__Optimum Speed Calculations__

Boats have an optimum speed, which is their hull speed. The displacement speed is governed by waterline length.

To calculate the maximum displacement speed of your boat, a theoretical rule of thumb calculation is as follows:

__If the waterline length (WLL) is in metres__:

Maximum speed in knots = 2.43 x the square root of the waterline length (WLL) of the boat in metres.

e.g. for a WLL of 15 metres the maximum speed is 2.43 x √15

= 2.43 x 3.9 = 9.5 knots (maximum hull speed for WLL of 15 metres).

__If the waterline length (WLL) is in feet__:

Maximum speed in knots = 1.37 x the square root of the waterline length (WLL) of the boat in feet.

e.g. for a WLL of 49 feet the maximum speed is 1.37 x √49

= 1.37 x 7 = 9.6 knots (maximum hull speed for WLL of 49 feet).

This is an approximate guide, as the factor varies with different shaped hulls.

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