catamaran speed calculator

Catamaran Hull Speed Calculator For Beginners (Table and Free Spreadsheet)

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Speed is important, it can get you out of harm’s way, and it makes sailing much more fun, but figuring out how fast a catamaran will be able to sail can be tricky. One important aspect is to understand maximum hull speed.

In this article, I have calculated different hull speeds for different lengths of boats; this includes both monohulls and catamarans but focuses on the latter. Here is the catamaran maximum hull speed table:

Table of Contents

Catamaran Max Hull Speed Calculator Table

Table explanation.

Length on the waterline (L.W.L.): Length of the boat when measured on the waterline, not to be confused with length overall (L.O.A.), which is the boat’s total length (above the waterline) including bowsprit, etc.
Displacement max hull speed: The max speed of a boat whose L.W.L doesn’t change when underway and where the vessel’s bow wave is the limiting speed factor.
Semi/Light Displacement or Semi planing hulls speed: A boat where the bow waves speed limiting factors can be partially overcome and therefore exceed the displacement hull speed. These hulls usually overcome hull speed by 10-30% .

How to use the Catamaran Hulls Speed Table

Choose your length on waterline in the left-most column, either in feet or meter.
Continue reading to your right and stop either at “Displacement hulls speed” or continue to “10,20, or 30%”, depending on your estimated hull efficiency. This will be your calculated maximum hull speed for a semi-displacement catamaran.

The Formula

First of all, we need to know the maximum hull speed for a displacement hull, and from that number, we will be able to calculate how much faster the semi-planing (or semi-displacement) hull will be. This is the formula for Maximum Hull Speed on a displacement boat:

Now we need to add the increased efficiency (loss of drag) of a semi-displacement hull, usually, this is somewhere between a 10-30% increase.

Note: “1.3” is the increase in efficiency, if you believe you are on the lower end of the scale this would be 1.2 or 1.1.

How to Exceed Hull Speed

This calculator offers a theoretical perspective, but many other factors such as sail plan, weight, and sailor skill, of course, have a profound impact on speed. As we have seen, a semi-displacement hull can exceed maximum hull speed, but we can also see that it isn’t by much. The next step is to reduce drag even further by utilizing a planning hull.

Catamaran Hull Speed Spreadsheet

If you want more info, calculate other lengths, or see the speeds in Km/h or Mph then I suggest you check out this free spreadsheet.

Catamaran Freedom Hull Speed Calculator

Note: If you want your own copy just click, File->make a copy.

Common Questions About Catamaran Hull Design

Below I will answer some of the questions I receive concerning catamaran hull design. The list will be updated as relevant questions come in.

Is a Catamaran a Planing hull?

As we have discussed above, a catamaran can definitely have a semi-planing hull, but can it be designed in a fully planing configuration as well?

Catamarans can be configured as planing hulls, although most sailing catamarans are set up as either semi-planing or hydrofoil. Due to the high speeds needed to get a boat to planing speed, this is only possible on racing sailboats or motor-powered catamarans such as high-speed ferries.

Owner of CatamaranFreedom.com. A minimalist that has lived in a caravan in Sweden, 35ft Monohull in the Bahamas, and right now in his self-built Van. He just started the next adventure, to circumnavigate the world on a Catamaran!

Hull Speed Calculator

About hull speed calculator (formula).

A Hull Speed Calculator is a tool used in naval architecture and boating to estimate the maximum speed at which a displacement hull (typically found in sailboats and some smaller powerboats) can move through the water without planing. This calculation is based on the hull’s length at the waterline (LWL). The formula for calculating the hull speed is as follows:

Hull Speed (HS) = 1.34 x √(LWL)

Hull Speed (HS) is the estimated maximum speed of the boat in knots (nautical miles per hour).
LWL is the length of the waterline of the boat, typically measured in feet or meters.

The factor 1.34 in the formula is an approximation, and it is derived from the constant 1.34 (or 1.5 in some sources) times the square root of the waterline length. The Hull Speed represents the theoretical maximum speed a displacement hull can reach without climbing up onto the water’s surface and transitioning into planing mode.

Hull Speed Calculators are valuable tools for boat designers, builders, and sailors as they help determine a boat’s potential speed based on its hull characteristics. Knowing the hull speed is essential for safe and efficient navigation, as exceeding this speed can lead to increased drag, reduced fuel efficiency, and potential safety risks in adverse conditions.

Catamaran Design Formulas

Post author By Rick
Post date June 29, 2010
10 Comments on Catamaran Design Formulas

Part 2: W ith permission from Terho Halme – Naval Architect

While Part 1 showcased design comments from Richard Woods , this second webpage on catamaran design is from a paper on “How to dimension a sailing catamaran”, written by the Finnish boat designer, Terho Halme. I found his paper easy to follow and all the Catamaran hull design equations were in one place. Terho was kind enough to grant permission to reproduce his work here.

Below are basic equations and parameters of catamaran design, courtesy of Terho Halme. There are also a few references from ISO boat standards. The first step of catamaran design is to decide the length of the boat and her purpose. Then we’ll try to optimize other dimensions, to give her decent performance. All dimensions on this page are metric, linear dimensions are in meters (m), areas are in square meters (m2), displacement volumes in cubic meters (m3), masses (displacement, weight) are in kilograms (kg), forces in Newton’s (N), powers in kilowatts (kW) and speeds in knots.

Please see our catamarans for sale by owner page if you are looking for great deals on affordable catamarans sold directly by their owners.

Length, Draft and Beam

There are two major dimensions of a boat hull: The length of the hull L H and length of waterline L WL . The following consist of arbitrary values to illustrate a calculated example.

L H = 12.20 L WL = 12.00

After deciding how big a boat we want we next enter the length/beam ratio of each hull, L BR . Heavy boats have low value and light racers high value. L BR below “8” leads to increased wave making and this should be avoided. Lower values increase loading capacity. Normal L BR for a cruiser is somewhere between 9 and 12. L BR has a definitive effect on boat displacement estimate.

Tags Buying Advice , Catamaran Designers

Owner of a Catalac 8M and Catamaransite webmaster.

10 replies on “Catamaran Design Formulas”

Im working though these formuals to help in the conversion of a cat from diesel to electric. Range, Speed, effect of extra weight on the boat….. Im having a bit of trouble with the B_TR. First off what is it? You don’t call it out as to what it is anywhere that i could find. Second its listed as B TR = B WL / T c but then directly after that you have T c = B WL / B TR. these two equasion are circular….

Yes, I noted the same thing. I guess that TR means resistance.

I am new here and very intetested to continue the discussion! I believe that TR had to be looked at as in Btr (small letter = underscore). B = beam, t= draft and r (I believe) = ratio! As in Lbr, here it is Btr = Beam to draft ratio! This goes along with the further elaboration on the subject! Let me know if I am wrong! Regards PETER

I posted the author’s contact info. You have to contact him as he’s not going to answer here. – Rick

Thank you these formulas as I am planning a catamaran hull/ house boat. The planned length will be about thirty six ft. In length. This will help me in this new venture.

You have to ask the author. His link was above. https://www.facebook.com/terho.halme

I understood everything, accept nothing makes sense from Cm=Am/Tc*Bwl. Almost all equations from here on after is basically the answer to the dividend being divided into itself, which gives a constant answer of “1”. What am I missing? I contacted the original author on Facebook, but due to Facebook regulations, he’s bound never to receive it.

Hi Brian, B WL is the maximum hull breadth at the waterline and Tc is the maximum draft.

The equation B TW = B WL/Tc can be rearranged by multiplying both sides of the equation by Tc:

B TW * Tc = Tc * B WL / Tc

On the right hand side the Tc on the top is divided by the Tc on the bottom so the equal 1 and can both be crossed out.

Then divide both sides by B TW:

Cross out that B TW when it is on the top and the bottom and you get the new equation:

Tc = B WL/ B TW

Thank you all for this very useful article

Parfait j aimerais participer à une formation en ligne (perfect I would like to participate in an online training)

‍ Catamaran Speed by Type

Catamaran design can be split into different categories. After all, different vessels are designed for different tasks, as speed isn’t always the most important design consideration.

The fastest type of catamaran is the ultralight racing catamaran. These vessels have extremely narrow hulls and a remarkable planing ability. They’re designed to pierce waves and often achieve speeds in excess of 45 knots or greater, depending on conditions.

The second fastest catamaran variety is the sport catamaran. Sport catamarans often include a fairly good level of creature comforts in the cabin. They’re technically hybrid designs, because they are envisioned as a combination between a racer and a cruiser. Sport catamarans can achieve 30 knots or greater.

Cruising catamarans are designed primarily for safety and comfort. They’re often used for long offshore passages, where speed is important, but comfort is king. Despite their accommodations, cruising catamarans can still achieve a respectable 15 to 20 knots of speed—sometimes 50% faster than similarly-equipped monohulls.

Why are Catamarans So Fast?

Catamarans are remarkable vessels that can achieve amazing speeds. As a result of their unconventional design, typical calculations for hull speed (such as those used for monohulls) don’t always apply.

But what makes catamarans so much faster than equivalent monohulls? The first and most obvious speedy design element are the hulls themselves.

Catamarans don’t have a deep keel or a centerboard. This is because the second hull acts as a stabilizing device, and it helps the vessel track straight. The lack of a keel reduces weight (and equally important). It also reduces drag.

Additionally, catamarans behave in strange ways while underway. The hulls have a tendency to rise out of the water further the faster they go. This further reduces drag and makes it easier for the vessel’s speed to climb once it starts to move.

One additional characteristic is how the vessel’s sails point relative to the wind. Catamarans keep their sails perpendicular to the wind, which allows them to harness energy more efficiently. This is because, at a perpendicular angle, less wind energy is lost by spillage over the edge of the sails.

Are Catamarans Faster than Monohulls?

Yes, catamarans are typically faster than monohulls. They’re also a lot more stable, as their spaced-out hulls provide better motion comfort in rough seas. Catamaran hulls are narrower than monohulls, which also reduces drag and increases speed.

Catamaran vs. Monohull Speeds

We know that catamarans are faster than monohulls in most situations. But how much faster are they? Here’s a table of hull speeds for monohulls, which is a useful reference when comparing speed. Hull speed isn’t the absolute fastest that a boat can go, but it’s a good practical estimate for understanding the hydrodynamic limitations of single-hull designs.

Hull speed calculations for catamarans are more complicated. This is because catamarans have a greater length-to-beam ratio. And due to their narrow hulls and open center, they aren’t affected by the same hydrodynamic drag forces that monohulls are limited by.

For example, a 55-foot monohull sailboat with a waterline length has a hull speed of 9.4 knots or 10.9 mph. Its actual speed could exceed that in the right conditions, but rarely by more than a few knots.

Compare that to an efficient 51-foot catamaran, which can easily achieve speeds in excess of 20 knots in reasonable winds. That’s more than double the hull speed of a monohull with a similar waterline length and proves that catamarans operate under a completely different set of rules.

Wave Piercing

One aspect of catamaran design that makes them superior speeders is their ability to pierce waves. Specially designed catamarans have minimal buoyancy at the bow, which allows them to slice through waves instead of going over them.

This increases the speed at which catamarans can cover the distance. Think about it—a boat going over a wave has to use more energy to reach the same destination, as the height of the wave almost makes the distance further.

It’s like walking over a hill or on flat ground—you’ll take more steps walking up and down the hill than in a straight flat line. Wave piercing catamarans enjoy better stability, and they ‘take the flat road’ to a greater extent than monohulls.

Do Catamarans Plane?

Planing is when a boat’s hull rises out of the water due to hydrodynamic lift. This increases speed and efficiency, as there’s less drag but sufficient contact for stability. It also reduces rolling, as the bow only contacts the taller portions of the waves.

Catamarans have planing characteristics, but they generally don’t plane as dramatically as powerboats. This is still worth noting, as catamarans are specifically designed to use the phenomenon of hydrodynamic lift to gain speed and efficiency.

You’ll visibly notice a catamaran’s hull rising out of the water as it increases in speed. Compare that to a displacement monohull design (such as a classical cruising sailboat with a deep keel), which won’t rise out of the water in any significant way.

Are Catamarans Faster than Trimarans?

A trimaran is a catamaran with an additional hull in the center. Trimarans are usually less common than catamarans, but they have some of the same design benefits as other multi-hull sailboats.

At first glance, it would seem logical that trimarans are slower than catamarans. After all, they have an extra hull in the center, which likely increases weight and drag. However, there are more important factors at play here.

Trimarans are almost universally faster than catamarans. This has to do with weight distribution. Trimarans center their weight over the middle hull, using the outer hulls primarily for stability. This allows them to reap the benefits of a catamaran while increasing the efficiency of the wind power it captures.

Fastest Catamarans

Catamarans are popular for racing. There are several world records held by catamarans and numerous production boats with especially impressive speed-to-size ratios. Here are a few of the fastest racing and production catamarans ever built.

Fastest Sailboat Ever—Vestas Sailrocket 2

The Vestas Sailrocket is a specialized racing boat designed only for speed. This incredible vessel is actually the fastest sailboat ever built—and no wonder it’s a catamaran. A monohull simply can’t achieve record-breaking speeds when put head-to-head with a lightweight multi-hull.

The vessel, which earned the world sailboat speed record in 2012, has a modest 150 to 235 square feet of sail. Nonetheless, it managed to achieve a remarkable top speed of 65.45 knots in only 25 knots of wind. That’s about 72 miles per hour—in a sailboat.

Soon, a team of Swiss engineers will release their own version designed to beat the 65-knot speed record. Their vessel, which is a hydrofoil, will attempt to hit an incredible target speed of about 80 knots.

Outremer Catamarans

But what about production catamarans? How do they stack up, and how fast can they go? French boat builder Outremer Catamarans builds some of the fastest production catamarans ever built. These are not specialty racing boats—in fact, they’re average-sized cruising catamarans.

Let’s use the larger Outremer 51 as an example. This high-end cruising cat is known for its almost outrageous speed capabilities. In ideal conditions, owners of the Outremer 51 have reported speeds exceeding 20 knots for extended periods.

That’s a production catamaran with speeds that rival 20th-century warships. With such a fast boat, the world’s oceans start to appear a lot smaller. Plus, the genius design of the Outremer 51 allows it to be crewed by just two people.

But how do Outremer catamarans achieve such high speeds? The secret is in precise engineering and hull design, along with a sail plan that’s perfectly catered to the vessel. The hulls are sleek and narrow and designed to cut through the water with minimal drag.

From the bow, the Outremer 51 hulls look paper-thin. They increase in width gradually, which eliminates areas of sudden drag. These narrow hulls evenly distribute the vessel’s 21,825-lb displacement. Its low-buoyancy bows reduce drag and blast through waves instead of riding over them.

I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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Hull Speed Calculator for Marine Engineering

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Hull speed is a crucial concept in marine engineering, which refers to the theoretical maximum speed that a displacement hull can achieve efficiently. The concept is based on the length of the waterline, and the speed is calculated using a specific formula. This article discusses the Hull Speed calculation, its origin, applications, and significance in marine engineering and naval architecture.

Example Formula

The Hull Speed (V h ) of a boat can be calculated using the following formula:

V h : Hull Speed in knots
L wl : Length of the waterline in feet

Impact on Society

The Hull Speed concept has played a significant role in the design and construction of ships and boats. It has helped marine engineers and naval architects to design hulls that are more efficient and economical. Understanding hull speed is crucial for optimizing fuel consumption and achieving efficient voyage planning. Additionally, this concept is essential in various sports, such as sailing, where knowing the hull speed can help in maximizing performance.

Real Life Application in Industry

Hull speed is widely used in the marine industry, especially in shipbuilding. For example, in the design phase of a cargo ship, engineers need to calculate the hull speed to determine the most efficient hull shape and length. This calculation ensures that the ship can carry the maximum amount of cargo while using the least amount of fuel, thus maximizing profits. Furthermore, in sailing races, skippers use the concept of hull speed to estimate the maximum efficient speed they can achieve, which is critical for race strategies.

Key Individuals in the Discipline

William Froude (1810-1879) was an English engineer and naval architect who is known for his work in ship hydrodynamics. He introduced the concept of hull speed and the Froude number. His work on the resistance of ships and the efficiency of hulls remains a foundation in marine engineering and naval architecture.

Interesting Facts

The concept of hull speed is fundamental in naval architecture and marine engineering, but it's also used in paddlesports like kayaking and canoeing to estimate the maximum efficient speed.
Hull speed is sometimes referred to as the "displacement speed" because it is most relevant when the hull is moving through the water, displacing its volume.
Advanced materials and hull designs have allowed modern ships and boats to exceed their theoretical hull speed without excessive power requirements.

Understanding hull speed is essential for marine engineers and naval architects. It is a fundamental concept that plays a significant role in ship design and construction. The hull speed is not just theoreticalbut has practical applications in optimizing fuel consumption, load-carrying capacity, and overall efficiency of a ship. Innovations in materials and hull designs continue to challenge and extend the traditional concepts of hull speed, but the foundational understanding remains pivotal for aspiring marine engineers and naval architects.

A comprehensive tutorial on hull speed, its calculation, applications, and importance in marine engineering

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Hull Speed Calculator

Author: Calculator Academy Team

Last Updated: July 28, 2023

Enter the waterline of the boat in feet while under motion into the calculator to determine the hull speed.

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Hull Speed Formula

The following formula is used to calculate a hull speed:

Where HS is the hull speed (MPH)
WL is the water line (ft)

This formula is only an estimate. The true speed depends on the weight and shape of a hull as well.

What is hull speed?

Definition:

Hull speed is a measure of the velocity of a sea fairing vessel with respect to its hull.

The hull speed is a factor of the waterline measured on the hull speed when the boat is traveling.

How to calculate hull speed?

The following example problem outlines the steps required to calculate the hull speed of a boat.

First, determine the waterline when the boat is under motion. In this example, the water line is measured to be 10 FT.

Next, the final and last step is to simply plug the waterline value into the formula above to calculate the hull speed:

HS = 1.35 * SQRT (WL)

HS = 1.35 * SQRT (10)

HS = 4.2609 MPH

Boat Speed Calculator

Table of contents

The boat speed calculator determines the top speed of a boat based on the boat's power and displacement . If you wonder how fast a boat can go, this calculator will help you answer that. The calculator also utilizes a constant known as Crouch constant which differs based on the type of the boat.

The formula for the top speed of a boat is used by designers to perform preliminary design analysis of the hulls. This helps in keeping the cost of building a boat in check (visit the boat loan calculator for more). Read on to understand how to calculate the speed of your yacht using Crouch's formula and to know how much horsepower do I need for my boat?

What is boat speed — Calculating using Crouch's formula?

The speed of the boat, in simple words, is how fast it can go. However, unlike land vehicles, this speed is not a ratio of distance and time. The speed of a boat having an engine to deliver P horsepower and displacing D pounds is written as:

where S is the boat speed and C is the Crouch constant. The above equation is known as Crouch's formula.

Note: The formulation and value for the Crouch constant are specific for units such as the speed in miles per hour and displacement in pounds.

💡 Our tools can convert units automatically, but if you'd like to learn how to do these conversions yourself, then our speed conversion and torque to hp calculator could come in handy!

What is displacement?

The displacement for a boat is defined as the volume of water displaced . The volume is then converted to weight. This property of a ship is an application of Archimedes' principle . In other words, the displacement of a boat is its weight. This weight is usually measured in tonnes or pounds. For instance, a modern US Navy Gerald R. Ford-class aircraft carrier displaces about 100,000 tons at its full load, whereas a 17th-century fishing boat displaces only about 13 tons. The tonnage of the ship varies as per its class and purpose.

Keep reading about Archimedes' principle at our Archimedes' principle calculator and find out if an object sinks or floats in a liquid!

Crouch constant

The Crouch constant depends on the type of boat . The constant is applicable to a wide variety of boats, from runabouts to high-speed racing boats. It does not take the hull length into account. The table below has the value of the Crouch constant for different types.

How to calculate boat speed using this calculator?

Follow the steps below to calculate boat speed:

Step 1: Enter the shaft horsepower value, P .

Step 2: Insert the boat's displacement , D .

Step 3: Choose the Crouch constant , C from the list of boat types , or you can directly enter the value.

Step 4: The boat speed calculator will now return the value of boat's top speed.

Example of using the boat speed calculator

Calculate the speed of a racing hydroplane having an engine that delivers 3000 hp and displaces 6800 pounds of water.

To calculate boat speed :

Step 1: Enter shaft horsepower value P = 3000 hp .

Step 2: Insert the boat's displacement , D = 6800 lbs .

Step 3: Choose the Crouch constant , C from the list for hydroplanes, i.e., C = 220 .

Step 4: Using the Crouch's formula: S = √(P / D) × C = √(3000 / 6800) × 220 = 146.13 mph i.e., the speed of the hydroplane is about 146.13 miles per hour.

Alternatively, you can also run this calculator backward to know how much horsepower I need for my boat to achieve a certain speed. Say you want a top speed of 150 miles per hour for your 6,000 lb hydroplane. You can then:

Step 1: Enter top speed value S = 150 mph .

Step 2: Insert the boat's displacement , D = 6000 lbs .

Step 4: The calculator will use Crouch's formula to return the horsepower value as: Power = (P / C)² × D = (150 / 220)² × 6000 = 2789 hp

Therefore, you need an engine to deliver about 2800 hp to take your boat as fast as 150 mph .

How do I calculate a boat's top speed?

To calculate the boat speed:

Divide the power delivered by the boat to the displacement.

Find the square root of the result from step 1.

Multiply by the Crouch constant.

S = √(P / D) × C

What is Crouch's formula?

Crouch's formula is the equation to find the top speed of a boat based on its power P and tonnage D . The speed of the boat, S is given by the equation.

What is the value of Crouch's constant for a racing boat?

A racing boat has the value of Crouch constant around 210 .

What is the value of Crouch's constant for runabout boats?

An average runabout has the value of Crouch constant around 150 whereas it can go up to 190 for high-speed runabouts .

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Quantum physicist's take on boiling the perfect egg. Includes times for quarter and half-boiled eggs.

You can use this price per pound calculator to find the price of an item or items per pound.

Shaft horsepower (P)

Boat displacement (D)

Crouch's constant (C)

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Boat Speed Predictions

Please note - by using this calculator you agree to the following license provisions: This calculator is for non-commercial use by the general public only. It is proved for entertainment only and not intended to be used for any other purpose. Commercial use for any reason is prohibited. A license for commercial use may be available upon application to BAM Marine on a per use or annual basis.

There are so many factors that affect boat speed that it is hard to make accurate estimates of what the real top end will be. Mercury Marine uses the following formula to estimate potential top end, this calculator uses this formula.

The Square Root of (Total Shaft Horsepower / Weight ) x Constant = Speed

The constants have been developed from experience, and are as follows:

The constants above are from close to 20 years ago. There have been so many changes in hull design that today they are not even close. To be honest our business has changed and we have not done enough recent testting to update them. The best thing to do is calculate a constant from published tests or your personal setup and go from there.

The calculator below uses the above formula. Plug in your info, and click "Calculate" on the item you want to compute. By using known values for the weight, power and speed you can come up with a more accurate constant for your boat. You can then see what effect changes to weight or power will have on top speed. Using the calculator in this fashion will produce surprisingly accurate results.

Boat Speed Calculator

Planing Boat Speed Calculator

Planing boat speeds vary based on factors like size and design. Smaller boats around 12 feet may plane at 8-10 knots (9-12 mph), while larger 40-foot boats can plane at 35-45 knots (40-52 mph). These estimates are approximate and subject to variation due to hull shape, weight, and engine power.

How do you calculate the planing speed of a boat? Planing speed depends on factors like boat size, weight, and hull design. It generally starts around 15-20 knots (17-23 mph) for smaller boats and can go higher for larger vessels.

What is the speed of the hull of a planing boat? The speed of the hull of a planing boat is roughly equal to its planing speed, which can vary as mentioned earlier.

What is the crouch’s formula for planing speed? Crouch’s formula is a guideline for estimating planing speed and is expressed as: Planing Speed (in knots) ≈ √(Length at Waterline in feet).

How fast can a 30hp boat go? A 30hp boat can typically reach speeds of 20-30 mph (17-26 knots) depending on its size, weight, and hull design.

What speed should a semi-planing hull be? Semi-planing hulls usually start planing around 10-15 knots (12-17 mph).

Is 35 mph fast for a boat? Yes, 35 mph is considered a fast speed for a boat, especially for smaller recreational vessels.

Are planing hulls faster? Planing hulls are generally faster than displacement hulls once they get on plane.

What is the best planing hull for rough water? Deep-V hulls are often considered the best for rough water conditions due to their ability to cut through waves.

What are the disadvantages of a planing hull? Disadvantages of planing hulls include reduced fuel efficiency at high speeds, less stability at lower speeds, and a tendency to pound in rough seas.

How do you calculate critical rpm? Critical rpm is specific to an engine and not related to boat speed. It’s the engine’s maximum safe RPM, typically specified by the manufacturer.

How do you calculate surface speed? Surface speed depends on boat speed and water conditions. It’s usually close to the speed of the boat on plane.

How do you calculate speed triangle? The “speed triangle” is not a standard term in boat navigation or design. It’s possible you’re referring to the relationship between boat speed, engine power, and hull design, which is complex and not typically represented as a triangle.

Is 500 hours on a boat engine a lot? 500 hours on a boat engine is generally considered moderate use, but it depends on maintenance and the engine’s design.

What is the most efficient speed for a boat? The most efficient speed for a boat is often around 70-75% of its maximum hull speed, which varies based on hull design.

How fast is 170hp on a boat? A 170hp boat can reach speeds of 35-50 mph (30-43 knots) or more depending on the boat’s size and design.

Does a planing hull ride on top of the water? Yes, a planing hull rides on top of the water’s surface when it reaches planing speed.

Is planing a boat good? Planing allows boats to achieve higher speeds and smoother rides in certain conditions, making it a desirable characteristic for many boat types.

Can you exceed hull speed? Yes, it is possible to exceed hull speed with a powerful engine or specialized hull design, but it requires significantly more power and is less efficient.

Is 50 MPH fast for a boat? Yes, 50 mph is considered a fast speed for a boat, especially for recreational vessels.

How fast is 30 knots on a boat? 30 knots is approximately 34.5 mph (55.5 km/h).

What is considered a fast boat? A boat that can reach speeds of 40 mph (34.8 knots) or more is generally considered fast.

What is the most efficient hull shape? The most efficient hull shape depends on the specific application, but catamaran and trimaran hulls are known for their efficiency.

Does waxing a boat hull make it faster? Waxing a boat hull can reduce friction and improve its hydrodynamics slightly, potentially increasing speed marginally.

What is the most efficient hull form? A hull form’s efficiency depends on the purpose. For displacement boats, a long, slender hull is efficient. Planing boats benefit from V-shaped hulls.

What type of boat is best for choppy water? A deep-V hull is often the best choice for boats that will encounter choppy water as it provides a smoother ride and better handling.

Do flat bottom boats plane? Some flat-bottomed boats can plane, but they are generally not as efficient at planing as boats with V-shaped hulls.

What is the best hull design for speed? For high-speed performance, a hydroplane or stepped hull design is often used.

Which hull type would not be a good choice for rough water? A flat-bottomed hull is not a good choice for rough water due to its lack of stability in waves.

What is most likely to have a planing hull? Small powerboats, speedboats, and some fishing boats are most likely to have planing hulls.

What is the safest hull design? The safest hull design depends on the intended use. For offshore and rough water, a deep-V hull is often considered safer due to its ability to handle waves.

What is 1st and 2nd critical speed? 1st critical speed refers to the first natural frequency of vibration of a boat’s hull. The 2nd critical speed is the second such frequency.

What is first critical speed? The first critical speed is the lowest speed at which a boat’s hull resonates or vibrates due to water flow, potentially causing discomfort or damage.

What is normal RPM count? Normal RPM count for a boat engine varies widely depending on the engine type, but it typically ranges from 2,000 to 4,000 RPM.

What is the formula for speed per hour? Speed per hour is simply the boat’s speed in knots or mph.

What is speed formula number? There is no specific “speed formula number.” Speed is typically measured in knots (nautical miles per hour) or miles per hour.

How do you convert RPM to speed? The RPM-to-speed conversion depends on the boat’s gear ratio, propeller size, and hull design. It’s not a straightforward formula and requires specific data for accurate conversion.

What is the formula of speed with angle? The formula to calculate speed with an angle is not a standard concept in boating. Speed is typically measured without considering angles.

How do you find speed with height and angle? The relationship between height and angle does not directly determine speed. Speed calculations are based on distance traveled and time.

How do you find speed without time? Speed is calculated as distance divided by time, so you cannot find speed without knowing the time it took to cover that distance.

How many hours is OK on a boat? The number of hours on a boat engine depends on maintenance and usage. A well-maintained engine can last thousands of hours.

Why do boat engines not last long? Boat engines may not last as long if not properly maintained, operated at high RPMs constantly, or exposed to harsh saltwater conditions.

How far can a motor boat go in 6 hours? The distance a motor boat can go in 6 hours depends on its speed. At an average speed of 20 knots, it can cover approximately 120 nautical miles (138 miles or 222 kilometers).

Why don’t boats use MPH? Boats often use both knots (nautical miles per hour) and miles per hour (mph) for speed measurement. Knots are more common in marine navigation due to nautical conventions.

What is the best speed to polish a boat? There is no specific speed for polishing a boat; it can be done when the boat is stationary or out of the water.

Can a boat go faster than the wind? Sailboats can achieve speeds faster than the wind’s speed by using their sails efficiently.

How fast does a 900 hp boat go? A 900hp boat can reach speeds of 80-100 mph (70-87 knots) or more, depending on its size, design, and purpose.

How much horsepower does a normal speed boat need? A normal speed boat often requires 150-300hp for recreational use, but it varies based on boat size and purpose.

What is the best hull shape for waves? A deep-V hull is often the best choice for handling waves as it provides a smoother ride and improved wave penetration.

Why are boats V-shaped? Boats are often V-shaped (deep-V hulls) to improve stability, handling in rough water, and overall performance.

Why does my boat struggle to plane? Boats may struggle to plane due to excessive weight, incorrect trim, or engine/power issues.

How can I make my boat plane faster? To make a boat plane faster, reduce weight, optimize engine performance, and trim the boat correctly.

What is the planing speed of a hull? The planing speed of a hull depends on its design, size, and weight but typically starts around 15-20 knots (17-23 mph).

How much horsepower does it take to get the hull speed of a boat? To reach hull speed, a boat typically needs one horsepower for every 500 pounds of displacement. Estimating this, a 20,000-pound boat would require about 40hp.

What is critical hull speed? Critical hull speed is the maximum speed a displacement hull can reach without creating excessive drag and inefficiency. It’s approximately 1.34 times the square root of the boat’s waterline length in feet.

At what speed boats are most efficient? Boats are most efficient when operated at speeds below their planing threshold but above idle, typically around 70-75% of their maximum hull speed.

How fast is 25 knots on a boat? 25 knots is approximately 28.8 mph (46.4 km/h).

What is the best cruising speed for a boat? The best cruising speed for a boat depends on its design, but it’s typically around 70-75% of its maximum hull speed for efficiency.

How fast is 40 knots on a boat? 40 knots is approximately 46.1 mph (74.2 km/h).

How fast is 20 knots at sea? 20 knots is approximately 23.0 mph (37.0 km/h).

Is 50 mph fast for a boat? Yes, 50 mph is considered fast for a boat, especially for recreational vessels.

What is the best shape for a boat to hold the most weight? A flat-bottomed boat or a barge-style hull is best for holding the most weight, as it provides greater buoyancy.

What is the most efficient speed for a displacement hull? The most efficient speed for a displacement hull is typically just below its hull speed, around 70-75% of that speed.

Should I wax my boat twice? Waxing your boat twice, with proper preparation in between, can provide better protection and shine, but it’s not always necessary.

Does polishing a boat make it faster? Polishing a boat can reduce friction and improve hydrodynamics slightly, potentially increasing speed marginally.

What is the best hull design for choppy water? For choppy water, a deep-V hull design is often considered the best choice as it offers improved stability and handling.

Which is more stable, V hull or flat bottom? A V hull is generally more stable than a flat-bottomed hull, especially in rough water conditions.

What size waves can a boat handle? A boat’s ability to handle waves depends on its design and size. Smaller boats may handle waves up to 2-3 feet, while larger vessels can handle much larger waves.

Which type of hull is most efficient? The efficiency of a hull depends on the intended use. For displacement vessels, a long, narrow hull is efficient. Planing boats benefit from V-shaped hulls.

Why are flat bottom boats better? Flat bottom boats are better for certain applications, such as shallow water and calm conditions, because they offer stability and ease of grounding.

Why are boats not flat on the bottom? Boats are not flat on the bottom to improve their stability, reduce pounding in waves, and enhance their overall performance.

Can you exceed hull speed? It is possible to exceed hull speed with sufficient power, but doing so is less efficient and may result in excessive drag and fuel consumption.

What makes a boat hull fast? A combination of factors makes a boat hull fast, including its design, shape, weight, power, and hydrodynamics.

What is the most stable boat in rough water? A deep-V hull is often the most stable boat in rough water due to its ability to slice through waves and provide a smoother ride.

What is the best deadrise for rough water? A deadrise angle of 18-25 degrees is often considered ideal for boats designed to handle rough water.

GEG Calculators is a comprehensive online platform that offers a wide range of calculators to cater to various needs. With over 300 calculators covering finance, health, science, mathematics, and more, GEG Calculators provides users with accurate and convenient tools for everyday calculations. The website’s user-friendly interface ensures easy navigation and accessibility, making it suitable for people from all walks of life. Whether it’s financial planning, health assessments, or educational purposes, GEG Calculators has a calculator to suit every requirement. With its reliable and up-to-date calculations, GEG Calculators has become a go-to resource for individuals, professionals, and students seeking quick and precise results for their calculations.

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Hull Speed Calculator

Are you looking to understand the maximum hull speed of your boat? In this blog, we’ll dive into the concepts, and we also have a handy hull speed calculator to help you figure out your own boat’s speed.

In short, hull speed is the theoretical maximum speed a boat or ship with a displacement hull can travel, regardless of the boat’s size or engine power. Exceeding a boat’s hull speed is highly inefficient and dangerous.

So why does it matter? What causes these speed limits? How is it calculated? Read on to find answers to all of these key questions.

Key Takeaways

Hull speed is the boat's theoretical top speed based on waterline length.
Exceeding hull speed is inefficient and can be dangerous.
Checking your hull speed helps pick the proper boat, engine, and speed.
The hull speed of a boat is calculated using a formula involving the square root of the waterline length.
Doubling a boat's waterline length will only increase its hull speed by 40%.
Wave interference at speeds exceeding the hull speed causes increased drag, greater fuel consumption, and reduced stability.
Unlike traditional displacement boats, the speed of planing hull boats isn't limited by wave interference and displacement.

How to Calculate Hull Speed? The Displacement Hull Speed Formula

The calculation uses a simple formula based on the boat’s waterline length. Here is the hull speed formula:

Hull Speed (knots) = 1.34 x √Waterline Length (feet)

So, for example, a boat with a waterline length of 20 feet would have a theoretical hull speed of:

1.34 x √20 = 8.2 kn

This formula shows that hull speed increases with the square root of the waterline length. Therefore, doubling the waterline length will increase hull speed by about 40%.

Using the Hull Speed Calculator

Here is a calculator to help you determine the theoretical hull speed for a displacement hulled boat.

Simply enter the waterline length of your vessel, choose between feet and meters, and click the button to get the hull speed in knots instantly. Want to try again? Click the “Clear” button to reset all fields.

What Causes the Displacement Speed Limit?

But why does this formula hold true? What limits a vessel’s maximum speed?

The answer lies in wave interference. As a boat moves through the water , it creates a bow wave and one at the stern. When the boat begins to exceed its hull speed, these begin to interfere with each other. This interference causes the waves to become steeper, requiring tremendous amounts of energy to climb.

Essentially, the boat hits a speed “wall” where its own wave creation prevents it from accelerating. This is why huge amounts of engine power cannot push a boat past its hull speed. The physics of wave creation forms an upper limit.

Why Does Hull Speed Matter for Your Boat?

Knowing this can help you in several ways:

Operate your boat more efficiently. Exceeding hull speed wastes fuel and stresses the engine.
Avoid dangerous situations . Pushing past hull speed can reduce control and stability.
Set realistic speed expectations. Understanding hull speed helps you pick the right boat and engine size.
Improve navigation and safety. Accounting for max speed allows better trip planning.

Vessel Hull Speed Chart & Table

Explanation of the graph.

The curve on the chart shows how the speed changes as the length increases, following the formula.

Final Thoughts

Understanding your boat’s hull speed is paramount for maintaining safety, efficacy, and optimal control at sea. Our guide has provided invaluable insights on its relevance, implications, and calculation method using the waterline length. Use our calculator to determine your boat’s hull speed.

It’s not entirely about owning the longest boat or having the most powerful engine; it’s about understanding the physics of your vessel and how it interacts with water at different speeds . Remember, being a skilled mariner isn’t just about managing the boat; it’s also about knowing your boat inside and out.

The hull speed is the speed at which a boat’s waterline length equals the bow wave’s wavelength. To calculate it, you follow this ratio: Hull speed in knots = 1.34 * sqrt(LWL in feet), where LWL is the length of the boat’s waterline.

Hull speed calculation is vital because it defines how fast a boat can go under its own displacement hull without needing significant thrust or horsepower. This calculation provides an optimal speed limit for the boat.

As the boat speeds up, the wavelength increases. Once the boat travels at a speed where the bow and stern wave synchronize, further increases in speed result in higher energy consumption but not necessarily in an increase in speed. Therefore, preventing the boat from outrunning its bow wave is beneficial to maintain optimal energy use.

This refers to any ship or boat designed to displace water equal to its own weight. These vessels have a hull speed, the theoretical maximum speed they can achieve without riding on the plane.

The hull speed is the speed at which the length of the bow wave equals the waterline length of the boat. As the boat starts to move at this speed, it will take a significant increase of energy to make the boat move even slightly faster. That’s why a traditional sailboat can’t naturally move faster than the hullspeed.

The hull speed is generally considered the maximum efficient speed for a displacement boat; exceeding it requires exponentially more energy. However, powerboats, planing boats, and other specific designs can go considerably faster than their hull speeds.

When a boat reaches 1-to-2 knots over its hull speed, the wave interference effect quickly increases drag and instability. Fuel usage and stresses also rise exponentially.

Planing hulls are designed to lift up onto the water at speed, “planing” across the surface. So they do not face the same hull speed limits as heavier displacement boats. But each hullhas performance limits.

A longer waterline length only increases hull speed by the square root. So doubling the size only increases hull speed by 40%. Often it is better to pick an efficient hull design instead of just a longer boat.

Anchor in Deep Water: Tips and Techniques

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Tools and Calculators

Boat Speed Calculator

Most of us want to know our boat’s top speed but don’t know how to calculate it. And, just as likely, we don’t think we need to. GPS is a good way to figure out your boat speed with no effort. It does all the work for you with just a glance. But it’s not always going to be available, especially if there’s a service disruption or an issue with your power. Plus, what if you want to know before you get on the water? Fortunately, calculating boat speed doesn’t have to be that hard. Let’s take a look at what you need to know.

The Basics of Calculating Boat Speed

You’ll need to know a handful of factors when calculating boat speed. This is why most of us don’t like to calculate it ourselves. And why a calculator tool is so much more helpful. However, we thinking knowing the basics behind how and why the calculator works is important, too. Even if you never need to write it out by hand.

You’ll need to know your boat’s shaft horsepower as well as its displacement. You’ll also need to include Crouch’s constant which varies based on the kind of boat we’re talking about. This number is something boat designers use when designing hull types. For instance, average runabouts have a Crouch constant of 150. A racing catamaran can be up to 230. High speed runabouts will be 190.

Horsepower works out to 550 foot-pounds per second. That equals 746 watts of energy. A number of factors affect how much horsepower is ideal for your boat. It relates to size and hull shape as much as everything else does. The general rule of thumb for horsepower is that for each horsepower you need about 5 to 40 pounds of weight. Too little horsepower and you can burn your engine out far too quickly. Too much horsepower can be dangerous. In fact, every boat is required to have a maximum horsepower rating. If you swap out your outboard motor for a more powerful one you risk damaging the boat, losing control, and worse. When it comes to HP, bigger is not always better.

Displacement

Displacement refers to the volume of water your boat displaces. This is then converted to weight to, in practical terms, you can consider displacement the boat’s weight. A racing hydroplane might displace 6700 lbs, for instance.

A Speed Calculation Example

Speed = square root of (horsepower/displacement) X Crouch Constant

Let’s take a look at an example to get a better idea with a smaller boat.

Speed = square root of ( 50 hp/800 lb) X 150

Speed = 37.5 mph

In a pinch you can work this out on your own with a pen and paper. Or, more likely, the calculator on your phone. A calculator tool makes it super easy, of course. But if you’re ever in a pinch with no power handy, it’s good to know the math behind it.

Horsepower Calculations

Another big concern for many boaters deals with horsepower. Like we said earlier, you need to have the right amount of horsepower for your boat. Too little is a struggle that can burn your engine. Too much can damage the boat and lead to accidents.

Remember, when your boat was designed, it was designed with these calculations in mind. The hull and transom are meant to support only a certain amount of pressure and weight. Even a small increase in horsepower can dramatically increase the pressure on your hull. It will also increase the torque on your transom. If it goes too far beyond manufacturer recommendations you could collapse the hull entirely.

Does this mean you can never exceed the horsepower rating of your hull? Not exactly. Accommodations need to be made. You would have to reinforce the hull and transom to handle the higher horsepower. Obviously we’re into some heavy work at this point. If you’re not sure right now how to reinforce a boat hull, you may want to stay within the established limits. Another thing to consider is whether or not you have a self-draining cockpit. A new engine could throw off the balance of your boat. That could make water enter the scuppers and soak the boat.

If you need to buy a new engine you can calculate the horsepower using the same formula. That’s the beauty of any math formula, you can solve for any single number in the equation if you know the others. So, if you want to know horsepower to achieve your desired top speed, do a reverse calculation. Let’s say in this case you want your boat to hit 50 miles per hour.

Horsepower = (speed/ crouch) squared x displacement

HP = (50/150) squared x 800

In this case, with your small boat displacing 800 lbs, if you want to reach 50 miles per hour, then you need a 90 hp engine.

One thing to remember about upgrading an engine is weight. Usually, a higher horsepower engine is also going to be heavier. The change in displacement obviously changes the figures. That said, it’s not always the case. Many modern engines do a very good job of keeping weight down.

What About Hull Speed?

Another formula for calculating hull speed for a displacement hull you might see is fairly simple. This one does not require as many numbers but also doesn’t give you the most accurate answer. The formula is

1.34 x the square root of the waterline length in feet, or 2.43 x the square root of the waterline length in meters.

For example, if you had a 16 foot boat, the square root is 4. So the formula would be 1.34 X 4 = 5.46 knots.

1 knot equals about 1.15 miles per hour so you can calculate this to mph if that’s easier for you. That takes you to 6.3 miles per hour, give or take.

This is the theoretical top speed of the vessel. That said, many factors can get in your way. How much horsepower you have, propeller slip, the condition of your boat and more alter this. Even water conditions and hull cleanliness can change your top speed.

Doesn’t Waterline Length Change?

Why does this formula exist and the other formula as well? This calculation is older and not as accurate. For instance, your waterline length can actually change as your speed increases. Thus, the accuracy is very suspect. Plus, when you add power sufficient enough to overcome hull drag, this number no longer applies. That means when you’re using your motor for propulsion, our original equation is far more useful. This one here is really more something you should be aware of. You may find it when you Google boat speeds and wonder why the different formulas exist. Even boat manufacturers ignore this calculation these days. It just doesn’t apply to modern boat making in any reasonable way.

Insurance Issues

A final note you might want to consider if you’re looking to soup up your boat. Let’s say you can get a higher horsepower engine and really boost your overall speed. That can be fun if you do it safely and, of course, safety is the number one concern. But there is another issue that may make you think twice. At the very least you’ll want to research it further to make sure it’s not a problem. Insurance.

Check with your insurance company before installing a new engine, especially if it boosts the horsepower. If you go past what the manufacturer recommended, you could be in trouble. If an accident occurs your insurance company may deny a claim.

Worse, if you are in an accident with an overpowered engine, the fault could automatically become yours. You may be considered responsible or negligent for damage caused as a result. Your insurance will not cover you and the result could be lawsuits coming your way. As such, check with any state boating regulations before you commit to anything. No sense spending time and money on something you can’t or shouldn’t do.

The Bottom Line

Knowing how to calculate horsepower and boat speed is a very useful skill. Having a handy calculator is also worthwhile. This allows you to get a better idea of how long any trip will take, how much weight your vessel can carry, and more. Plus, let’s be honest, it’s kind of cool.

My grandfather first took me fishing when I was too young to actually hold up a rod on my own. As an avid camper, hiker, and nature enthusiast I'm always looking for a new adventure.

Categories : Tools and Calculators

Craig Dahlke on March 19, 2022

Great article. In the late 1970’s I drove a recitative’s 8′ hydroplane that had a 40hp Mercury. I kneeled on the floor, and it had a dead man’s throttle. It was the fastest boat I have been in. Roughly how fast could this hydroplane go? Craig

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Advantages of Catamarans and Catamaran Hull Speeds Calculation

Categories : Marine history
Tags : Marine engineering

What is a Catamaran?

Before going into the advantages of catamarans, I’d just like to define the term. Catamarans are a class of boat that has two hulls, generally equal in size. The hulls are connected by a structure of some sort. Catamaran hull speeds are very high, making them a good choice for recreational uses. Catamaran sailboats are common, but catamaran ferry designs are quickly growing in popularity due to their unique advantages.

The catamaran is a ship design with an interesting history. The twin-hull design was first observed by Europeans in India in the late 17th century, but it was actually invented by South Pacific islanders. The capabilities of catamarans were more or less ignored in the West until 1877, when an American named Nathanael Herreshoff began developing and racing catamarans. His designs were so much faster than traditional monohull designs that sailing authorities banned them from competition for nearly a century. Today, catamarans are a popular design for recreational and racing sailboats, and are being used in efficient, low-wake ferries .

Image: Flickr , Catamaran in Cozumel.

Advantages of Catamarans

Catamarans are, in general, faster than single hull boats. This is due to several factors, the most important of which is the hull shape. Displacement hulls are the most common shapes for single hull craft. A displacement hull is supported on the water entirely by buoyancy effects. This creates a hydrodynamic drag barrier, which slows the craft. Catamaran hulls can be designed as planing or displacement hulls, but they are not slowed nearly as much by the drag barrier. Catamarans reduce drag by making use of a very thin and pointed hull design.

Catamarans are also very light, which further reduces drag and displacement. Catamarans save on weight because the multihull design eliminates the need for a keel counterweight, as the same purpose (righting the ship) is served by the hull spacing. This can make them difficult to turn, however.

Catamarans are also more stable than monohull ships, enabling designers to use more sail per foot of the boat. Stability comes from the wide beam legth; beam length is the distance from one side of the boat to the other. This wide beam and stability also allows catamarans to gain more power from heavy gusts, because they do not tend to heel over like monohulls do.

Catamaran Hull Speed

More efficient single hull boats are designed to travel with a low Froude number, which reduces but does not eliminate the drag barrier. This drag limits hull speed based on a relation involving length at waterline, given by the formula V=(gL/(2pi))1/2, where g is the gravitational constant and L is the waterline length. This is the theoretical limit for single hull displacement craft. Note that ships can sometimes exceed this theoretical limit, but to do so requires a very large power source.

The calculations for a catamaran are more complicated. The formula for catamaran hull speed is 1.34*(wetted length)1/2; however, this drag formula is generally not the limiting factor for catamaran hull speed. This is because boats with waterline length to beam ratios greater than 8:1 are not limited by hydrodynamic drag factors, whereas smaller boats need to plane to do so (planing requires enormous amounts of power for displacement hulls). A more important factor to consider is the prismatic coefficient, Cp. Cp = V/(LBP*Am), where V is the volume of water displaced by the hull, LBP is the length between perpendiculars, and Am is the area at midship.

Very fast boats actually require a high prismatic coefficient, which in turn requires a less-narrow boat. However, narrower hulls can get away with a lower prismatic coefficient. The ideal range of Cp for a catamaran is between 0.61 and 0.65. There are a few ways of increasing the prismatic coefficients: sailors can use bulb bows, a wide planing aft segment, or a flat hull rocker in conjunction with a bustle aft. Though high prismatic coefficients increase drag at low speed, at high speeds they can reduce drag by as much as ten percent.

Catamaran Hulls and Low-Wake craft.

As explained here , catamarans can be used to create low-wake ferries. Because of their wide bows and low weights, catamarans can be made to travel quickly with minimal wake. Catamaran ferries are also more fuel-efficient, because of the previously-mentioned factors.

Image Credit: Wikimedia Commons , Catamaran Ferry

Catamaran Boat Design

Hull Speed Calculations

Catamaran Hull Comparisons

Boat Speed Calculator| Know Your Knotts Speed

calculator, calculation, insurance-385506.jpg

Understanding your boat’s speed capabilities is essential for optimizing your sailing experience. Introducing our Boat Speed Calculator – a powerful tool designed to provide you with accurate and valuable insights into your boat’s speed potential.

With our Boat Speed Calculator, you can effortlessly determine how fast your boat can travel based on various factors such as engine power, boat weight, water conditions, and hull design.

Boat Speed Calculator

Whether you’re embarking on a leisurely cruise or racing against the wind, this user-friendly calculator offers real-time speed estimations, helping you plan your journeys with precision and confidence.

Gone are the days of guesswork and estimation. Embrace the efficiency of our Boat Speed Calculator, and unlock a new level of understanding about your boat’s capabilities.

Whether you’re a seasoned captain or a novice sailor, our calculator empowers you with the knowledge to make the most of your boating adventures and enjoy the thrill of cruising through the waters at optimal speed. Discover the possibilities and sail away with confidence, thanks to our advanced Boat Speed Calculator.

How Our Boat Speed Calculator Works

Our Boat Speed Calculator utilizes a sophisticated algorithm that takes into account three crucial factors to provide accurate speed estimations for your watercraft. Firstly, we require the Total Shaft Horsepower (TSH) of the boat’s inboard or outboard engines.

This metric quantifies the combined power output of the engines and directly influences the boat’s speed potential. By inputting this essential value, our calculator can factor in the propulsion force generated by the engines.

Secondly, the weight of the boat plays a significant role in determining its speed capabilities. The calculator considers the total weight of the watercraft, including passengers, fuel, and any additional cargo . This weight data allows our algorithm to calculate the boat’s resistance against the water, a critical aspect in estimating its top speed.

Lastly, the hull type is a key determinant of boat speed. Different hull designs create varying levels of hydrodynamic efficiency, impacting how smoothly the boat glides through the water . By identifying the specific hull type, our Boat Speed Calculator can account for the drag and lift forces acting on the boat, leading to more precise speed estimations.

Once all these essential inputs are provided, our Boat Speed Calculator processes the data through its advanced formula, considering the interplay between horsepower, boat weight, and hull type.

The result is a highly accurate estimation of your boat’s speed potential, allowing you to plan your voyages and boating activities with confidence. Whether you’re looking to cruise at a leisurely pace or push your boat to its maximum speed, our calculator equips you with the information needed to optimize your boating experience and make the most of every nautical journey.

Other Factors

In addition to the three main factors mentioned earlier, several other factors can significantly influence a boat’s speed. Understanding these additional variables provides a comprehensive view of how various elements come together to impact the watercraft’s performance:

Water Conditions: The state of the water body, such as calm seas or rough waves, can affect a boat’s speed. Calm waters allow for smoother navigation and potentially higher speeds, while choppy or turbulent conditions may hinder the boat’s progress.
Wind: Wind speed and direction can either assist or impede a boat’s speed, especially for sailboats. Headwinds can slow down progress, while tailwinds can provide an additional boost to speed.
Boat Load: The number of passengers and the amount of cargo onboard can influence a boat’s speed. Overloading the boat can increase resistance and reduce overall speed.
Trim and Trim Tabs: Properly adjusting the boat’s trim and utilizing trim tabs can optimize its hydrodynamics, leading to improved speed and fuel efficiency.
Boat Maintenance: Regular maintenance and proper care of the boat’s engines and hull contribute to efficient performance and maintain optimal speed capabilities.
Boat Design and Length: The overall design and length of the boat also impact its speed potential. Longer, sleeker hulls with streamlined shapes tend to offer higher speeds compared to bulkier designs.
Water Temperature: Water temperature can influence the boat’s engine performance and efficiency, affecting its overall speed on the water.
Altitude and Elevation: Boating at higher altitudes or in locations with varying elevations can affect engine performance and, subsequently, the boat’s speed.
Tide and Current: The movement of tides and currents can either assist or hinder a boat’s speed, depending on the direction of flow.
Propeller Type: The type and condition of the boat’s propeller can impact its speed and overall efficiency.

Taking into account these additional factors alongside the Total Shaft Horsepower, boat weight, and hull type provides a more comprehensive understanding of a boat’s speed capabilities. By considering all relevant variables, boat owners can make informed decisions, optimize their vessel’s performance, and ensure safe and enjoyable boating experiences on the water.

By considering key factors such as Total Shaft Horsepower, boat weight, hull type, and a range of other influential variables, our calculator provides precise and reliable speed estimations. With our Boat Speed Calculator, you can confidently plan your voyages, races, or leisurely cruises, knowing the optimal speed potential of your boat. Understanding how various elements like water conditions, wind, boatload, and maintenance impact speed allows you to make informed decisions to optimize your vessel’s performance and fuel efficiency.

Clifford Slater is a seasoned writer with over 25 years of experience in boats and fishing trips. With his extensive knowledge and expertise in boats and fishing, he has become a recognized authority in the industry. Clifford has made it a point to regularly visit popular fishing destinations such as Florida and other places in the USA to stay up to date with the latest trends and techniques in the field.

Over the years, Clifford has acquired a wealth of knowledge about boats and fishing, which he has shared through his writing. His articles and books are widely read by fishing enthusiasts and professionals alike, and his insights are highly valued by those seeking to improve their skills in the field. Clifford’s passion for boats and fishing is evident in his writing, and his readers appreciate the depth of his expertise and his ability to communicate complex topics in an engaging and accessible way.

Clifford Slater’s impressive credentials and dedication to his craft make him a trusted authority in the world of boats and fishing. His commitment to staying up to date with the latest developments in the industry, combined with his deep knowledge and understanding of the subject matter, ensures that his writing is always informative and valuable. For those seeking to improve their skills or simply enjoy the beauty of the sea, Clifford’s writing is a must-read.

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Catamaran Hull Type Power Calculations and more

Discussion in ' Boat Design ' started by abdulrahman , Mar 17, 2022 .

abdulrahman Junior Member

Hello everyone, so I am working on a catamaran boat which serves the purpose of cleaning a lake from it's plastic waste etc... basically a lake cleaning robot to be more clear. And after designing the model i now want to find the power needed to power up the system, I did research about it but all i was able to find were not as beneficial to me since it's not in the metric system. i want to find the power equation to calculate it for this hull with dimensions of : 100cm length, 40cm height, 70cm width. And i would like to also ask how am i supposed to do quantitative assumptions for such a thing? some other things that i would love to get some insight about which are : how can i determine the thickness of the material am going to use ? " material that i am thinking of using is PETG with an average density of 1.27 g/cc. how can i determine thrust of the motor i will choose " after determining the power" (below is attached the design and also some calculations that i once tried to do but then found that i cant be using inches and then continue with metric system, i should be sticking to one system for the accuracy of these calculations)

bajansailor Marine Surveyor

Welcome to the Forum Abdul. Is this a university project / exercise or do you actually intend to build a boat to clean waste from the lake? Have you started to build the model yet? Do you have any other drawings showing how the boat will clean up waster - I presume it will have some sort of scoop on the front? I wonder why your transoms are simply 'chopped off' - relatively the hulls will have a bit more resistance like this, when compared to if there was rocker in the hull bottom. I am intrigued by your calculations - do you really need 2 kw to drive a 1 metre long lightweight catamaran? And do your electric motors really work at 28,000 rpm? What speed of rotation do you anticipate the propellers will be turning at?

BlueBell . . . _ _ _ . . . _ _ _

Welcome Abdul, What voltage are you running at 28,000 RPM's?

fredrosse USACE Steam

Quick and very approximate numbers for displacement craft. Displacement speed (knots) = 1.2 * SQRT( Length Waterline (Feet)) At that speed normal propulsion is about one horsepower per ton of displacement. The power number here can be +/- 50%, but clearly far less power than your calculation. The propeller should be turning maybe 1000 RPM, maybe 2000, but again, far less than your number. Is this craft towing or pushing something relevant to the calculations? Please give details.

fredrosse said: ↑ Quick and very approximate numbers for displacement craft. Displacement speed (knots) = 1.2 * SQRT( Length Waterline (Feet)) At that speed normal propulsion is about one horsepower per ton of displacement. The power number here can be +/- 50%, but clearly far less power than your calculation. The propeller should be turning maybe 1000 RPM, maybe 2000, but again, far less than your number. Is this craft towing or pushing something relevant to the calculations? Please give details. Click to expand...

bajansailor said: ↑ Welcome to the Forum Abdul. Is this a university project / exercise or do you actually intend to build a boat to clean waste from the lake? Have you started to build the model yet? Do you have any other drawings showing how the boat will clean up waster - I presume it will have some sort of scoop on the front? I wonder why your transoms are simply 'chopped off' - relatively the hulls will have a bit more resistance like this, when compared to if there was rocker in the hull bottom. I am intrigued by your calculations - do you really need 2 kw to drive a 1 metre long lightweight catamaran? And do your electric motors really work at 28,000 rpm? What speed of rotation do you anticipate the propellers will be turning at? Click to expand...

WhatsApp Image 2022-03-05 at 7.26.31 PM.jpeg

BlueBell said: ↑ Welcome Abdul, What voltage are you running at 28,000 RPM's? Click to expand...

Abdul, Thank you for your response. I watched the video and have some R/C experience. The video is misleading for you because you have a much longer "hull-length" than just the boat. Your gear you're towing is considered part of your boat length. In addition, your boat weight varies by how much debris you've collected. So, you have a hugely varying boat weight depending how much debris is in the catchment system. Also, your boat speed is going to be much, much lower than the R/C enthusiast's. I suspect you're going to need a much, much lower prop RPM and of a huge diameter. This is not an R/C forum. You may get lucky and find someone on here with lots of R/C experience, it's not me. Can you show your towed gear and how it attaches? Also how it loads and empties, max and min weights of debris. What is your design speed? I don't want to discourage you but an R/C forum may be better suited to help you. BB

BlueBell said: ↑ Abdul, Thank you for your response. I watched the video and have some R/C experience. The video is misleading for you because you have a much longer "hull-length" than just the boat. Your gear you're towing is considered part of your boat length. In addition, your boat weight varies by how much debris you've collected. So, you have a hugely varying boat weight depending how much debris is in the catchment system. Also, your boat speed is going to be much, much lower than the R/C enthusiast's. I suspect you're going to need a much, much lower prop RPM and of a huge diameter. This is not an R/C forum. You may get lucky and find someone on here with lots of R/C experience, it's not me. Can you show your towed gear and how it attaches? Also how it loads and empties, max and min weights of debris. What is your design speed? I don't want to discourage you but an R/C forum may be better suited to help you. BB Click to expand...

Heimfried Senior Member

abdulrahman said: ↑ View attachment 177072 Click to expand...

Heimfried said: ↑ Hi Abdul, regarding your calculation in your opening post, do you understand, that a current draw of 110 A from a battery of 3.3 Ah capacity results in an empty battery after 0.03 h or 1.8 minutes? (Just a theoretical raw number, without regarding a lot of effects.) Click to expand...

That's very basic electric around Ohm's law. If you take a Li battery you can mostly draw 70 per cent of its nominal capacity without shorting its life. So if your battery is rated 3.3 Ah (Ampere hours), 70 % of it is 2,3 Ah. The latter is the really useable capacity assumed you draw a current of only 2,3 A for one hour. Sometimes the nominal capacity is rated related to 0.1 C, which means 230 mA only for ten hours. Read about Peukert's law. https://en.wikipedia.org/wiki/Peukert's_law

Heimfried said: ↑ That's very basic electric around Ohm's law. If you take a Li battery you can mostly draw 70 per cent of its nominal capacity without shorting its life. So if your battery is rated 3.3 Ah (Ampere hours), 70 % of it is 2,3 Ah. The latter is the really useable capacity assumed you draw a current of only 2,3 A for one hour. Sometimes the nominal capacity is rated related to 0.1 C, which means 230 mA only for ten hours. Read about Peukert's law. https://en.wikipedia.org/wiki/Peukert's_law Click to expand...

6200 mAh = 6.2 Ah ; 6.2 Ah * 70/100 = 4.3 Ah usable capacity current 110 A means: 4.3 Ah / 110 A = 0.04 h = 2.3 minutes. So battery is empty after around 2 minutes. The nominal rpm of such RC motors is measured with no load at all, free spinning rotor. If you fit a propeller on it and operate it in the water rpm will be about 30 % of the nominal value (this depends heavily on the conditions). The result of your formula V = 2*pi*r * N / 60 is not a velocity but the lenghts of the path which one of the propeller blade tips is decribing in one second (multiple circumferences of the circle). You can not simply suppose that your 28000 rpm motor, reduced to 1,5 % of its rpm will be able to turn the boats prop in real conditions. It needs a minimum of torque for this. Plastic debris in a net towed by a boat may not weigh much but produces a huge drag because of the "irregular forms" and the random orientations of the debris pieces (e.g. cups with opening ahead and such things). This must be included in the calculations regarding the boats drive.

Dolfiman Senior Member

I propose you here attached an alternative design within your dimension (L 1,0 m x B 0,7 m x H 0,4 m) and targeted weight (30 kg), with a good dose of rocker so that to reduce the immersed transom area and its related drag. I give the hydrostatics for 4 drafts covering displacement from 15,7 to 38 kg. And also a preliminary estimation of the drag and of the power estimation (for D 30 kg) using "SA-VPP power catamaran" application, althought the conditions of validity are not fulfilled (for Froude > 0,4 part of the application). More on the application here : SA-VPP power catamaran | Boat Design Net Anyway, for the drag better knowledge, and before fixing the power to install, I strongly recommend you to test at scale one your catamaran in operative conditions, which should not be very difficult in any standard towing tank or calm water area due to the small size and weight. To note that the preliminary estimation shows a high jump of power from 2 to 3 Knots (Froude 0,33 to 0,49).

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Cata 1m_preliminary.pdf

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Calculate your boat top speed with this formula

Jul 03, 2020

less than a min

Calculate your boat top speed with this formula

As a boat owner, you are required or at least expected to have a general knowledge of what a boat speed calculator is, or how a boat speed formula works. This information is important in order to know the capacity of your vessel and what it is worth.

Whether it is a catamaran that you have, a yacht or a sailboat, it is always safer to figure out how fast you can go on water through a boat top speed calculator . Knowing this information can help you look after your boat better, as well as advertise it properly if you want to sell it. Most importantly, however, by figuring out the top speed of your boat you can travel within the limits and always have a safe voyage.

Generally, there are many factors that affect a boat’s top speed. This makes it hard to determine the proper and accurate highest speed. However, different formulas have been generated to help in this task. They allow boat owners to create an idea of how fast their vessel is and how much they can push it on water. One of these formulas is as below:

Boat Speed = The Square Root of ( Shaft Horsepower / Weight ) x Constant

Understanding the boat top speed calculator

In today’s digitally advanced world it is very easy to calculate how fast your vessel can go through various online boat speed calculators . Using a boat speed formula, however, allows you to be more precise when inserting the factors and the data pertaining to your own boat. It might be a longer and more complex method of calculation but it will give you the best results.

When using the above boat speed formula bear in mind that:

The weight is the actual running weight, including anything on the boat from the crew to the engine and fuel.
The shaft horsepower is determined as the engine horsepower without the losses of the drive train.
The constant , on the other hand, are typically calculated from private tests.

Another simple way to calculate the boat top speed or also known as the hull speed is by using this boat speed formula:

Boat Speed = 1.34 x The Square Root of Waterline Length

The waterline length is measured in feet while the boat speed is calculated in knots.

By knowing the top speed of boats, you can then compare different vessels and decide which one is worth buying. In addition, if you are looking to sell your boat, you can negotiate a better price by having all the information in front of you. You can also use TheBoatDB to search and compare boats in order to make an informed decision before making a purchase or a sale.

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Boat Speed Calculator

Haris is a passionate information technology student who likes to ease the problems of others in all spheres of life. In his free time, he prefers to read and write texts. He also has feelings for strategy games and music. Communicative, ambitious, creative, responsible, dedicated and motivated person to work. Socially engaged with a lot of experience in youth work, public relations and project planning.

Last updated: March 1, 2023

We offer you a wide variety of specifically made calculators for free! Click button below to load interactive part of the website.

Table of Contents:

What is a boat?

What is boat displacement, what is the crouch constant, boat speed units, how to use the boat speed calculator.

Wondering how fast a boat can go? Confused by all the boat speed terms out there, like knot and nautical mile per hour? Use our calculator to convert knots to miles/hour, get an estimated theoretical maximum speed for your boat, plus estimate its trim and how far it will travel in a certain amount of time.

A boat (also called a vessel) is a human-powered or motorized watercraft used for transport or recreation. There are many types of boats, ranging from canoes to cruise ships. Boats were invented by humans, who first made logs and pieces of wood into watercraft to cross rivers and lakes. The oldest known boats date back to 8,000 years ago in Africa

The weight of the water displaced by a vessel is its displacement . Displacement is measured in tonnes and not pounds, which might seem confusing at first, but you’ll get used to it. When we say that a boat has a displacement of 10 tonnes, we’re saying that if this boat were placed in open water with no other boats around, it would displace 10 tonnes of water.

The Crouch constant is a numerical value that is used in the boat speed formula to calculate the speed of a boat. It was named after naval architect David Crouch, who first used this specific type of constant in his calculations. This particular constant is used when calculating how fast a ship travels through water based on its hull design and size.

The boat speed calculator can convert your speed from one unit to another. Here are the units it supports:

Knots (nautical miles per hour) – 1 knot = 1.852 kilometers per hour, 0.514 meters per second or 0.5144 miles per hour (1 mile is equivalent to 1760 yards).
Kilometers/hour – 1 kilometer is equivalent to 0.62137 miles or 3281 feet and 35 seconds, which makes it easy to do conversion calculations with a simple mental trick: multiply by 1000 (1000m = 1km), then add 3280ft or 5 feet for every third meter; this will give you an approximate answer that you can round up or down as needed with no problem whatsoever
Miles/hour – You can also use this calculator with your favorite imperial units like kilometers/hour but if that doesn’t work out well for you then don’t worry because both km/h & mph numbers have their own individual units within the same system where they belong

The boat speed calculator can calculate the top speed on your boat based on its:

Shaft horsepower
Displacement

There are 9 types of boats:

Passenger vessels
Average runabouts
Light high-speed cruisers
High-speed runabouts
Racing boats
Hydroplanes
Racing catamarans

The formula also involves the Crouch’s constant, which is 150. Once all values are input, the calculator can give you the theoretical top speed of the boat.

A boat (also called a vessel) is a human-powered or motorized watercraft used for transport or recreation.

What is the fastest boat?

The Spirit of Australia is generally considered to be the fastest boat.

What determines boat speed?

Boat speed is determined by the boat type, boat displacement, and horsepower.

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Curious how the EP Carry outboard will perform on your dinghy or small boat? We’ve created a boat speed and range calculator to help answer that question.

Use the type 1 category for traditional style rowboats, dories with a broad transom, and skinny sailboats like sailing catamarans. Other rigid-hull types should use the "type 2" designation.

Type 1 hulls are designed for efficiency which comes from a relatively long waterline/ overall length ratio, a narrow waterline beam, a clean entry, and a flatter run aft. They take weight well and are comparatively dry in rough conditions. This category often displays low initial stability but generous reserve stability. In other words, it may feel unstable at first, but their resistance to leaning increases as the lean angle increases.

Use this category for prams, double enders like peapods, kayaks and canoes.

Type 2 hulls are characterized as having more buoyancy in the middle compared to type 1. This can come from a generous rocker as you will find in a pram, or having two pointy ends like a pea pod, canoe or kayak. While this type of hull is very efficient and seaworthy they produce a higher resistance when driven above "hull-speed".

Type 3 hulls is a category just for inflatable dinghies. These include RIBs, inflatable floor, and aluminum slat, and plywood floor types, both pointy in the front as well as the new "catamaran" types. On all modern inflatables, the transom is positioned forward of the aft tube ends. This shortens the LWL resulting in the lowest speed relative to boat length for all types listed. All inflatable styles produce similar speeds for their lengths, but RIBs track better in a turn or crosswind. For all inflatables, max speed is particularly weight sensitive and they can be wet in rough conditions, but considering their generous initial stability, inflatables are the comfy choice for families or those who want that extra stable feel.

About the EP Carry speed & range calculator

We promise our speed predictions are at least within +- 10% on speed and range (see assumptions below). Here are some comparisons of predictions vs. measurements:

Customers report being impressed with their performance on the first outing*. If your application is for a boat longer than 13ft or heavier than 600lb loaded, Please contact us before purchase to make sure EP Carry is a good fit for your needs.

Assumptions

Predictions made using the calculator assume normal standard power firmware*. Values are provided for calm conditions, with weight balanced front to back and from side to side. Speed and range is reduced/increased by wind, seas and currents. See FAQ for more info.

* EP Carry offers a free firmware upgrade to 25% more power that may be appropriate for driving boats over 13ft and 600 lb (see Update Firmware ). You can install this yourself using a smart phone.

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COMMENTS

Catamaran Hull Speed Calculator For Beginners (Table and Free
This is the formula for Maximum Hull Speed on a displacement boat: Max hull speed= √((Length on Water Line x g) /(2 x pi)) x 3600/1852. Now we need to add the increased efficiency (loss of drag) of a semi-displacement hull, usually, this is somewhere between a 10-30% increase. Semi Displacement hull speed = Maximum hull speed * 1.3.
Hull Speed Calculator
How to calculate hull speed. The formula for hull speed only needs the length of the vessel's waterline in feet, denoted as L_\text {waterline} Lwaterline. With this length, the vessel's hull speed in knots can be calculated with. V_\text {hull} = 1.34 \sqrt {L_\text {waterline}} V hull = 1.34 Lwaterline. If you want to instead work out exactly ...
Hull Speed Calculator
The formula for calculating the hull speed is as follows: Hull Speed (HS) = 1.34 x √ (LWL) Where: Hull Speed (HS) is the estimated maximum speed of the boat in knots (nautical miles per hour). LWL is the length of the waterline of the boat, typically measured in feet or meters. The factor 1.34 in the formula is an approximation, and it is ...
Catamaran Hull Design
If you have fine hulls you can use a lower Cp. Most monohulls have a Cp of 0.55- 0.57. And that is about right for displacement speeds. However the key to Catamaran design is you need a higher Cp if you want to sail fast. So a multihull should be at least 0.61 and a heavy displacement multihull a bit higher still.
Catamaran Design Formulas
While the length/beam ratio of catamaran, L BRC is between 2.2 and 3.2, a catamaran can be certified to A category if SF > 40 000 and to B category if SF > 15 000. Engine Power Requirements: P m = 4 x (m LDC /1025)P m = 28: The engine power needed for the catamaran is typically 4 kW/tonne and the motoring speed is near the hull speed.
Crouch's Calculator
This useful calculator computes an estimate of boat speed for a modern planing monohull using inputs of the power at the propeller shaft, the total boat weight, and a coefficient called the hull factor. The calculator can also compute any one parameter from the other three parameters—a most useful feature. The hull factor for predicting speed ...
How Fast Do Catamarans Go?
August 30, 2022. ‍ Catamarans are known for their speed, and some vessels are fast enough to break world sailing speed records. Catamarans can go between 15 and 30 knots, with the fastest achieving speeds well in excess of 60 knots. Sailing catamarans are sometimes twice as fast as monohulls and cut through the water with greater efficiency.
Understanding Hull Speed
For example, in the design phase of a cargo ship, engineers need to calculate the hull speed to determine the most efficient hull shape and length. This calculation ensures that the ship can carry the maximum amount of cargo while using the least amount of fuel, thus maximizing profits. Furthermore, in sailing races, skippers use the concept of ...
Hull Speed Calculator
Hull Speed Formula. The following formula is used to calculate a hull speed: HS = 1.35 * SQRT (WL) H S = 1.35 ∗ SQRT (W L) Where HS is the hull speed (MPH) WL is the water line (ft) This formula is only an estimate. The true speed depends on the weight and shape of a hull as well.
Boat Speed Calculator
Calculate the speed of a racing hydroplane having an engine that delivers 3000 hp and displaces 6800 pounds of water.. To calculate boat speed:. Step 1: Enter shaft horsepower value P = 3000 hp.. Step 2: Insert the boat's displacement, D = 6800 lbs.. Step 3: Choose the Crouch constant, C from the list for hydroplanes, i.e., C = 220.. Step 4: Using the Crouch's formula:
Go-Fast.com > Knowledge base > Boat Speed calculator
Catamaran: Pleasure type cat: 275: 6 - 8 %: Fast Catamaran: Late Skater full race, etc: 300 + ... You can then see what effect changes to weight or power will have on top speed. Using the calculator in this fashion will produce surprisingly accurate results. Boat Speed Calculator. Weight: Total Shaft Horsepower: Constant: Speed:
Planing Boat Speed Calculator
Planing Boat Speed Calculator. September 22, 2023 by GEGCalculators. Planing boat speeds vary based on factors like size and design. Smaller boats around 12 feet may plane at 8-10 knots (9-12 mph), while larger 40-foot boats can plane at 35-45 knots (40-52 mph). These estimates are approximate and subject to variation due to hull shape, weight ...
Hull Speed Calculator
The calculation uses a simple formula based on the boat's waterline length. Here is the hull speed formula: Hull Speed (knots) = 1.34 x √Waterline Length (feet) So, for example, a boat with a waterline length of 20 feet would have a theoretical hull speed of: 1.34 x √20 = 8.2 kn. This formula shows that hull speed increases with the ...
Boat Speed Calculator
Horsepower = (speed/ crouch) squared x displacement. HP = (50/150) squared x 800. HP = 88.89. In this case, with your small boat displacing 800 lbs, if you want to reach 50 miles per hour, then you need a 90 hp engine. One thing to remember about upgrading an engine is weight.
PACKET CAT 35 (ISLAND PACKET)
Hull Speed: The maximum speed of a displacement hull (referring to a hull that travels through the water rather than on top of it, e.g. planing). HS = 1.34 x √LWL (in feet) Pounds per Inch Immersion: The weight required to sink the yacht one inch. Calculated by multiplying the LWL area by 5.333 for sea water or 5.2 for fresh water.
Advantages of Catamarans and Catamaran Hull Speeds Calculation
Catamaran hull speeds are very high due to several factors. The advantages of catamarans are great, resulting in fast speeds. Open bridgedeck catamaran hull speeds are not the limiting factor on speed, and many catamarans routinely exceed the hull speed calculation. Lightweight Catamaran hulls can be very speedy and efficient, traveling quickly even with low wind speed.
Boat Speed Calculator| Know Your Knotts Speed
Our Boat Speed Calculator utilizes a sophisticated algorithm that takes into account three crucial factors to provide accurate speed estimations for your watercraft. Firstly, we require the Total Shaft Horsepower (TSH) of the boat's inboard or outboard engines. This metric quantifies the combined power output of the engines and directly ...
Catamaran Hull Type Power Calculations and more
Quick and very approximate numbers for displacement craft. Displacement speed (knots) = 1.2 * SQRT ( Length Waterline (Feet)) At that speed normal propulsion is about one horsepower per ton of displacement. The power number here can be +/- 50%, but clearly far less power than your calculation.
Calculate your boat top speed with this formula
Boat Speed = 1.34 x The Square Root of Waterline Length. The waterline length is measured in feet while the boat speed is calculated in knots. By knowing the top speed of boats, you can then compare different vessels and decide which one is worth buying. In addition, if you are looking to sell your boat, you can negotiate a better price by ...
Boat Speed Calculator
Boat speed units. The boat speed calculator can convert your speed from one unit to another. Here are the units it supports: Knots (nautical miles per hour) - 1 knot = 1.852 kilometers per hour, 0.514 meters per second or 0.5144 miles per hour (1 mile is equivalent to 1760 yards).
About the EP Carry speed & range calculator
Use the type 1 category for traditional style rowboats, dories with a broad transom, and skinny sailboats like sailing catamarans. Other rigid-hull types should use the "type 2" designation. ... About the EP Carry speed & range calculator. We promise our speed predictions are at least within +- 10&percnt; on speed and range (see assumptions ...
Calculating power requirements for catamaran.
Re: Calculating power requirements for catamaran. The Ex40 harryproa is an improvement on the original harry, which was 12m (40') long, 6.75 m (22'3″) wide, weighed 800 kg (1764 lbs) with payload 800 kg (1764 lbs). The lee hull was 500mm wide at the waterline, giving 20:1 length to beam ratio.

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What is boat speed — Calculating using Crouch's formula?

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Crouch constant

How to calculate boat speed using this calculator?

Example of using the boat speed calculator

How do I calculate a boat's top speed?

What is Crouch's formula?

What is the value of Crouch's constant for a racing boat?

What is the value of Crouch's constant for runabout boats?

Boat Speed Predictions

Boat Speed Calculator

Planing Boat Speed Calculator

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Hull Speed Calculator

Key Takeaways

How to Calculate Hull Speed? The Displacement Hull Speed Formula

Using the Hull Speed Calculator

What Causes the Displacement Speed Limit?

Why Does Hull Speed Matter for Your Boat?

Vessel Hull Speed Chart & Table

Final Thoughts

Anchor in Deep Water: Tips and Techniques

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Boat Speed Calculator