Enter your boat's displacement (weight), engine horsepower, and boat type to calculate its top speed using Crouch's formula. You can also work backwards — enter a known speed to find the Crouch constant for your specific hull. Results include top speed in mph, the Crouch constant, and a visual breakdown.
Estimated Top Speed
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Crouch Constant Used (C)
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Power-to-Weight Ratio
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Your Hull's Crouch Constant (from known speed)
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Crouch's formula calculates a boat's top speed as S = √(P / D) × C, where P is engine horsepower, D is displacement in pounds, and C is the Crouch constant specific to the boat type. It was developed by George Crouch and is widely used for preliminary hull design analysis.
Displacement refers to the total weight of the boat, including the hull, engine, fuel, passengers, and cargo. It represents the weight of water displaced by the boat's hull. For speed calculations, it is measured in pounds (imperial) and directly affects how fast the boat can travel — a heavier boat requires more power to reach the same speed.
The Crouch constant (C) is a value that accounts for hull design efficiency and boat category. Typical values range from 150 for slow cruisers to 240+ for racing boats. If you know your boat's current top speed, horsepower, and weight, you can back-calculate your specific constant using C = S / √(P / D). Enter your known speed in the optional field above to find it.
Enter your boat's total weight (displacement in lbs), engine horsepower, and select your boat type to get the Crouch constant. The calculator then applies S = √(HP / Weight) × C to estimate your top speed in mph. For best accuracy, include all weight onboard including fuel and passengers.
Racing boats typically use a Crouch constant of around 240. This higher value reflects the efficient, lightweight hulls designed specifically to maximize speed. Some purpose-built racing hulls may use constants even higher than 240 depending on their specific design.
Average runabouts typically use a Crouch constant of around 210. Light high-speed cruisers use approximately 220, and high-speed runabouts use around 230. These values reflect the balance between hull efficiency and practical design for recreational use.
Crouch's formula is most accurate for planing hull boats at high speeds. It is less reliable for displacement hulls (like slow cruisers) that operate below planing speed. The formula is best used as a preliminary estimate and is commonly used by boat designers for early-stage hull analysis rather than as a precise engineering specification.
Since speed is proportional to the square root of the power-to-weight ratio, doubling your horsepower does not double your speed — it increases speed by approximately 41%. To significantly increase top speed, you need to either greatly increase horsepower or reduce the boat's displacement (weight), or both.