A theory for asymmetric vessel impact with horizontal impact velocity.

Abstract

The water impact of planing boats operating at high speed is known to cause significant discomfort, loss of control of the vessel, occasional passenger injury and possible capsize. How a planing hull reacts when impacting the water is very important to high performance boat designers. A two-dimensional solution method for water impact of hard chine vessel sections is developed. The method allows for asymmetric vessel geometry and horizontal impact velocity. Interactions between the two asymmetric body sides as well as asymmetric flow effects from the horizontal impact velocity are incorporated into the hydrodynamic impact model. Two types of impact flow are established based on the degree of asymmetry and the ratio of horizontal to vertical impact velocity. Type A impact occurs when the flow stays attached to the hull until it reaches the chines. For Type B impact, the flow on one side of the hull separates from the hull at the keel. The method of vortex distributions is applied for modeling the nonlinear boundary value problem. The solutions are determined from a time-marching procedure and include free-vortex shedding (jet-spraying). The initial conditions are determined from the basic solutions for straight-sided contours with constant impact velocities. The method can be used to solve for sectional slamming loads (including dynamic pressure distributions, lifting forces and restoring moments), and for the jet formation dynamics. Computational results are presented for symmetric and asymmetric sectional contours with constant or variable impact velocities. The dynamic response of a two-dimensional vessel section during impact due to free fall is solved using the present theory. For asymmetric geometry or for cases with horizontal impact velocity, the resultant vertical penetration and self-righting rolling moment are coupled motions. Experimental investigation into initial impact for both Type A and Type B flows is presented and compared with predictions from the present theory.