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Boat Speed Formula:
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The boat propeller speed formula, known as Crouch's formula, estimates the theoretical top speed of a boat based on horsepower, displacement, and a constant factor that accounts for hull type and efficiency.
The calculator uses Crouch's formula:
Where:
Explanation: The formula shows that speed increases with the square root of the power-to-weight ratio, modified by the hull efficiency factor (Crouch constant).
Details: Accurate speed estimation helps in boat design, propeller selection, performance prediction, and fuel efficiency planning. It's essential for marine engineers, boat builders, and enthusiasts.
Tips: Enter horsepower in hp, displacement in pounds, and select appropriate Crouch constant. Typical Crouch constants: 150 for average runabouts, 180-220 for high-speed planing hulls, 110-130 for displacement hulls.
Q1: What is the Crouch constant?
A: The Crouch constant is an empirical factor that accounts for hull efficiency. Higher values indicate more efficient hull designs capable of higher speeds for given power.
Q2: How accurate is this formula?
A: It provides a good theoretical estimate but actual speed may vary due to factors like water conditions, hull cleanliness, propeller efficiency, and load distribution.
Q3: What are typical Crouch constant values?
A: Displacement hulls: 110-130, Average runabouts: 150, High-performance boats: 180-220, Racing boats: 220+.
Q4: Can this formula be used for all boat types?
A: It works best for planing hulls. For displacement hulls, hull speed limitations apply and the formula may overestimate actual speed.
Q5: How does displacement affect speed?
A: Higher displacement requires more power to achieve the same speed. The relationship is inverse-square root, meaning doubling displacement reduces speed by about 30%.