Results Of Debris Avoidance Maneuvers & Forward Foil Broaches PCH 1, Buckley, Jun 85(0146)
Calm water trials were conducted using the hydrofoil ship USS HIGH POINT (PCH 1) to determine the effect on foil system loads of both debris avoidance maneuvers and forward foil broaches with symmetric and asymmetric water reentry. Continuous video recordings were made of the hydrodynamic flow over the lower forward strut and foil while local strains were measured in various foil system components. Debris avoidance maneuvers resulted in forward strut hydrodynamic loadings that approached the maximum attainable steady state loadings determined from model tests of struts having similar airfoil sections. Forward foil broaches-in-turns resulted in asymmetric lift on the forward foil due to the momentary loss of lift on the emergent foil semispan and the subsequent ventilated flow during reentry. A 90 deg. helm broach-in-turn resulted in a persistent asymmetric lift with ventilated flow on one semispan and fully wetted flow on the other. The bending strain at the lower end of the forward strut reached 85% of the largest value measured during broaches in rough seas. Video camera recordings of hydrodynamic flow over the forward foil revealed a variety of conditions including fully and partially ventilated flow, steady and unsteady cavitated flow, and combinations of these. Transient foil system loadings resulted from cavity shedding on the forward strut and forward foil trailing edge flap. Transient loads also acted on the aft foil following the development of ventilated flow on the forward foil.