Effect of Shallow Water on the Hydrodynamic Characteristics of a Flat-Bottom Planing Surface

An experimental investigation was made on the Langley tank no. 2 monorail to determine the effect of shallow water on the hydrodynamic characteristics of a flat-bottom planing surface. Measurements were taken of lift, drag, and trimming moment at a constant speed over a range of trims, wetted lengths, and clearances between the model and a false bottom in the tank. The values of lift, drag, and trimming moment about the trailing edge of the model all increased with decreasing clearance. The most apparent increases occurred as clearance decreased below 2.5 inches 1 beam. With combinations of high wetted length and high trim, however, the values began to increase at somewhat greater clearances. The lift-drag ratio increased with decreasing clearance for wetted lengths greater than 0.8 beam and trims less than 16 deg. The roach in the wake of the model increased in height and moved farther aft of the model as the clearance decreased. A description of the monorail and its associated apparatus is included in an appendix.