Planing Speed (from Crouch's Formula)

Formula

• Kts = C / square root ( max disp lbs / SHP )

C is a constant, 150 for runabout, 190 for fast, 210 for race, use 150 for ALL displacement craft.

Planing speed isn’t really a great deal of use to to the owner of a displacement craft, but like the other formulae it is included here for completeness.

If we put in the numbers from our example vessel, C of 150, displacement of 10,000 lbs, and 42 SHP we get a speed of 9.76 knots. Since we know that a displacement hull cannot exceed “hull speed” we should be looking for a hull speed somewhat lower than this figure of 9.76 knots.