Hull speed is also referred to as displacement speed. It is the measure of the fastest efficient speed of a boat. The speed is approximately equal to the speed of a free surface wave whose wavelength is equal to the waterline length of the boat. The below given is the Hull speed formula to calculate the boat's displacement speed. According to the Displacement speed of a boat formula, multiplying the square root value of boat's waterline length with 1.34 gives the hull speed.
The displacement speed calculated using the Hull speed formula should be considered in the knots units. The hull speed/displacement speed concept is an outdated and new method called Froude number is used in modern naval architecture to measure the efficiency.