How do you calculate boat speed?

The formula to calculate the speed is therefore: (L x 60) (T x 100) = V, where L is length in feet, T is time in seconds and V is speed in knots. For example, if on a 28ft yacht it took three and a half seconds to pass an object, the calculation would be : (28 x 60) divided by (3.5 x 100) = 4.8 knots.

What is meant by hull speed?

Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well.