Displacement Hull Speed Calculator

Hull Speed Formula:

\[ Hull\ Speed = 1.34 \times \sqrt{LWL} \]

Hull Speed:

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1. What is Hull Speed?

Hull speed is the theoretical maximum speed that a displacement hull boat can achieve without planing. It represents the speed at which the wavelength of the boat's bow wave equals the boat's waterline length, creating significant wave-making resistance.

2. How Does the Calculator Work?

The calculator uses the Hull Speed formula:

\[ Hull\ Speed = 1.34 \times \sqrt{LWL} \]

Where:

\( Hull\ Speed \) — Maximum theoretical speed in knots
\( LWL \) — Length at waterline in feet
\( 1.34 \) — Empirical coefficient for displacement hulls

Explanation: The formula is based on the relationship between a boat's waterline length and the wave pattern it creates. As speed increases, the wavelength of the bow wave increases until it matches the boat's length, creating maximum resistance.

3. Importance of Hull Speed Calculation

Details: Understanding hull speed is crucial for boat design, performance prediction, and efficient operation. It helps determine the practical speed limits for displacement vessels and informs decisions about engine power and fuel consumption.

4. Using the Calculator

Tips: Enter the boat's length at waterline (LWL) in feet. This is the length of the boat at the waterline, not the overall length. The value must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What types of boats does this apply to?
A: This formula applies specifically to displacement hull boats, which include most sailboats, trawlers, and traditional motor yachts that move through rather than on top of the water.

Q2: Can boats exceed their hull speed?
A: Yes, with sufficient power, some displacement boats can exceed hull speed, but fuel consumption increases dramatically. Planing hulls are designed to overcome this limitation.

Q3: Why is the coefficient 1.34?
A: The coefficient 1.34 is an empirical value derived from wave theory and practical observation. It represents the speed-length ratio where wave-making resistance becomes dominant.

Q4: How accurate is this calculation?
A: The formula provides a good theoretical estimate, but actual performance can vary based on hull shape, weight distribution, sea conditions, and other factors.

Q5: Does this apply to metric measurements?
A: The formula is designed for imperial units (feet and knots). For metric (meters and km/h), the coefficient changes to approximately 2.43.