GB997737A - Reduction in hydrodynamic drag of water buoyant vessels - Google Patents

Abstract

997,737. Reducing skin friction of marine craft. A. P. PEDRICK. May 11, 1964, No. 9653/63. Headings B7A and B7M. In a marine craft which in its movement through water derives substantial buoyancy by reason of the base surface of its hull being at a level below that of the surface of the water through which it is moving, said base surface being over at least part of its length substantially flat, a stream of air is discharged forward of said flat part with a velocity such that its horizontal component in the direction towards the stern of the craft is equal, or nearly equal, to the velocity of the craft so that the air so discharged forms a substantially immobile mass, in the space between the flat base part and the water directly below it, such mass of air being undisturbed by the relative movement over it of any recesses or ridges formed in the base of the craft between the point of discharge of the air and the rear of the base longitudinally directly in line with said point of discharge, beyond which near extremity the air is free to rise upwardly and escape to the surface of the water in which the craft is buoyant. In Figs. 2 and 3 air taken in at 7 is discharged by a pump to below the flat base 1 of the hull which has sloping sides 2, 3. The base is provided with longitudinal fin plates 12. The outflow of air to below the base is regulated manually or automatically, e.g. by plate valves 19 (Fig. 9) adjustable by means 14 in compartments 13. The invention may be applied to existing ships with vertical sides, e.g. by providing a false side 20 (Fig. 13) sealed in airtight manner at the top by a bellows or diaphragm member 21. An alternative method (Fig. 16) is to provide concave, inclined fins 23, each projecting slightly more than the one below it. In Figs. 19 and 20 a windmill 30 drives a compressor 31 from which air is pumped out of ports 32 along the keel of a yacht, which keel has troughs formed by fins 33 running longitudinally thereof. A sculling boat for boat racing may incorporate the invention by one of the crew operating a pump, e.g. a foot operated air compressor, which causes air to flow under the base of the boat from near the bows thereof.