Crouch Planing-Speed Estimate

Crouch's formula speed = C / sqrt(weight / hp), in MILES PER HOUR (not knots), with the hull constant C about 150 heavy cruiser, 190 runabout, 210 race. A 6,000 lb runabout with 200 hp and C = 190 makes 34.7 mph; double the power to 400 hp and it reaches only 49.1 mph -- twice the horsepower buys sqrt(2) = 41% more speed, not double, because speed scales with the square root of the power-to-weight ratio. Assumes the boat is on plane (below the planing threshold use displacement hull speed). A planning estimate; the hull, propeller, and conditions govern.

speed_mph = C / sqrt(weight_lb / hp), with the hull constant C ~150 heavy cruiser / ~190 runabout / ~210 race.

Crouch's planing-speed formula (naval-architecture back-of-envelope for planing top speed), by name; the actual hull, propeller, and conditions govern.

Crouch's formula is a published naval-architecture estimate; the displacement, horsepower, and hull constant come from the boat and its class.

Estimate. AHJ and licensed professional govern.

Field names used by the API: displacement_lb, shaft_hp, hull_constant, speed_mph

• Units the result is mph, not knots; do not compare directly to a displacement hull speed in knotsCrouch's formula convention
• Square-root return speed scales with sqrt(hp/weight), so doubling power gains about 41%Crouch's formula
• Hull constant C ~150 heavy cruiser, ~190 runabout, ~210 race; it dominates the estimatenaval-architecture practice