posted 29 October 2001 05:10 PM
Does anyone know of the formula for calculating the displacement speed of a boat? I know it’s connected with waterline length but I need the rest of it.
07 November 2001 09:23 PM
I guess that you are thinking of the formula speed = 1.34 x square root(waterline length), where speed is in knots and length is in feet. This is the speed at which the boat is creating a wave with the same wavelength as the length of the boat. Faster than this needs a lot more ooomph or a planing hull, although Tony Marchaj states that a good heavy displacement keelboat can reach a speed of about 1.4 x sqrt(waterline length) and a destroyer can get up to about 2x. If you want to know (lots) more then see Marchaj, Sailing Theory and Practice, published by Adlard Coles.