all this means is that the boats go from being extremely tippy, to hugely powerful in just the few seconds it takes to get up on the foil. “The [AC75s] are really very tippy pre-foiling and then they go through the transition where they will need to build significant power. Then immediately [once they lift off] you have more stability than, well, take your pick, but certainly more righting moment than something like a Volvo 70 with a big canting keel.

“That change all happens in a very short space of time,” explained Burns Fallow of North Sails, who was one of the team who developed the soft wing concept back when the concept was revealed.

With lift created to windward by the foils, it is possible that the boats can sail diagonally to windward. Photo: COR 36/Studio Borlenghi

4 America’s Cup boats may not be heading where they point

With the AC75 sailing on its foil, drag is dramatically reduced, vast amounts of power can be generated and so speeds rapidly increase. But the foils can serve another purpose too.

In order to be able to lift each foil out of the water, the foil arms must be able to be raised and lowered. Hence the foil wings, which sit at the bottom of the foil arms (and are usually a T or Y shape), do not always sit perpendicular to the water surface and the AC75s often sail with them canted over to something nearer 45º to the surface.

The further out the leeward foil arm is canted – essentially more raised – the closer the AC75 flies to surface and, crucially, the more righting moment is generated as the hull and rest of the boat gets further from the lifting surface of the foil.

There is another positive to this: as the lifting foil is angled, it produces lift to windward, which can force the boat more towards the wind than the angle it is sailing.

Due to this negative leeway (as it is known when a foil creates lift to windward) the boat can be pointing at a compass heading of say 180º but in fact will be sailing at eg 177º as the foil pushes the boat sideways and to weather, essentially sailing to windward somewhat diagonally.

5 The foils are heavy. Very heavy.

As the foils work to provide stability to the boat (when it is stationary both foils are dropped all the way down to stop it tipping over) and to provide massive amounts of righting moment, they are incredibly heavy.

A pair of foil wings and flaps (excluding the one-design foil arm which attaches them to the boat and lifts them up and down) weigh 1842kg. To put that into perspective, the entire boat itself with all equipment (but without the crew) weighs between 6508kg and 6538kg. So the foil wings at the base of the foil arms are nearly ⅓ of the total weight of the boat.

It is partly due to this that you will see some teams with bulbs on their foils. If you decide to go for a skinny foil wing (which would be low drag and so faster) then there will not be enough volume to cram sufficient material in to make the foil weigh enough. So some teams have decided to add a bulb in order to make it weigh enough but to also keep a less draggy, slimmer foil shape.

6 Sails can invert at the head

As with everything on the AC75, the mainsail is a relatively new concept. It consists of two mainsails which are attached to both corners of a D-shaped mast tube. This has the effect of creating a profile similar to a wing.

It is well established that solid wing sails are more efficient at generating power than a soft sail and for this reason solid wings were used in both the America’s Cup in 2013 and 2017. But there are drawbacks with a wing: they cannot be lowered if something goes wrong and require a significant amount of manpower and a crane to put it on or take it off a boat.

One reason a wing makes for such a powerful sail is that the shape can be manipulated from top to bottom fairly easily with the right controls. With the AC75 the designers wanted a sail that could have some of this manipulation, produce similar power but could also be dropped while out on the water. The twin skin, ‘soft wing’ is what they came up with for this class of America’s Cup boat.

In addition to the usual sail controls, within the rules, the teams are allowed to develop systems for controlling the top 2m of the mainsail and the bottom 1.5m.

What this means is that the teams are able to manipulate their mainsail in a number of different ways to develop power and control where that power is produced in the sail. But it also means that they have the ability to invert the head of the sail.

Doing this effectively means ‘tacking’ the top of the sail while the rest of the sail is in its usual shape. The advantage here is that instead of trying to tip the boat to leeward, the very top of the sail will be trying to push the boat upright and so creating even more righting moment. The disadvantage is that it would come at the cost of increased aerodynamic drag.

We know that a number of America’s Cup teams are able to do this, though whether it is effective is another question and it is very hard to spot this technique being used while the boats are racing at lightning speeds.

Photo: Emirates Team New Zealand

7 An America’s Cup boat generates lots of data

A new America’s Cup boat is a vastly complex bit of kit. Each team has incredibly powerful Computational Fluid Dynamics (CFD) software packages and simulators in order to try to understand the various gains and losses.

To make these simulators and computer projections as accurate as possible each team has been getting as much data as they can over their three year development cycle.

In the case of this America’s Cup it does seem the development process is genuinely getting closer to Formula 1 (albeit with smaller budgets than a modern F1 team has behind them).

INEOS Team UK have been able to work alongside the all powerful Mercedes F1 team (both of who are backed by INEOS) and have been open about how much this has helped their development process. They even have some Mercedes staff out with the team in Auckland assessing their data.

“It’s really similar to F1,” explains Mercedes Applied Science Principal Engineer Thomas Batch who has 11 F1 titles to his name and is with INEOS in Auckland. “Certainly in this campaign the technology is close to what we have in F1.

“In terms of raw sensors on the boat you are probably talking in the 100s but then we take that and we make that into mass channels and additional analysis with computational versions of those channels that we then analyse and get into in more detail. So you are looking at 1000s of plots that we can delve into [per race or training session].

“That level of data analysis and then feedback with the sailors is very similar to working with an [F1] driver.”

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Home » Rules of thumb for boat and yacht design – are they legitimate?

Rules of thumb for boat and yacht design – are they legitimate?

A creak of leather as he climbs on his hobby horse.

I sortof have a mission against using rules of thumb for boat, and particularly sailing boat design.

The problem is that often they have been stripped of the original context. A particular type of boat or a particular situation.

I haven’t really seen any that hold up in all situations – or at least very few.

Example 1 – Sail Area to Keel area

One rule of thumb that crawls around the net is that the centreboard area should be a particular proportion of the sail area. It is set up to work for yachts, but by the time you get down to small boats they travel so much slower that you need a lot of extra area.

My take is that for dinghies and other light boats (take that as missing context in the original) the centreboard or leeboard should be getting up toward 3ft deep and 10 inches wide.

If a boat carries a trapeze or leaning plank or is flared widely the area and probably depth will need to be tweaked up more the close you get to 16ft.

Inevitably if I write this often enough it will become a rule of thumb itself!

The risk is that the numbers will be presented as an absolute size as the contextualising information is gradually stripped away.

The original “rule of thumb” is even wrong for yachts. We know now that the depth of the centreboard, leeboard or keel is much more important than the area.

Example 2 – that you can stretch or shrink an existing boat by X%

One “rule of thumb” for boat design that continually comes up – and I got bitten by it once.

A customer asked for advice and someone gave him the impression it was OK.

This resulted in a boat that wouldn’t sail at all because it was too unstable and a customer unhappy with me.

A builder contacts me and says “something wrong with the boat” he built to my plan. Later I found that the 15.5ft Goat Island Skiff had been shrunk to 14ft. Article here .

That “rule of thumb” that is quoted is that you can generally shrink or expand a boat 10 or 15% with little problem. But this one is so wrong that it is a real danger.

15% reduction in overall dims and stability is halved.

The source often quoted for this is Bolger – who once said that a cargo boat could be increased in length by adding a 10 or 15% section in the middle. And with a possible improvement in fuel consumption.

Completely different statement. Not only is the body of a cargo boat mostly parallel sided in the middle, making the mod easier, but Bolger was tempering it with his vast experience.

He mentioned it only as a “notion” and certainly didn’t just add a bit in the middle. But drew it out carefully and properly as a new design.

Example 3 – the mast on the small boat should be three times the beam

Now for the Chappelle comment that mast length being 3 times the beam. Clearly he is talking about stability. So when he is talking about a specific model and size of boat he might be right … but what rig is he talking about – does he mean the peak/head of the sail? A lug sail could almost have double the area of a triangular sail under this “rule of thumb”.

These three boats have about the same mast length. The lug is 105 sq ft and the triangular sails are 82 sq ft.

But there is a more serious part to the argument.

In general if you double the size of the boat the stability goes up by a factor of 16. But the heeling forces go up by a factor of 8.

This is why a maxi yacht can either have a lighter keel – or like the modern ones be somewhat narrower than a smaller boat of roughly the same proportions – note the really long keels on model boats.

This pic shows a keel depth about half the length of the hull. The full size boat would need a keel 35ft (10m) deep – not necessary though

The best guide is looking at existing boats built to a similar purpose. Then identify which ones are good sailors and keeping to the same rough proportions.

Beyond that you can make sensible conclusions. Like an Oz Goose is more stable than a pointy nosed boat and put a bigger mast and sail in it. That is assuming it has a similar position of the centre of gravity.

Or that a new design will sail a little faster so maybe the centreboard can be made a little narrower.

Howard Chapelle knew exactly what he meant by the comment. But it has been pulled out of context by being turned into a “rule of thumb”.

Legitimate rules of thumb?

There are a couple of areas where I use rules of thumb.

Francis Herreshoff once said that the rake (angle back) of each mast on a boat needs to be 2 degrees more than the mast further forward. This is to simply prevent the masts look like their tips are converging. It is simple, it works and is not very open to interpretation. It also doesn’t have any effects beyond its brief.

Another place I use rules of thumb is in construction. For plywoods under 9mm an epoxy fillet needs to have a radius three times the plywood thickness. Same if you use a piece of timber in the join – the glue cleat needs to be have three times the gluing area to the ply of three times the ply thickness.

This is another rule that falls apart if taken too far. Testing shows that the fillet radius actually needs to be about 2.2 times the ply thickness. So there is a safety factor already applied (someone is always ready to “add a bit” for safety. Not necessary

But as the ply thickness increases the rule falls apart as you need to add glass cloth to get enough strength. And by that stage if you rely on fillets only then the fillet has so much volume that it has become crazy expensive.

So, I would suggest that rules of thumb are very useful for professional designers because they know the ramifications. It is easy for Bolger or Chapelle to know what they mean. AND know when the “rule” breaks down. But a better guide for amateur designers is to look closely at similar sized boats to see which ones perform well in terms of meeting the required use patterns. And which ones do not.

Cautions on copying current practice – beware of creep

A problem with looking at current practice as a standard is that it can go badly wrong if you just look in one place for information.

One example is plywood canoes and kayaks.

When I got into wooden boat building in the late 1980s it was common for a stitch and glue kayak to be built of 4mm (3/16″) ply and glass taped with 50mm (2″) tape inside and outside the seams.

This was also common for plywood racing dinghies in Australia and New Zealand. Which are subject to very much greater loads. This one is composite, but the sail area has slightly reduced over the years.

By 2000 the standard way was to use glass tape on the inside of the boat but outside of the boat in 4 or 6 oz (125 or 200gsm) glass cloth.

By 2010 several major manufacturers of kits are saying you have to build the boat with the boat completely sheathed with glass inside and out. As any builder knows – glassing the inside of a built hull is a cow of a job.

But it adds significantly to the expense, the cost and weight of the structure. Some say that glass has negligible weight – they obviously haven’t had to lug a boat very far!

Others say it is to get an “I-beam” or “composite sandwich” effect. This is misunderstanding how materials work. ALL materials loaded in bending, whether by having weight in the middle, or by water pressure work by the same method. It just has to be strong enough for purpose.

If you are expeditioning and doing rock shore landings it might be worth going to glass inside and outside. But this is not what 99% of users do.

An example of why most Kayak plans are overbuilt and overcomplicated …

One last parting shot … this is a Jarcat – a very clever range of trailer catamarans designed by Ross Turner in OZ. There are hundreds launched.

The Jarcats in the 16ft range is built of the same 4mm ply – with 20z glass on the outside only. A case of “creep”. A small step by step change which is not perceptible – but ends up a long way from the original point with little real justification.

Either the kayak designers or the Jarcat is right – the other wrong. With 500 or more Jarcats on the water …

I only found this out in the last couple of years.

Despite the Jarcat being around for a couple of dozen. My bad.

It has made me think that for most boats in dinghy size that are going to be glassed that some glass is more important than the actual weight per metre of the glass. Also think WHERE the glass is really needed.

Alternatively the earlier practice from the 60s and 70s might indicate that glass taping is all that is really needed. For most boats and most normal uses.

So it is sensible for amateur – and all designers – to look broadly and find out what is the actual best practice across a wide range of boats rather than accept things that are touted on the internet. Do your own research and share your conclusions.

Like this article! :-)

An article by the technical wizard Eric Sponberg regarding rules of thumb for boat design.

29 thoughts on “rules of thumb for boat and yacht design – are they legitimate”.

I agree and disagree with the rules of thumb position the author states. How committed to the rule are you in finanacial terms, and can you adjust and tune from there? is it an emergency? If you built a boat by rules of thumb and could tune it after the first few runs, you could get a real good boat, that fits your style. If you get dismasted how much sail do you need? broke the rudder? how big was it? how close to the rule of thumb does the deck plate swept oar you made in an emergency come to the rule? My drag racer back ground is all rules of thumbs then tune tune tune. If you jurry rigged a lee board by the rules of thumb then tuned it in practise before you made permanent mounts you would hace s good chance to build a hell of a boat.

Good points … you do need somewhere to start from. Whether it is to look at a boat (or drag racer) that is similar or search for some formula, equation or methodology.

Sometimes rules of thumb can work. And that’s why context is important.

The difficulty is that the “rules of thumb” are often used as a one shot method as a package solution.

But if there is a tuner/tinkerer’s culture like drag racing it can be a very successful method.

However, most boats are built just to use and not to worry about.

And I’m sure in the drag racing world there are lots of people who have read a bit … and then those who actually have been committed for a long time and actually gone up the practical learning curve of actually competing and seeing how the ideas pan out.

The first group are not so useful. But the guys up the real learning curve who have tested the rules of thumb and found them worthy .. or unworthy .. their words are like gold.

The only rule of thumb I cling to religiously is that when someone starts flinging around ‘rules of thumb’ too casually, he gets beaten with a stick no bigger than my thumb.

Seriously, though, this is a great discussion! As a designer of things wooden, I find some of my most exciting failures and successes come from challenging my own developed-over-time patterns and assumptions. “Hmmmmm…. it’s probably crazy, but I wonder what would happen if I ignored reason and…”

Too much modern stuff — should be a discussion on “rule of digital calculator”….

The penny (size) of a nail used to fasten a plank on a wooden boat is one penny for every eight of an inch of thickness of the plank. For softwoods, add two pennies.

The general rule for lower mast diameter was 7/8 inch for every foot of beam.

Beveling for caulking: the outer edge should be beveled 1/16 for every inch of plank thickness; beveling from the center of the plank.

https://web.archive.org/web/20151025144750/http://www.tsca.net:80/CRBB/thumb.htm

Thanks for the comment.

I can only agree. Like PAR says above, that going straight in and grabbing the pocket calculator and thinking it is going to work is a mistake.

I use computers for my design work, but really, it is only for the laying out of the lines and doing the calculations. You still need to know what the results of the calculations mean! :)

Similar with rules of thumb. The middle one is probably correct for a certain type of boat the builder was used to building, but will fall apart for different types of boats. For example a light dinghy 5 ft wide and 13 ft long compared to a classic square metre style yacht which might be about 30ft or longer on the same beam. But kept within its original intention of size and type it probably performs admirably.

I rather tend to trust constructional rules like your other two, but usually do check them against the result from more modern standards. Maybe not all that modern if we are talking about rivets – maybe I mean I will check a couple of other sources just to make sure I’m not overdoing or underdoing it.

The first couple of boats I designed were laid out full size on the floor. Because that’s the way I had been building them until that point. As I got used to computer design tools I understood very clearly that it really is the same process as drawing on the floor, except the calculation results are available more quickly and more accurately.

The computer model has to come back to wood at some point – so if you try to make the lines on the computer do something that wood won’t do when the boat is actually built, it will turn around and bite you quite badly.

This is probably a good thing.

For what it’s worth Mik, I keep my rules of thumb to myself, if for no other reason, then to prevent it from becoming a generally accepted rule of thumb. In reality, I keep it because I can use this information to advantage.

For the most part we’re in agreement in that these rules of thumb are worthless, for the novice sailor or budding designer and can cause much more harm then good, if considered more then what they are, which is a very rough and general guide, typically for comparative uses.

I have a secret rule of thumb for finding a wife, but it’s use hasn’t worked well for others, for their lack of understanding of it’s implementation.

Most of us in the industry, use rules of thumb without thinking about them. By this I simply mean we’ve developed such a sense of proportion and understanding about the way things work, that we can guesstimate fairly closely what a prospective boat’s displacement might need to be, to meet the SOR, general hull form shapes, approximate sail area necessary for the preformance envelope envisioned, etc., etc., etc. This is using the rules of thumb, possably on a subconscious level to a degree, as I for one don’t think about it, I just know or have a feel for what’s right, before I run the math. It’s rare for me to be surprised by the “numbers”

Another example would be a fast daysailor I did not too long ago. She was a narrow V bottom boat, with a fairly flat chine, so she’d be good up wind, if you can hold her down and have less leeward bow wave resistance, then a hull with a dramatic chine sweep at the bow. This naturally meant the sail area would be somewhat less then the ideals for a fast dayboat. So a moderate WS/SA and SA/D are the result. Just looking at these to figures you’d think she wasn’t particularly impressive, but having sailed the prototype at over 16 knots, this isn’t the case. She does all the things I expected, including pound hard going to windward, because of the flat chine choice (see, I didn’t say compromise, even though you know it was).

Most of the “rules” are as Mik suggests and just a general guide to compare against other, similarly sized craft. Once you generate some experience and more importantly success with design, you harbor favorites, a keenness for certain things and an understanding of the “relationships” with the “numbers”. These become second nature after a while, as you build on successes and learn from not so successful attempts. This understanding then becomes a set of personal rules of thumb. You may wish to test or stretch the rules from time to time, but most of the designs you work on, will usually fall right inside the comfort zone your personal rules create.

Completely agree Paul,

The first para in my article talks about the “context” of the rule of thumb. We all have shortcuts as designers.

The risk is when the “rule of thumb” loses its original context.

As designers we have some experience to back up our use of rules of thumb. Often because we have the chance to make mistakes – usually of the smaller kind – like the centreboard on my original BETH sailing canoe being too small. Handling could only be describes as lazy and performance disappointing upwind. I made another board with 9″ more depth and she became pretty good upwind – not quite good enough to stay with a well sailed Laser, but not embarrassingly far off the pace either.

Or sometimes further experience can show us that the rule of thumb is just wrong. Like the excessive glass recommended for kayaks one or the “you can shrink or expand a boat 10 or 15% with few problems” one.

Though it is hard to know if these are wrong because of a change of context or loss of context.

But I would generally think, that if a simply stated rule of thumb appears to be applied universally then it is highly suspect.

Also a good rule of thumb is if something is made heavier and stronger over the years … then it is very probably being overbuilt or overdesigned.

In other words there needs to be a realistic justification for it, rather than some sort of nebulous “creep”

Thanks again!

Hi Mik, I use rules of thumb all the time, but generally I don’t think they are understood by the budding or would be designer.

A good example of this is a custom design I recently started. It’s not a modern boat, but a “in the spirit of” type of design and a cruiser of about 26′ (7.9 m). In this vain I knew I wanted an SA/D in the 16 to 18 range, but since he would likely spend time in the trades occasionally, I elected to be on the low end of this rule of thumb for a cruiser. She carries a 15.7 SA/D, but has light air hoist options to jack this up to 25 if desired.

For comfort I elected to go after a moderate D/L, but also to help preformance I stayed on the low side of the rule of thumb and she ended up as a 266 D/L.

The amount of sail area rule of thumb, based on wetted surface supplies well and under working sails she’s a 2.2, again in keeping with her cruiser status, though under light air sails, this is a much more respectable 2.6, so she’ll fair very well in soft wind strengths.

As far as the 3 times the beam thing, well this is as absurd as you make it in your piece, but maybe it once had some value. We are also in complete agreement when it comes to scaling up or down a particular design. In fact, this is a very common request for a designer. “Hey, can I have this boat, just 20% longer?” My reply is much like yours and a quickly uttered “nope”.

As far as keel area, well I didn’t have a problem here as she’s a full keeled boat, though the forefoot is well cut back, partly to optimize the appendage for the rig choices, but mostly to get her to maneuver smartly. Her skeg hung rudder, does fall within the usual rule of thumb for selecting it’s area, but I didn’t use it as a guide. I had only so much room left under her after the sail drive leg, so I filled most of what’s left with the skeg and rudder assembly, of course with sufficient enough separation to make the skeg useful.

I guess my point is, rules of thumb can be very handy, particularly in the conceptual stages of the design spiral. The important thing is knowing how and when to employ them. For the most part they are useless in all but the beginning of the design stages, more a ball park type of thing.

Telling someone they should shoot for a 2.45 wetted surface to sail area ratio is meaningless, unless you know what this will bring to the other perimeters and particulars of the design. For example (again) this WS/SA ratio would be too “tall” on a narrow, slack bilged craft or grossly under canvased on a canoe body with fat hind quarters. You have to know where, how and when the apply and most importantly their limitations and/or implications to the rest of the project.

Rules of thumb don’t govern the design, but do establish general set of target ranges to shoot at while working up the design ladder.

Howdy Paul,

Nice comments!

I think there is a difference between analysis and “rules of thumb”. But maybe I am clutching at straws?!

The ratios of displacement to length or Sail Area to Displacement are a progressive estimate to break boats into different classes of behaviour. We know what the numbers should look like for a slow and steady cruiser compared to a mad planing machine and the “cruiser racers and occasional offshore surfers fit between and have their own ranges.

Those types of analysis ARE very useful because they come from real analysis.

But simple single statements that are supposed to fit all cases are highly suspect. Like “the area of the centreboard or keel should be 4% of the sail area”.

The best resource of both good rules of thumb and “stoopid” ones is Gavin Atkin’s page on The Rules (of boat design) .

Gavin has collected a whole heap of them, but I would like to throw away quite a few as complete nonsense and almost completely misleading. Each one is a great starting point for a discussion though – or a talk about boat design. Just to pick out where each is a supportable statement and where it starts falling apart – some sooner than others!

Some would do this because they are taken out of their original context. Also Gavin has juxtaposed the contradictory ones.

But the ones that try to be a single simple solution are the most suspect.

“The beam of a flat bottomed boat should be no more than half the length; if it is to be rowed or sailed, the length should be two and a half to three times the beam – HV Sucher”

The list is huge FUN though and lead to other thoughts – which is exactly why Gavin posted them – note his quote at the top from Norman Skene – it is an obvious disclaimer to those who read between (analyse) the lines rather than trust the lines themselves (repeat without thinking)!

Thanks for posting!

What I should have added, to bring the post back to topic, is that all the stuff I can find out about small-craft design (and I’ve been lucky enough to talk to most of the top names) could be encapsulated in one rule of thumb that there is no one type (and “type” includes nationality) of craft that is much more efficient than the others – if you define “efficiency” as including aspects such as cost, ease of use, versatility, etc.

Howdy Chris,

I guess what I was getting at was that there are boats that can sail very well through all conditions – up and beyond the speeds of comparable boats.

When the 505 came out, it was one kind of revolution, the Tornado another. 50 years after their design these are still very close to the best standard in terms of all round performance – they have been overtaken, but not by that much!

Just as a comparison, the International Canoe, pre spinnaker was screamingly fast in some conditions, well able to burn off a 505 – but in other conditions it sails just like a standard sailing dinghy with 10sq metres of sail.

I guess that this also disqualifies my thesis about the moths! And sailboards – at least if you take one type of sailboard at a time.

But the wind speed for Moth effectiveness moves ever downwards. It must have a limit of course – there will always be a windspeed where a foiler moth becomes about as much fun as sailing a wet sock.

Thanks very much for the roundup of sailboard performance – especially the comments of bigger sails set up for better handling. When the first 7.5 sails started appearing with this thinking, I thought it might be the start of a single rig that would do for all conditions.

I agree completely and in heartfelt way with out about backyarders being slowly eliminated. With two or three main manufacturers of foiler Moths we won’t see the fast development and ability to drop blind lines of development that existed in the days of homebuilding Moths when 8 or 12 smart guys in Sydney would build new boats over each winter. Not to mention the ones in the UK. Or same for the early days of sailboards – you remember those somewhat lumpy styrene cored kevlar and epoxy creations of the ’70s? Lots of smart guys involved there too.

Pity that they decided to put a minimum wind limit in for international raceboard events. That’s the sort of rule that is often counterproductive to developing better boards. Or like allowing canting keeled yachts that have to run engines – it means that develoopment of more sensible alternatives is not supported.

Thanks for replying, Mike.

I suppose part of the issue is defining “efficiency”. Yes, we both agreed that boards are not as efficient (in some respects) as a foiler Moth. However, as compared to a non-foiling dinghy and when compared against dinghies of similar LOA or sail area, the boards are certainly efficient, as demonstrated by their superior all-round speed over the pre-foiling Moths which were arguably the most efficient dinghy of their day.

Board development has been stifled by rules, IMHO. Not that I’m against rules, but there’s no really open class left in boards. All the International classes are restricted to production boards and a certain minimum run is required. So backyarders of the type that produced foiler Moths and the original windsurfer are ruled out of the sport, which is bizarre IMHO.

The Formula Windsurfing boards are producing excellent performance, comparable to a foiler Moth when both are planing or foiling, but FW boards are very short and fat and basically cannot finish a race under about 8 knots of wind. I’d rate them therefore less efficient and slower all-round than a foiler Moth. Dimensionally, the FW board has 50% more sail but about 60% of the LOA and cost.

The Division II boards are basically dead (the class has gone and they are ruled out of other classes) but remain the fastest under about 8 knots and, according to some experts a few years ago, the fastest around a course from 0 to 30 knots because of their light-wind prowess (going as fast as a Canoe or pre-foil Moth in light winds with 7.4m of sail on a restricted platform is pretty damn outstanding, especially when you move away from the latter two in more breeze).

The advent of larger sails has improved the performance of Raceboards although the new boards (there are now three in production, a big improvement over earlier years) are basically no faster than Mistral Equipe IIs and other 1990s boards.

The larger sails may be easier to handle because of superior materials and design that has sacrificed lift per metre for superior handling. Of course, while that allows you to carry a bigger rig, it also means you have to lug that bigger rig through transitions and pay for the bigger sail and spars…. sometimes I think we over-rate the superior performance of modern flatter sails. Interestingly while windsurfer talk about light modern rigs, most sails are at least twice as heavy as the Windsurfer One Design mylar sail and the old-fashioned One Design sail appears to generate much more lift per metre.

The righting moment issue has been attacked in Formula and shortboards by making them wider, with Formula boards hitting the class beam limit of 1m. That allows them to carry huge rigs and fins. However, in sub-planing conditions the very high drag makes these boards extremely slow.

A skinny longboard with hiking racks could be a real mover, but since the longboards can already beat any comparable single-sail single-handed non-foiling dinghy you could say that speed is not the issue. Merely adding more RM would not get them to the pace of a foiler Moth around a WW/LW course,as far as I can tell. A foiling longboard would be an interesting beast!

The yardsticks are at the bottom of the on-line VYC listing but they have the Div 2 boards listed incorrectly.

There’s only one Raceboard fleet in Sydney (Dobroyd on Iron Cove) and one in Wollongong, with a small scattering in other states.

BTW on general dinghy design (as discussed above) I’m not sure that ANZAC design has lead the way as much as is often assumed. For example, the National 12 was miles ahead of Australian designs in adopting the U sections seen in most high-performance modern craft. We haven’t had a world’s winning design in 14s, for example, since the Northern Hemisphere and Aussie classes were unified. The mylar-sailed Tasar now seems to be pretty much back on a par with the NS14 in terms of pace (judging from the last two regattas where significant fleets raced) yet the National 12 apparently regularly beats Tasars in UK conditions despite being almost 3′ shorter.

As always, Mike, you write with a great deal of knowledge about small boat design. However, I would like to provide some input about windsurfer efficiency.

Seen in the same terms as a non-foiling dinghy – i.e. their all-round speed around a conventional course in a range of winds – the boards are definitely efficient for their LOA and SA. There are actually yardsticks that are pretty reliable. They rate the Raceboards (3.9m, around 9.5m of sail) at a similar pace to the International Canoe (5.3m-ish, 10m of sail) and from about 8 knots that’s under-rating the pace of the board. In 10-12 knots or so the board is toasting the IC upwind and downwind.

Similarly, the Division 2 boards (3.9m, 7.4m sails) out-paced the pre-foil International Moths which had fewer rule restrictions. I don’t believe the extra length of the round-bottomed D2 boards was a significant factor as D2 design had moved away from maximising LWL. From about 8 knots the board was considerably faster,from my racing against the world’s best 2 Moths, and again the board is quicker than the Canoe from around 8-12 knots.

While these speed are definitely not in the realm of the foilers, they are notably quicker than the best of the conventional boats of similar dimensions. Just a minor point but you are so accurate on this stuff I thought I’d mention it.

Grrrr, I hate to be wrong, but I’m glad for the correction.

In a way, my numbers, taken from the yardsticks below agree completely with what you say – so don’t think I was too far out – but certainly my EMPHASIS was out!

My big sin was, I think this

The thing about the moths is their EFFICIENCY. Sailboards are not even close.

If the sailboards are being compared with the pre-spinnaker international canoes – then I think there is some validity in what I say. The canoes are brilliant boats upwind and reaching, but on turning onto the running leg in light or medium weather also became nothing special – just another dinghy. So to compare the sailboard probably admits there are some holes in its performance too. Whatever the canoe or the sailboard might do in the right conditions to a more complex but fast boat like a 505.

Are the yardsticks reflecting this available, I looked everywhere!

I did a check on your email address and found activity on the Taser IC and sailboard furums. Useful thing Google!

Of the sailboard class with the best performance, what is the basic configuration these days? Volume, width, board weight

Are centreboards still used on raceboards?

Also where are the competitive Raceboards fleets around Sydney these days?

Follow up – I had a good look around to see what has happened with sailboard design. It seems that it has largely stagnated with boards like the Lechner and the D2s being quoted as being reasonable examples. The big developments that have been made have been with sail design – with boards being able to carry 9.5m sails through to surprisingly high windstrengths, when I remember a decade or more ago that they were struggling to carry 7.5 square metre sails.

It might be fair to say that my assumptions, partially drawn from Bethwaite is that the sailboards have been too limited by a lack of righting moment (no trapeze, leaning planks or stilts!) have been overcome to some extent as evidenced by the bigger sails. Though I haven’t read the revised version of his book “High Speed Sailing” since the first editions.

Well, as far as them going around the harbor at 25 knots, it couldn’t be worse than the jetskis at 50 knots ;)

Actually I have thought at times about taking one of the square boats like the Oz Racer or the Goose and adding foils. Those nice square corners just cry out as attachment points for foils…..

Of course to complicate matters, I would want to make foils that are tubular much like ducted fans but no mechanicals. Either that or the ladder foils that loose lift as they emerge to focus on stability rather than speed.

Haha – any mindless fool can BUZZ BUZZ around the harbour on a jetski – but when it comes to it – they drive similarly enough to a car with some sideslip. But a sailing boat – I can imagine someone thinking they can blast across in front of a Manly Ferry, not realising that they are gradually pinching the boat and find they are dead stopped in front of the Ferry. Or cannoning into another boat when a gust hits.

The thing about foiling is that every contrivance will crash to earth occasionall. With the big flat area of the PDR I would recommend getting your foiling photos early in the piece incase of a fatal crash later. Fatal to the big flat sections of the PDR!

The ladder foils would be more tolerant as there is more that has to ventilate for you to lose lift completely – whereas when the T foils suck air down from the surface they just lose the lot.

Doesn’t seem to worry the moths too much – before the foils they would sail happily at 15 knots or so – which is very fast for a monohull. A PDR hull might be a bit at sixes and sevens hitting the water at that type of speed!

I think you could go broke trying to sell reef points in OZ.

Maybe some day they will make something with lifting foils for us old folks just to make for a nice smooth ride instead of banging into chop.

Haha – we are an embarrassing lot really!

That’s the reason we put so much sail on the OzRacer/OzPDRacer – as a sort of antipodean joke.

And were we surprised when we found the boats had enough stability to carry it easily!

I think there is space in the market for something simple to sail but foiling. The company that makes the ’49er class dinghy, Starboard Products, has produced some very fast experimental boats, but they have been worried about putting them on the marketplace because they are not sure that having inexperienced sailors zooting around the harbour at 25 knots is such a great idea!

Your point about bangin’ into chop is a great one. Have a look on youtube at some of the big multihulls going fast in a seaway and then compare to Hyroptere – the similarly sized foil tri – it looks as smooth as silk in comparison – though every one is on edge.

Well, before this thread gets too long…

In general, I get the feeling that you enjoy the open class developments. The experimental stuff that may be a huge step forward or a non-starter but still a valiant effort.

I’m quite sure that when the first Moths started flying, they were just a strange oddity until they got everything sorted out. But one huge difference is that they continue while the other foilers such Hobie Tri-Foiler and the Windrider Rave just make a curious historical footnote. Do you think that the closed nature of just being a pre-packaged solution and not open to tinkering killed them off or just the fact that they were too expensive to get adopted on a larger scale?

Is it that someone gets a good start but without the gestalt of other people picking and improving, it stagnates?

Why do you think that some designs fall flat? A perfect example in my opinion is the Adventure Trimaran 24. I look at this video

http://www.youtube.com/watch?v=echGgGtE424

and see it as just stunning as it ghosts along. But in the other videos out in real wind in pretty modest sailing conditions, it does fine but nothing to particularly commend it over any of the other multi-hulls.

Very well observed David – and I have no fear of this discussion getting too long – it is great.

The Moth has moved a bit away from its roots. It was a constructor’s class until recently with teams of expert and less expert builders making boats in the off season out of sticks and glue.

It has few restriction. Hull Length 11ft Sail area 85sq ft (sorry – I am not metric with sail areas) Maximum height of sail above deck – 18ft No hollows in the hull shape (to prevent catamarans) No minimum weight, minimum beam

During those days the moths were very potent for their cost and size.

The scow moths of Oz – this one was the only one in the 2011 worlds in Oz – and is just stooging around before the start – it is a late ’70s design, before the transoms went narrower for better downwind control (mentioned in the comments above).

And the skiff moths of the UK (nonfoiling at that stage) – the pici is of John Claridge – one of the guys who made the skiff moths very competitive with the Australian Scows (finally).

… fought it out for dominance for decades – and resulted in the most sophisticated lighweight construction – 0.7mm (1/64″) hull skins and bulkheads and the cockpit out of 1.2mm with very light glass under. This was aircraft type construction – true monocoque skin supported by light western red cedar stringers.

Not for everyone either – but it showed what is possible. The scow hulls were about 34lbs without fittings. They ended up with a performance yardstick similar to the International Contender – 50% longer and 50% more sail.

This is the Contender – a puny 11ft boat can sail equal with that – it is pretty similar to the Paper Jet we discussed earlier in term of hullshape technology. Don’t get me wrong – the Contender is way fun to sail too.

A triumph of efficiency over sail area and length.

In the end the skiffs went really narrow – and that’s when they started to become superior to the scows. They tended to nosedive though – so inverted T foils were put on the rudder – so when the boat goes nose down the forces developed by the rudder T foil pull the stern down so the boat stays in trim automatically.

The next step was the trifoiler – think Hobie Trifoiler but with the weight and complication and expense wrung out. The minimal approach really defines the Moth.

Hobie trifoiler followed by a trifoil moth pic

That was the mistake of the Hobie trifoiler – it was big, complex and expensive. The little trifoiler moths were quite easy to sail (apart from the occasional crash off the foils) and represented a rooftop package weighing little more than 90lbs all up. However they were considered too easy to sail. Suddenly a class that was considered to put a premium on handling and skill could be sailed by geriatrics. They were in a quandary.

One of the main drivers of the DIY wooden moth development was a Sydneysider – Ian Ward. He demonstrated a bifoiler (two foils only) after being told it was “impossible to balance” – two foils only concept – was possible to sail by parading up and down in front of the sailors at the Seaforth Moth Club (I think that is the story). The foilers are easier to sail than the non foiled narrow moths, but very difficult to sail well.

Originally the hydrofoil moths would race amongst the conventional boats at the worlds – would win one or two races by miles but the rest of the time not look very special. This is exactly had happened when the very narrow skiff moths were developed too (in the UK). The first generation bicycle configuration Moths would only fly reliably in 10 knots of breeze.

I saw some racing from a distance at the beginning and you would see one of the few foilers jump out of the water and disappear into the distance, then drop back into the water and the other boats would catch up.

But week in, week out racing has changed all that. They now fly in quite light breezes – about 5 knots of breeze. This is not HALF of 10 knots – the power available in a 5 knot breeze is only 1/4 of that in 10 – showing how far the boats have come. All sailors gybe without falling off the foils and some of the better sailors can tack without falling off too.

So to the trifoiler (and windrider) – it was too big, too heavy, too complicated to rig and unrig and very expensive. The complexity led to unreliability of the structure. How could it succeed? However it pointed the way. I was gobsmacked to see one on TV just turning circle after circle. Prior to this hydrofoils (apart from the little speed week cat “Mayfly” – another important step) were touchy and difficult – But Russell Long brought something new into creation – you could sail in circles all day and anyone could sail it. But every step of production added more and more complexity.

You need some pressures applied externally to be minimal – the moths are restricted by maximum sail area (it is not big) and no minimum weight – so huge pressures to simplify.

The pressure on the Moths from the start has been to do things in the simplest, most minimal way – you just need to look at the fittings on the boats to see that. Bits are “lashed on” with carbon roving soaked in epoxy. They have lost the low cost of the wood boats – but some of that thinking still holds on – but I think they are still justified because of the almost harrowing speed of development.

Here is a brochure for a 420 dinghy – a standard fibreglass racing dinghy used for international competition. It is great for regattas, but its performance is a bit “old hat”. The full price to get one on the water is similar to the cost of the Moth – $16K compared to $18K. I know which one I would have been sailing at that stage of my career.

They start looking a bit sick when you realise that wooden moths could be built for about $2000 now – still very fast boats for their size.

I do regret the “build a boat during winter” approach has been lost – the loss of that might mean that Moths head for more and more expense, rather than just costing a plywood, epoxy and timber budget – and 35lbs of that doesn’t cost much. So far they are reasonably priced as a full carbon production thing compared to boats of similar performance and many of much less performance. – but that will tend to stagnate development – instead of 20 home builders creating slightly different boats, we have to wait for two or three manufacturers to do some development.

Moths would have been impossible without “Mayfly” or the “Trifoiler” so give credit where credit is due. But the open-ness of the class and the rule pressures to make things minimal have been a potent cocktail to make Moths the amazing boats they are.

photo sets on Flickr

And here is the Moth’s own viewpoint of their development

Michael, Could you provide or tell me where to find some more information on the trifoiler Moth? I am very interested in constructing one as it seems much simpler to construct and sail than a “normal” foiling Moth.

I would make enquiries of the Moth Association in Australia to see if they can direct you to someone who can give you some information.

They also have a good website and some of the state websites and their old website has considerable information … maybe you can join their chat forum (ask them) and see if anyone has info they can share.

I am pretty sure most of the trifoiler development was manufactured stuff. I don’t know if there might even be some parts for sale.

Main thing is that whatever it is attached to has to be pretty light – I think Moths were around 80lbs all up in that era, and also a fairly fast intrinsic hullshape so that when you crash off the foils the hull can kinda keep on sailing.

http://www.moth.asn.au/

HOpe this helps Michael.

I am curious though. I wonder how the total weight of the mast and standing rigging is compares to a free standing rig. I realize that these Moths are under a different set of constraints (and not designed for all around sailing.) They are cool in their own technologically interesting way but pretty much just an obscure offshoot much like hovercraft.

You can get one person moving faster across the water with a wind surfer or a sail board and not spend 18K. I think that what you make with your high performance boats such as GIS (although it is cunningly disguised as a “Traditional Boat”) makes a lot more sense. Lower cost barrier for entry. Sails in a wider range of conditions. Doubles as a party boat when you put more people aboard.

I think much more interesting than the Moths are the little PaperJet 14 from Dudly Dix ( http://www.dixdesign.com/paperjet.htm ) The three rig options make it something you can grow with or play with different groups. I know there are others in that genre but these are cheap and readily available. Under 1K in kit form is much more reasonable than the 18K for the Moths. Could possibly have it on the water under 3K.

I still think the GIS is a nicer option since you can also carry people and not just a 1-person toy. Not to mention simpler rigging.

Howdy David,

The Paperjet is a fine little boat, but it doesn’t do anything particularly new. It represents something similar to the plywood boats in OZ from about the 1980 era – though the Paperjet construction method is much, much better sorted out. I would still recommend it as a boat to consider for many sailors.

Since that time there have been very big discoveries about what makes small boats fast but easy to handle. Starting from the mid 1980s in the Moth class where they found the scow type would eliminate nosediving if they made drastic changes to the shape of the stern – before that they thought they had to do something at the BOW to stop it from digging in. This happens to be true for multihulls as well – adjust the back half of the boat and you can prevent much nosediving.

It is the same reason canoe sterned boats have a better reputation for seaworthiness – about distribution of hull volume, rocker (and in a yacht the aft buttock lines.

From the scow moths it went to the skiffs and then restricted classes like the NS14 and Cherub. The Goat incorporates that thinking and it can heel to very high angles and still steer reliably – something the pre 1980 hullforms won’t do.

A second area is planing behaviour – the experience of these new hullshapes can be a surprised to very experienced sailors (unless they are sailing an Oz or NZ derived design like the Olympic 49er. This is from Michael McNamara who makes sails for some of the most competitive classes in the UK about sailing the Goat. This is what he wrote to Ralph Gersson in the Netherlands.

I had a nice long sail in Richard`s Goat Island Skiff today and had a lovely sail. He has made a great job of the boat and it went like a dream. I was very impressed with how simple the controls were and how quickly the boat went. It was also beautifully balanced . As you could expect the boat felt better when it was slightly heeled when beating. Off wind it felt fast but didn’t create a planing sort of wash…it just went faster and faster . When tacking I found that I had to be quite forceful in pushing it into the wind and it was definitely better to “roll” it coming out of the tack.

The highlighted words are exactly what has been worked on in OZ – playing with rocker, volume distribution and effective hull bottom width.. Looking at the way the National 12s are sailing in the UK – they are using the same methods and it is spreading to other classes where there is freedom to change the hull shape. Interestingly the big high speed yachts like the supermaxis and Open60s are still oblivious to how much better their boats could be. You can keep up higher speeds in marginal planing conditions because the boat transitions through to planing much more easily and you can push closer to the edge and know you can keep control with much less rudder effort.

OK – Moths.

Years ago on Sydney Harbour they had a race between C-class Catamarans (the full wing Miss Nylex), Tornados and 18ft skiffs. The C-class cat came first, the 18ft skiffs came second and the Tornados were shocked to find that they came third.

A sailboard would not be in the hunt because their upwind performance is so poor and their dead downwind performance requires much longer distances than the others. The others can go deep. On a reach a sailboard comes into its own, but upwind and down or in rough water they are nothing special. Actually, I exaggerate – they ARE special, but are let down by performance in particular areas.

I agree partially with your argument about cost – but by the time you put a sailboard together with the different rigs and accessories it is going to be a good proportion of the $18K for a Moth. And its never certain whether you need the longboard or a high volume shortboard for light winds or if you need the low volume shortboard for over 10 knots. Might end up being much more expensive than the Moth if a sailboard sailor is looking for best performance in all winds.

I will back this up with data.

So lets look at performance of a few boats around a regular racecourse. The Portsmouth Yardstick is based on actual performances averaged around real racecourses using real boats. Check the current Portsmouth yardsticks (PDF) (note the Moth has two figures – foiling and non foiling versions)

Tornado – two person catamaran – 20ft – 643 A-class cat – 1 person singlehanded – 18ft – 690 (very highly developed because of a lack of restrictions in design) Hobie 16 – two person beach cat – 802 505 – International trapeze racing dinghy – 16ft – 902

There is no official number for the sailboards I could find, but from pursuit races in the UK the sailboard people themselves were giving numbers close to the 505 – which is pretty good – perhaps a little optimistic, but let’s accept their figure… Raceboard class – 902 approx

Moth – 690 This is a serious breakthrough – around a course 30% faster than the best normal dinghies and sailboards and equal with the best singlehanded cats.

A sailboard can go faster in a 50ft wide trench down in the tropics with wind from the perfect direction – but put the same board on an upwind downwind course in a normal chop and it won’t be able to get to the top mark – too specialised with a narrow band of efficiency. Moths have full sailing performance with efficiency on all points of sail. Even non foiling they have close to the upwind speed of the Goat Island Skiff, sailed hard and 4.5ft longer.

I agree the particular solution is not for everyone!

In some ways it is still early days for Moths – but the intensity of the racing (over 100 boats at the worlds) will probably mean more big jumps – extending the takeoff speed ever downwards and reducing the “crash and burn” in really rough water. The price at about half of a high performance two person dinghy has meant a serious growth in the fleet and the countries sailing. Ten years ago there would have never have been participants in the Moth from the USA, China, Sweden.

It really is a big jump in many ways. But as you say – not for everyone!

Best wishes Michael

I think the biggest problem to using these kinds of rules of thumb has been over specialization. You have three competing goals that have to balance out: the Designer, the Engineer, and the Builder. Each of them off isolation make bad decisions for the others. In a modern context, they are all different people and may not even normally work together. The Herreshoffs are a perfect example of when it worked well. They were a one stop shop. You got the designers, the engineers, and the builders in one package that all worked together and understood their roles and were able to accommodate each other.

The Engineer wants to build in more and more reliability and the overall design and build considerations are secondary. They want to calculate everything, whether it can even be calculated or not, and are resistant to making extraordinary leaps by deviating from standard practice.

The Designer wants to make their ideas real. Let the other people do all the real calculations and figure out how to make it. There is a lot of “eventually the technology will be available.”

The Builder is looking at cost and how to actually put things together. They know what the materials really cost and understand the reality of what the materials can do in a practical sense rather than a theoretically.

In the limited context of boat building, the Engineer is in trouble. The environment is dynamic and chaotic. Only recently with high performance computing has it even been thinkable to try to accurately model what forces are involved even in one static scenario let alone in all conditions. Sometimes all they can do is make a guess and see what has worked before and maybe try some tiny deviation.

The Designer always has the handicap that they are trying to divine what the customer wants and it can end up being akin to working with an Ouija board. They tend to follow what everyone else is doing. Kinda like the car designers putting fins on cars.

The Builder is constantly confronted with new materials that they do not yet understand and the rest of the materials are full of flaws and variations. Many of the newest materials are so unknown that about all you have to go on is the advertising copy from the manufacturer and they are afraid to put down hard information because they think everyone will sue them. They also get the blame with things go wrong. The Designers and Engineers just fold their arms over their chest and say they were right and the Builder just didn’t follow their specifications.

About the only time these three competing egos can agree is when they are the same person. Even better if they are also the customer and will take responsibility when they get it wrong. The real magic happens when these conflicting entities balance out and create a really special outcome.

Nice essay in reply David,

I think the problem is more with the idea that there are simple solutions that anybody can use. There are some, like the gluing area example I gave that are highly useful to anyone building a boat. But then most go too far.

For example I just found out that the figure that the centreboard has to be 4% of the sail area is from Marchaj – a very respectable source – but experimentally based – but I know from experience it is wrong as a general rule. You just have to look at model yachts compared to maxi yachts to see that it is not a practical solution.

I will have to have a closer look at Marchaj and see the exact wording and methodology that he used before commenting further.

Part of the reason the model yachts have a deep keel is that they have less stability and the weight needs to be placed lower down – but it doesn’t explain how wide the keels are in comparison with real yachts – or how a very good bunch of sailors can make a boat with a tall skinny keel fly really well, but a bunch of amateurs make it sail like an old sock! I know why – it is idea of keeping up speed so the narrow keel can “fly” all the time – never try to sail high before hitting critical speeds for the windspeed and sea conditions.

The practical differences can also be practically observed in the difference of behaviour between an 8ft boat and a 16ft boat. The 8 footer needs much more area in the centreboard/leeboard in comparison and the sail area is only a secondary effect.

Anyway – going to your points – it is all about knowledge. The “Engineer” and the “Designer” will agree with the above and tell the “Builder” what to do.

Like you say the problem comes for the “Builder” when they have no access to the thinking of the “Engineer” or “Designer” – and that of course is where a good plan comes in very useful – something I try to use as a tool to increase the knowledge of the builders so they know WHY the “Designer” and “Engineer” tend to be relatively inflexible about the big things. This might seem like a restriction, but if the builder accept the knowledge presented then they can make educated steps of their own in their own future projects. That is something I work rather hard on in my forum, emails and general internet activity. If people UNDERSTAND they will do brilliant things on their own.

I would be the last to suggest that builders should not experiment, or that inexperienced people should not design their own boats – but they do need to be very objective if they want to learn.

The best thing for them is the objectivity of entering some races.

There are many websites now that say how easy it is to build a carbon mast, or build a solid wingmast for a little boat or using carbon and plywood to make a stiffer hull “sandwich”

They all say how good their boats are. However with examination we find out their carbon mast is heavier than a wooden one because they started with too small a diameter, or the wingmast boat can barely sail out of its own way because the hull design is so bad and the wingmast so heavy or that the carbon/plywood sandwich is less stiff and heavier and WAY more expensive than using the next plywood thickness up.

Great things to have on the net – but not an objective point of view – and they become some sort of standard because they are widely read and discussed.

For example I would trust information from the Moth or UK Cherub websites about mast making – because of the sharing of knowledge and continuous improvement in racing classes, but very much more doubtful about an amateur working at home in isolation and appearing to have done little research about how much a timber mast or a carbon mast SHOULD weigh.

That’s where my comments are directed – a certain reality comes by observing the scene in a broad way – to try to make generalisations about the “best practice” and getting your boat out into company to see how it goes.

I will leave with a pic of a rig developed my friend in Texas, John Wright. He is an experienced sailor and amateur builder – and a great seat of the pants designer. He developed this rig from a standard telescoping pole and all bits for the sail and rig fit in a 4ft long bag. The boat itself is a ply/foam sandwich – a brilliant bit of industrial design – that weight in around 35lbs (16kg).

He developed this rig – which most won’t realise, but it is actually closer to the classical “Junk Rig” than anything else. But he sailed it with the other Puddle Ducks at the Georgia world a couple of years ago. Here he is racing it around the course with the other puddle ducks – a great test! He ended up finishing mid fleet after three races and was improving with more time with the rig. It’s never going to be a world beater, but nobody else could put their entire rig in a bag without use of an axe!

This kind of stuff is brilliant – and it makes sense to choose a simple platform of similar boats like the ducks to experiment with.

I think that another problem that you touch on is the infatuation with seeing some materials as more glamorous. Similar to the carbon fiber mast versus a wooden mast example, one really eye opening experience was watching a video by Matthias Wandel demonstrating his home built bandsaw design ( http://woodgears.ca ). He hooked up a dial indicator and hung his weight on the arm of the wooden home built saw and did the same with his cast iron saw. The wooden bandsaw had about half the deflection as the cast iron version.

Which do you think is a bigger problem, the people that jump into new materials just because they are new and sexy or the people that hang onto more traditional materials just from nostalgia?

A good example would be the short reign (in a historical sense) of metallic rigging on boats. For most of history, it was fiber lines, then everything converted to steel, and now we are back to fiber lines with dead-eyes being the avant garde.

I know the history of why the plywood tradition was developed so strongly in your part of the world. For the rest of the world, do you think plywood will overcome it’s stigma? Do you think that fiberglass hulls will follow steel rigging into history or will the ability to build “good enough” boats with relatively unskilled labor blowing it into molds will keep it going?

I think the answer to excessive nostalgia or progressiveness is to keep up to date about the past, present and future and be able to see what each can do.

For example the state of the art masts for the Moth Class boats are made of carbon and have a diameter of slightly less than 40mm. In the days of aluminium masts the diameter would have been about 50 mm.

Timber spar diameters are generally about the same as alumimium but with a much greater wall diameter. I only know this because of experience of all three including design and building. The moth experience is very recent – just a couple of weeks ago. I had an invitation from a Goat Island Skiff builder to go and view the Moth Worlds at Lake Macquarie. This sort of experience of seeing state of the art information applied in a competitive environment is hugely useful.

The moth pics I took are quite detailed about some of the bits – I was quite surprised at the mast sizes though. This is my car key beside the mast.

The 2011 Moth World photos are here . Another great resource is the UK Cherub website .

I know from our database of spars for Goat Island Skiffs that a properly designed wood spar is about 16lbs but a carbon spar is about 6lbs. This would be a guideline for comparison between any other freestanding mast – that the carbon should be about 1/3 the weight of a timber mast.

The general idea is to observe and be able to do a bit of math.

The plywood tradition here is actually fairly dead now except for those of us who were involved. When the racing classes finally allowed foam (and other) sandwich constructions then ply was outclassed – in some classes very eventually – but it happened eventually.

The low hull weights we were getting with ply (8 to 10lbs per hull foot – or Moths in the wood era an amazing 3lbs/foot) are still maintained but the sandwich allows greater panel stiffnesses – but has lost the simplicity of single skin glass construction – which was the big advantage of the technology.

I do think there are places for boats of all constructions. People who are really interested in materials will attempt to be quite objective and take the maximum from every opportunity they get to learn more.

One recent one for me was the Goat I watched the Moth Worlds in had a hull weight of 105lbs (6.8lbs/foot) because the builder had used Paulownia timber for a lot of the framing. It is between cedar and balsa in weight and there was a little concern about whether using it to hold the ply would subject it to too high splitting loads, but Bruce has sailed his GIS is all sorts of nasties in the last 6 months and the boat is absolutely fine.

It stood up to a full planing crash onto a sandbank with two aboard which threw both of them over the front of the boat with only tiny damage to the centrecase – a great indicator of just how strong the daggerboard setup is.

So I have learned even more!

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ABS Yacht Rules & Plywood Construction

Discussion in ' Class Societies ' started by F83MGM , Jun 19, 2024 .

F83MGM Junior Member

Looking to the brain trust for some clarification.... I see a lot of plywood construction in the industry I'm working in and I'm looking for confirmation (other otherwise) that I'm using the correct formula for plywood structure in the ABS Yacht Rules. See: New Fluid Topics Tenant https://pub-rm20.apps.eagle.org/r/15/2024-01-01/Yacht-Rules Reference Section: 3-2-3/7 Wood, Cold-Molded Laminate and Carvel Thickness calculations for plywood structure, does that fall under 7.3.1 Cold Molded Laminate Thickness? Is plywood considered cold-molded laminate? My (very limited) understanding is that 7.3.2 Single-Skin Carvel Construction refers to what I would call 'planked construction'? We're moving away from the 1978 Glass rules (sad face...) and the Yacht Rules, under ABS, are the closest reasonable facsimile for the fleet in question. Humbly submitted!

skaraborgcraft Senior Member

I have been using Gerrs scantlings as a guide, so can only offer his interpretations of a boat with the same SN for plank on frame. Traditional plank 16mm Cold moulded 12mm Plywood 14mm (90% of trad plank thickness on topsides but equal to plank thickness on bottom) Frame spacings can either reduce or increase skin thickness.

TANSL Senior Member

I'm sure that's what Gerr says but, honestly, I can't find any technical explanation that justifies these "equivalences."

Lots of people think plywood should be thicker than plank, as it only has half the strength in one direction, certainly multi laminated cold moulded can have better strength in more directions than plywood, so can be thinner for the equal strength and thinner than plank. I heard Gerr used a combination of recommended scantling authorities, and averaged the findings. I dont know if that is accurate, but it would seem a logical thing if you can further break it down to a displacement figure. Certainly many plywood boats on the 60s where built with much thinner material than "plank", but they often did have a more extensive framework. Im sure there is no end of test videos on youtube. The thing with plywood is the gap between thicknesses, some people size up with a weight penalty, and some will size under. With plywood you buy a product, with planking you can mill to specific size if a scantling authority demands it to meet some class classification. Slapping fibreglass on plywood to make it stronger, usually ends up with a heavier skin than if one used the larger plywood to start with.

DogCavalry Senior Member

TANSL said: ↑ I'm sure that's what Gerr says but, honestly, I can't find any technical explanation that justifies these "equivalences." Click to expand...

DogCavalry said: ↑ If you made an effort, you would find those explanations, so it's disingenuous to say you can't. Click to expand...

Again, since you haven't read his long detailed description of exactly how he did it, you can hardly suggest he hasn't provided a "technical" explanation. You just don't know.

Perfect, @DogCavalry . I agree with everything, are you happy? Edited : Ok, I was wrong and I will try to prevent such a mistake from happening again.

DCockey Senior Member

From Gerr's description of the origin of his scantling system: https://www.gerrmarine.com/ELEMENTS_OF_BOAT_STRENGTH/BoatStrengthIBEX.pdf How the Sn Scantling Rule Was Created Where does one start to create a scantling rule? With real boats. We’ve already seen how difficult it is to know what the real loads are on a boat. What we can know with good certainty is the specifications of boats that have been built and have given good service over many years— dimensions, displacement, speed, type of service, material, and scantlings actually built to. These data can be analyzed (regressed) to obtain the desired rules. The data and the results are constantly checked and rechecked against other real-world boats, against basic class rule results and against first principles. With any such process, the results are not going to and should not match any other specific rules’, or methods’ results, but the scantlings from the resulting new rule should produce consistently reasonable structures, that meet reliable criteria for strength. The real boat data available to work with came from: - My own designs actually built and in service (and from the MacLear & Harris office and from Cape Dory Yachts) - Boats from other designers for which I had data - Boat data from the three-volume set of Fishing Boats of the World - Additional wooden boat data from USCG NVIC 16-60, Scantlings for Wooden Passenger Vessels This totaled hundreds of different vessels as a reference database. Results were checked against: - Engineering by first principles - ABS - Lloyds Again the goal was not specifically to meet any of the class rules, particularly given the unknowns in loads, but to be close on the majority of the structure. One of the interesting findings was how strong many real-world boat structures actually are, even without meeting the requirements of class rules. Stiffness and strength in real boats, often are considerably greater than such rules might indicate. Previous thread about Gerr's scantling system: Dave Gerr Boat Strength Scantling https://www.boatdesign.net/threads/dave-gerr-boat-strength-scantling.60880/

gonzo Senior Member

skaraborgcraft said: ↑ The thing with plywood is the gap between thicknesses, some people size up with a weight penalty, and some will size under. With plywood you buy a product, with planking you can mill to specific size if a scantling authority demands it to meet some class classification. Click to expand...

Design to an specificity greater than 3mm would be an exercise in pendantic self deception anyway. Multiplying an approximation by an estimate, and dividing by an average and insisting on taking the answer to three significant digits because you'd done the math correctly.

@DCockey , I greatly appreciate your effort copying paragraphs from Dave Gerr's book but it is not necessary, at least on my part, for you to work so hard. It is enough for you to tell me the page you want me to read and I will read it. That said, I reaffirm in the comments I made in my previous post, not a single technical justification for the SN (I understand, but you can understand something else, that an accumulation of data from many ships is not technical reasoning). I recommend that you read the note at the bottom right of page "ii", the one before the "CONTENTS" chapter. As I greatly respect all the members of this forum, I don't want to bore them by copying that NOTE here.

TANSL said: ↑ @DCockey , I greatly appreciate your effort copying paragraphs from Dave Gerr's book but it is not necessary, at least on my part, for you to work so hard. It is enough for you to tell me the page you want me to read and I will read it. Click to expand...

DCockey said: ↑ I am not making any statement about the applicability or validity of Gerr's book. Click to expand...

gonzo said: ↑ Plywood thicknesses vary by 1/8" (~3mm) so the weight penalty is minimal. Click to expand...

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Luxury yacht interiors and the creative process behind

The Art of Interior Design in Yachts: Exploring the world of luxury yacht interiors and the creative process behind designing them.

Step aboard and immerse yourself in the opulent world of luxury yacht interiors! From sleek modern designs to timeless elegance, the art of interior design in yachts is a captivating blend of style, functionality, and creativity. Join us on a journey as we explore the top trends, layout tips, material choices, furnishing styles, and clever storage solutions that make these floating palaces truly spectacular. Get ready to be inspired by the beauty and innovation behind crafting the perfect yacht interior!

Top trends in luxury yacht interior design

Luxury yacht interior design is constantly evolving, embracing new trends to create stunning and functional spaces that cater to the desires of discerning clients. One notable trend in yacht interiors is the use of sustainable materials, reflecting a growing awareness of environmental responsibility within the industry. Another popular trend is the incorporation of smart technology, seamlessly integrating features like automated lighting and climate control for enhanced comfort and convenience.

In terms of aesthetics, contemporary minimalism continues to be a favored style among yacht owners, with clean lines and neutral color palettes creating a sense of calm sophistication. On the other end of the spectrum, there’s also a resurgence of classic glamour in yacht design, with luxurious fabrics, ornate details, and rich textures evoking a sense of timeless elegance on board.

From innovative layouts to cutting-edge decor elements, staying ahead of these top trends ensures that luxury yacht interiors remain at the pinnacle of sophistication and style.

Superyacht Luxury Interior Design Fitout 1

Material and design choices for yacht interiors

Choosing the right materials and designs for yacht interiors is crucial in creating a luxurious and stylish space that reflects your personal taste and lifestyle. From opulent marble countertops to sleek stainless steel fixtures, every detail contributes to the overall aesthetic of your yacht’s interior.

When it comes to materials, consider durable yet elegant options like teak wood flooring or leather upholstery for a timeless look. Incorporating high-quality fabrics and finishes will not only enhance the visual appeal but also ensure longevity in a marine environment.

In terms of design choices, think about maximizing natural light with large windows or incorporating innovative lighting solutions for ambiance. Selecting a color palette that complements the ocean views can create a seamless connection between indoor and outdoor spaces.

Whether you prefer modern minimalism or classic elegance, the key is to balance functionality with aesthetics to achieve an inviting and sophisticated yacht interior that suits your unique style preferences.

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Popular interior styles for yacht furnishing

When it comes to interior styles for yacht furnishing, there are a few popular options that exude luxury and sophistication. One classic style is the nautical theme, featuring navy blues, whites, and touches of gold or brass accents to create a timeless maritime ambiance.

For those seeking a more modern look, contemporary design with clean lines and neutral colors like grey or beige can provide a sleek and elegant aesthetic onboard. Incorporating state-of-the-art technology seamlessly into the design can elevate the overall experience.

Alternatively, an eclectic style mixing different textures, patterns, and colors can add personality and vibrancy to the space. Think bold artwork pieces paired with plush velvet furnishings for a stylish yet cozy atmosphere that feels like home away from home on the open seas.

No matter which style you choose for your yacht furnishing, creating a harmonious blend of comfort, functionality, and aesthetics is key to achieving a truly luxurious onboard experience.

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How to design the perfect layout for your yacht

Designing the perfect layout for your luxury yacht is a crucial step in creating a comfortable and functional space that reflects your personal style. Start by considering the flow of the space – ensure there is enough room to move around freely without feeling cramped.

Think about the purpose of each area on the yacht – from dining and lounging to sleeping quarters and entertainment spaces. Each area should serve its own unique function while seamlessly connecting with the rest of the layout.

Utilize natural light to create an open and airy feel onboard. Large windows, skylights, or even glass floors can bring in plenty of sunlight and offer stunning views of the surrounding waters.

Consider incorporating versatile furniture pieces that can easily transform to suit different needs throughout the day. Opt for sleek designs that maximize space without compromising on style.

Lastly, don’t forget about outdoor areas! Designing a seamless transition between indoor and outdoor spaces will enhance your overall yachting experience as you enjoy breathtaking sunsets or dine al fresco under the stars.

Clever storage solutions for yachts

When it comes to designing the interior of a luxury yacht, clever storage solutions are key. With limited space on board, maximizing every inch is essential for both functionality and aesthetics.

One smart storage solution often seen in yachts is utilizing hidden compartments beneath seating areas or within walls. This not only saves space but also maintains a clean and uncluttered look throughout the yacht.

Another popular option is incorporating multi-functional furniture pieces that serve dual purposes, such as a coffee table with built-in storage or a bed frame with drawers underneath. These innovative designs help minimize clutter while adding practicality to the living spaces.

Vertical storage solutions like tall cabinets or shelving units can also make use of otherwise wasted space, providing ample room for storing belongings without sacrificing floor space.

Overall, integrating these clever storage solutions into the design of a yacht ensures that everything has its place, creating a harmonious and organized environment for passengers to enjoy their time at sea.

Luxury yacht interior design is truly an art form that combines creativity, functionality, and elegance. From incorporating the latest trends to selecting the perfect materials and styles, designing the interior of a yacht requires careful planning and attention to detail.

By following top trends in luxury yacht interior design, creating a layout that maximizes space, choosing high-quality materials and stylish designs, as well as implementing clever storage solutions, you can transform your yacht into a luxurious floating oasis.

Whether you prefer a modern minimalist look or a classic nautical style, there are endless possibilities when it comes to designing your yacht’s interior. So let your imagination run wild and create a space that reflects your personal taste and lifestyle while enjoying the ultimate luxury on the open seas.

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The America's Cup: Everything you need to know about the sailing competition

Ahead of the 2021 America's Cup in New Zealand , Elaine Bunting explains everything you need to know about the sailing competition in our handy guide - from America's Cup racing rules and history, to detailing just how fast those hydrofoil boats can go...

The America’s Cup is considered the pinnacle of yacht racing. Every four years, teams compete for the oldest trophy in international sport in yachts that represent the cutting edge of yacht design and technology.

This is a magnet for the world’s most talented sailors. It is notoriously difficult to win, and the opportunity comes only once every four years. Yet the storied history of the Cup has always attracted brilliant minds and been backed by some of the world’s most ambitious and successful businessmen.

The America’s Cup match is held between only two teams, the defender and one challenger. The series that establishes the right to be that challenging team was held through January and February, and provided some genuinely shocking moments.

WHAT HAS HAPPENED SO FAR?

Two of the four challengers were eliminated in the Prada Cup challenger series in January and February. The US team American Magic spectacularly spun out of control and capsized in a high-wind, high-speed mark rounding. Despite rapidly being rebuilt, the team was unable to get the boat fully functional again and was ousted from the Prada Cup without a single win.

The British team INEOS Team UK, led by Sir Ben Ainslie, won the opening round robin series handsomely and were regarded as favourites only to shock fans when they were thrashed 7-1 in the Prada Cup final by the clearly faster Italian team Luna Rossa Prada Pirelli.

So after several brutal gladiatorial rounds, the match is on between old rivals Emirates Team New Zealand and Luna Rossa Prada Pirelli. The stakes are sky-high: whoever wins the America’s Cup not only earns the historic America’s Cup ‘Auld Mug’ trophy, but they get to write the rule for 37th America’s Cup in four years, defining the yacht design, how it is sailed – and to choose the venue where it will all take place.

It is a winner-takes-all format. The America’s Cup is famously a race in which, as Queen Victoria was informed during the first contest in 1851, “there is no second.”

HOW IS THE AMERICA’S CUP WINNER DECIDED?

The challenger, Luna Rossa Prada Pirelli, will race against the defender, Emirates Team New Zealand in the 36th America’s Cup match series starting on 10 March.

There are two races each day on 12, 13 and 14 March with additional days on 15, 16 and 17 March if needed to conclude the first-to-seven wins series.

A choice of race course is decided each day depending on wind conditions, but the courses are all windward-leewards with around 3km between each end and around 1.5km from side to side.

WHAT ARE THE DIFFERENCES BETWEEN THE TEAMS RACING FOR THE AMERICA’S CUP?

Emirates Team New Zealand, yacht Te Rehutai – The home team is the defender, having won the Cup in Bermuda in 2017. Heading it up is the steely Grant Dalton, with eight times America’s Cup campaigner Kevin Shoebridge capably in charge of the sailing side. The design team is also second to none – and between them they all set the rules this time.

The Kiwis boast some of the youngest sailors, who grew up in the era of foiling, notably the wildly gifted Pete Burling as helmsman and his Olympic champion crewmate Blair Tuke, who share a Gold and Silver Medal and six World Championship wins in the high performance 49er class.

The pair works in partnership with the team’s resident Australian Olympian, Glenn Ashby. This successful triumvirate was a crucial ingredient in Emirates Team New Zealand’s last Cup win. Ashby is key to tactical decisions, Blair Tuke is the so-called flight controller in charge of flaps on the foils and rudder, with Peter Burling is steering and coolly making those split-second decisions on the race course.

Their yacht Te Rehutai has many visible differences compared with Luna Rossa. It is a more brutal looking design beside the smooth shaped, elegant Italian boat, and has quite different shaped foils (see ‘How do the America’s Cup yacht work?’): New Zealand’s are almost flat across the wing base, while Luna Rossa’s foils are in a dihedral shape, sloping downwards from a central wing bulb.

These are just the most obvious differences, and there will be many more variations beneath the surface, especially in the complex control systems. Yet despite dissimilarities, the speed differential between teams in the Prada Cup varied only by fractions of a knot, putting the emphasis on dominating pre-start manoeuvres, reading the wind shifts and match racing the opponent. These will all play a part in the Cup match too.

Luna Rossa Prada Pirelli, yacht Luna Rossa - The Italian team, backed by Patrizio Bertelli, is bristling with experience. Italian team boss Max Sirena has been involved in six America’s Cups.

At the wheel, the Italians have a set-up never seen before, with straight-talking Australian Jimmy Spithill helming on starboard and Italian Olympic sailor Francesco Bruni helming on port. When one is steering, the other acts as flight controller and trims the foils.

It is a formidable partnership. Spithill is the most successful Cup sailor in the line-up, having been part of seven campaigns and winning it twice in 2010 and 2013 for Larry Ellison’s US team Oracle. Bruni, meanwhile, has three Olympics behind him and several Cup campaigns himself.

While this unconventional division of control between the two helmsmen prompted observers to shake their heads at first, it has proved highly successful. Spithill has suggested that the arrangement allowed them both to accelerate their skills, while at a very practical level it means no one has to jump out of the cockpit and cross the boat during high-speed G-force tacks and gybes before settling back into continuity in a new position.

Indeed, it has been so successful that Emirates Team New Zealand have been experimenting with changing to the one-helmsman-per-side arrangement, split between Peter Burling and Glenn Ashby. Watch out, this may come into play at some point.

Meanwhile, they have increasingly brought into play the tactical skills of Pietro Sibello, an Olympic 49er sailor, who is to be seen popping up to read the wind and the race course and feed back into the strategy.

HOW TO WATCH THE AMERICA’S CUP

America’s Cup racing is split into two parts throughout February and March and you can watch them all free. All the racing will be streamed live on the official America’s Cup YouTube Channel , Facebook and on americascup.com .

It will also be on free-to-air and pay-to-view networks in 120 territories around the world, including TVNZ in New Zealand, RAI and Sky Italia in Italy, the BBC and Sky UK & Ireland in the UK, and NBC Sports in the USA and Caribbean.

FIVE THINGS TO WATCH OUT FOR IN THE AMERICA’S CUP RACES

1. The pre-starts. This America’s Cup has traditional upwind starts. Each team must enter the start box from opposite ends at the two minute mark. They jostle for the best position with the aim of hitting the line powered up exactly as the clock counts down to 0:00 – and in front of their opponent.

To get an advantage, each team will look to dodge, weave, box out their opponent, put a penalty put on them, or execute some other perfectly legitimate but edge-of-the-seat manoeuvre. These minutes can be among the most exciting of a whole race, and may set the tactics and playbook for all that follows so are not to be missed.

2. Mark roundings. Teams can round either one of two marks at the top or bottom of the course, so watch for splits here, close overlaps and other tactical manoeuvres. As the boats bear away at the upwind mark rounding they head into a power zone, speeding up rapidly. This is where we have seen the AC75s exceed 50 knots of speed and get unstable and into trouble with flight control.

3. Light winds. The AC75s have sometimes struggled to foil in winds of under 8 knots. When they come off their foils they suddenly go from supersonic to super-slow. Comparatively huge distances can open up or disappear in a flash if one team finds a puff and gets flying while the other is floundering. On light days, everything can turn inside out in seconds.

4. Strong winds. The same is true in big winds. Mistakes in crewing and sailhandling can be punishing when these massively loaded boats are fully powered up. When the winds are up, the pre-starts and mark roundings are likely war zones.

5. Match race tactics. Some thought the equivalent of hand-to-hand combat could never happen in the AC75s, but they have turned out to be agile and the crews surprisingly willing to throw them into some very close quarter spots. They are also able to mark opponents tack for tack and gybe for gybe round the course to defend a lead and deny their opponent a passing lane. Watch for these clever displays of aggression and stealth. And do listen in the live audio feed from each of the boats that gives big clues as to what each skipper and tactician is doing, thinking and planning.

WHAT ARE THE AMERICA’S CUP YACHTS?

Teams are racing in the AC75 design, a radical 75ft long monohull with no keel that flies on foils at speeds of up to 50 knots.

Deciding the boat to be raced is one of the spoils of victory, and when Emirates Team New Zealand won the last America’s Cup in Bermuda in 2017 they decided to create something never seen before, and where their knowledge of foiling could be a winning advantage.

The AC75 design rule is a so-called ‘box’ rule, which sets some key parameters such as hull length and overall length with bowsprit (75ft, hence the name AC75). The 62-page rule specification defines draught, minimum hull volume, number of sails, number of foils, even the number of boats – the teams have been allowed to build two and will all be racing with iteration No. 2 – but leaves other areas such as hull shape and foil flaps open for teams to develop.

As these yachts do not have keels, they rely for stability on a mere three tonnes of total ballast, plus 960-990kg allowed for 11 crew. The ballast is spread across two swivelling foils that look like arms (some say insect legs) on each side.

To keep some design costs down, the teams have one-design elements, such as the components and arms that move the foils up and down. However, the shape of the foils, the flaps and the control systems that operate them are absolutely key, and unique to each team.

The rule has also kept hull shape relatively open so we see quite striking differences in shapes. This reflects different teams’ thinking about the best way to promote foiling as early as possible in the wind range and slip as smoothly as possible between displacement and flying modes.

The sails are unique, too. The mainsails are twin-skinned soft wings, a new hybrid between a conventional sail and hard wing.

HOW DO THE AMERICA’S CUP YACHTS WORK?

The AC75s are designed to be able to fly in as little wind as possible, and as consistently as possible across the wind range up to the maximum of 23 knots allowable for the America’s Cup match.

To do that, the yachts have a canting T-foil on each side that provides the lift to take the hull out of the water and fly.

The foils are ballasted to provide stability, and are set across a large beam, so the AC75s have a huge amount of righting moment. That means they can carry a very large and efficient sail area to drive the boat.

Once the leeward foil lifts the hull clear of the water, there is very little drag, with only one slender foil and the T-foil rudder in the water. That, in a nutshell, is how it is possible for these yachts to reach 50 knots of boat speed, and potentially more.

In the real world, there are lots of variables that will affect foiling. New Zealand’s Hauraki Gulf sees a large wind range, often blustery conditions, and there are also waves to contend with. Keeping a large boat foiling efficiently and consistently on just two slender points is like juggling on a slackline, and the control systems for rapid adjustments will be a critical but largely invisible factor.

WHAT’S THE HISTORY OF THE AMERICA’S CUP?

Books could, and have, been written about the contentious history of the America’s Cup. It all began in 1851, when a syndicate of businessmen from New York sailed the schooner America across the Atlantic and beat a fleet of British yachts in a race around the Isle of Wight, winning the 100 Guinea Cup.

Famously, Queen Victoria, who had watching the race, asked who was second and the reply came: “Your Majesty, there is no second.”

The 100 Guinea Cup was donated to the New York Yacht Club, renamed in honour of the schooner and a Deed of Gift drawn up for ‘a perpetual challenge cup for friendly competition between nations’. The America’s Cup is the oldest trophy in international sport and arguably the most difficult (and expensive) to win.

For 160 years, Britain has been trying to win it back. Challengers have included the tea magnate Sir Thomas Lipton, who challenged five times between 1899 and 1930.

After a golden era of racing in the J Class yachts, the Cup was raced for in the 12-metre design, then an evolving International America’s Cup Class. More recently it has been contested in much faster multihull designs.

The America’s Cup has always been defined by, and contested with, the backing of some of the world’s wealthiest businessmen. Winners have included Harold Vanderbilt (1930, 1934 and 1937) and Henry Sears (1958).

In the modern era, Ernesto Bertarelli’s team Alinghi won in 2003 and 2007 before losing to Larry Ellison’s Oracle Racing in 2010. Ellison’s US team successfully defended in 2013 before losing to New Zealand in 2017.

Both men retreated from the America’s Cup following their defeats, but Patrizio Bertelli, CEO of the Prada Group, is still trying to win it for Italy after five Cup campaigns with the Luna Rossa Challenge.

Since 1851, the US has defended or won the America’s Cup 30 times, New Zealand three times, Switzerland (Alinghi) twice, and Australia once (Alan Bond’s Australia II in 1983). Despite 16 challenges in a Cup match since 1870, Britain has never yet won back the trophy that left its shores in 1851.

WHAT IS THE AMERICA’S CUP TROPHY?

The America’s Cup , affectionately known as the ‘Auld Mug’ is an impressive piece of silverware. Including its pedestal, it stands 1.1m high and weighs over 14kg. It was made by London-based silver maker Robert Garrard & Co, the royal jeweller since 1735, and was originally a claret jug.

It was given an extra pedestal in 1958 to make room for more engraving, and when that ran out of space, another was added in 1992.

A little known fact (which says so much about America’s Cup rivalry) is that when Oracle won the trophy in 2010 the engraving marking rivals Alinghi’s victory was rotated round to the rear. A new base in carbon fibre was also made to replace the mahogany one.

When Louis Vuitton sponsored the challenger series, the America’s Cup was given its own large Vuitton trunk on its 150th birthday in 1998. With Oracle as the holder it was accompanied everywhere and closely guarded by white-gloved bodyguards.

On winning it in 2017, Emirates Team New Zealand took it to yacht clubs round its home country and let members and young sailors handle the famous silver trophy.

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