Investigation and Optimisation of Boat Deployment Systems at High Seas

Abstract

There is a multitude of seagoing missions such as rescue missions, coast guard and pilot duties, whose success depend on ship-deployed boats. Launching these boats from a mother ship or recovering them by special deployment systems in a broad range of environmental conditions are key operations for a successive mission. In recent years, new boat deployment systems, promising better operational availability at high sea states, have evolved beyond the traditional side-davit system with dual falls. These new systems deploy their boats via stern ramps integrated into the transom of the mother ship, for example seen at numerous rescue cruisers around the world. This paper presents two different boat deployment systems. After a short discussion of the disadvantages of side-davit systems, a new type of a stern boat deployment device, the so called Janssen Docking System [1], is introduced. This system is equipped with an articulated ramp hinged to the stern. Whereas launching operations are less critical, the recovery of boats is quite hazardous. For this operation mode structural forces on critical areas as well as the relative motions between the ramp and the small boat are systematically investigated in model tests. Based on the results of these sea keeping tests the feasibility of the system has been analysed and improvements are recommended. As a second system a floodable dock integrated into a mother ship is presented. For launching and recovering small boats at high seas the swell inside the dock and the resulting relative motions between boat and dock ship are investigated. This leads to critical flow conditions inside the harbour in terms of sloshing waves with heights up to 3 meters. The analysis of local flow phenomena inside the dock dependent on the motion of the ship in a given sea state are the basis for the development of an optimized dock shape. Therefore an existing nonlinear numerical method for unsteady viscous computation based on Volume of Fluid (VOF) methods and Reynolds Averaged Navier Stokes Equations (RANSE) is used to simulate these phenomena. The time domain calculation allows to change local dock shapes systematically for further improvements. To validate the numerical solution the calculated results are compared to sea keeping tests at model scale. The paper concludes with a perspective for the further development of the dock shape.