Hydrodynamics

Both the lateral and longitudinal lines of a float or hull are designed to achieve a maximum lifting force by diverting the water and the air downward. The forward bottom portion of the float and a hull is designed very much like the bottom surface of a speedboat. The rearward position, however, differs significantly from a speedboat.

A speedboat is designed for travel at an almost constant pitch angle and, therefore, the contour of the entire bottom is constructed in approximately a continuous straight line. However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude.

This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water. The water can then flow freely behind the step, resulting in minimum surface so the seaplane can lift off the water.

The steps are located slightly behind the airplane's center of gravity, approximately at the point where the main wheels of a landplane are located. If the steps were located too far aft or forward at this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planning (rising partly out of the water while moving at high speed) or lift off. Although, steps are necessary, the sharp break along the float's or hull's underside causes structural concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow.