A novel restraining system for a powerless advancing ship: a combined theoretical and experimental investigation

A novel flexible restraining system is proposed to protect a waterway crossing road, a railway, or a combined bridge when a powerless advancing ship approaches such a structure. Direct collision with principal bridge supports is not addressed under the assumption that the restraining system is located some distance upstream of the non-navigational bridge, assuming the ship cannot engage propulsive system in reverse to reduce the speed of ship advance. Ship-independent seabed-located gravity anchors are to be ultimately dragged to dissipate ship kinetic energy. A mathematical model of the proposed method of restraint is developed and the resulting movements of ship and anchors are predicted for two distinct ship forms. These ships' responses are investigated for initial ship velocity, angle of approach, and point of contact with restraining cable of different investigated spans in the presence and absence of a current. The theoretical simulations agree reasonably well with the related model measurements given the existence of ship sway and yaw motions are not addressed. The results are sufficient to demonstrate the applicability of the proposed system. Predictions and observations suggest that the smaller the restraining cable span and the closer the ship is located to the anchors (initially vertically below the ends of the restraining cable), the more effective is the retraining process