Heavy displacement hulls cannot exceed a speed of __ times the square root of the waterline length without requiring excessive power.

Heavy displacement hulls cannot exceed a speed of __ times the square root of the waterline length without requiring excessive power.

• A. 1.20 times the square root of the waterline length
• B. 1.34 times the square root of the waterline length
• C. 2.0 times the square root of the waterline length
• D. 0.75 times the square root of the waterline length

Answer: (B)

Heavy displacement hulls are limited by hull speed—the speed where the hull is riding on its own bow wave. For these hulls, the practical maximum speed is about 1.34 times the square root of the waterline length (in feet), and the speed is measured in knots. This rule of thumb comes from how gravity waves propagate: as you push faster, you must generate longer waves whose wavelength approaches the boat’s waterline length, and the resistance from wave-making climbs rapidly. The 1.34 multiplier captures that relationship in common units, so longer waterlines yield higher hull speeds, but the increase slows as you approach that limit. To see why the other numbers don’t fit, they don’t align with the standard hull-speed relationship. A multiplier of 1.20 would understate the typical limit, 2.0 would imply a much higher practical speed than displacement hull physics usually permits, and 0.75 is far too low to represent the speed at which most displacement hulls begin to require excessive power.

Heavy displacement hulls are limited by hull speed—the speed where the hull is riding on its own bow wave. For these hulls, the practical maximum speed is about 1.34 times the square root of the waterline length (in feet), and the speed is measured in knots. This rule of thumb comes from how gravity waves propagate: as you push faster, you must generate longer waves whose wavelength approaches the boat’s waterline length, and the resistance from wave-making climbs rapidly. The 1.34 multiplier captures that relationship in common units, so longer waterlines yield higher hull speeds, but the increase slows as you approach that limit.

To see why the other numbers don’t fit, they don’t align with the standard hull-speed relationship. A multiplier of 1.20 would understate the typical limit, 2.0 would imply a much higher practical speed than displacement hull physics usually permits, and 0.75 is far too low to represent the speed at which most displacement hulls begin to require excessive power.