Tank Tests on a Hull with the Main Step Faired in Planform and Elevation

Abstract

Tank tests were required to find out whether the water characteristics of a hull with a main step, faired in both planform and elevation, were comparable with those of a hull with a conventional Vee or transverse step. Stability diagrams and spray and resistance characteristics were obtained over a large range of loadings (CDelta0 = 0.616 to CDelta0 = 1.440). The fully faired step offers more possibility of designing a longitudinally stable flying boat hull than does the conventional transverse or Vee step, but a hull with such a step is 5 to 10 per cent. less efficient hydrodynamically except at high speed. In order to avoid running too fine at high speed, it is recommended that the centre of gravity should not be more than 0.46b ahead of the apex of the step. The modification to the step planform makes little difference to the main spray characteristics, but increase in all-up-weight reduces wing, tailplane and propeller clearances. The effect of increase in load on the porpoising stability characterictics is to raise both limits, with a tendency for the upper limit to rise more rapidly, but less regularly, than the lower limit. The free-to-trim attitudes also rise with increase in all-up-weight. The planing efficiency of the hull increases with increase of load, especially at high speeds. There is evidence of a second resistance hump at high speeds and also of a critical variation of planing efficiency with attitude under similar conditions.