... The drag of a displacement hull rises as the square of its speed, because of slow speeds the majority of drag is frictional resistance of the water.  As speed increases the resistance, which takes over, is wave making resistance. All displacement boats display wave-making characteristics and suffer from the consequent drag.
      Length to beam ratio (l/b) is the most important factor in determining the degree of wave making resistance.  As speed increases, the waveform that the hull produces rapidly lengthens until it becomes approximately the same length as the immersed part of the hull.  Typically this occurs when the speed in knots is 1.5 times the square root of the water line length in feet. Short and fat sooner than long and slim. When the length of the wave is approximately equal to the length of the craft she suddenly runs into greatly increased resistance due to the fact she is having to climb over her own wave in order to go faster. This is called the "resistance hump".
       To achieve high speeds, a displacement craft has to be as long and thin as possible as in crossbow. The alternative is to find some way of escaping the hump. The best way is planing. Some people think the main advantage of planing is that the boat rises up in the water and consequently reduces the area of wetted surface, but in fact this is no more than a useful extra: the main objective is to escape the clutches of wave making drag. A high power to weight ratio is necessary (p/w) the higher the better.
       Once a planing boat is up it is free to go on increasing its speed unhampered by wave making drag. Upon planing it is generally possible to reduce the wetted surface by 50%. Another marginal advantage is that planing craft tend to force a certain amount of air under the planing surface so that the boat can be said to be running on a foamy air/ water mixture, which has a lower coefficient of friction than pure water.