Experimental study on Accelerating and Decelerating Ship Motions

Abstract

In the previous report, the longitudinal forces acting on a ship under accelerating or decelerating motion were treated and an estimating method of the transient motion was proposed from a practical point of view.In this report, the lateral forces acting on a ship in the transient motion, and accordingly manoeuvrability are investigated.The model ship tested is a Series 60 parent type (L/B=7.0, CB=0.7) and experiments were carried out in a towing tank using a PMM.As a propeller working effects on a hull and on a rudder are different from each other, it is reasonable to divide the lateral force of a ship into two parts, the rudder force including rudder induced force on a hull and the remainder.Propeller working effects are unexpectedly strong on a hull and can be represented by a simple function of the apparent advance ratio Js, as seen in Fig. 6.The damping force acting on a rudder, in its dimensionless form, is proportional to the parameter k=√1+k8/π·KT/J2, while the turning force is proportional to k2.As a consequence, both longitudinal and lateral hydrodynamic forces on a ship are possible to be represented using Js.Hence, course stability of a ship and rudder effectiveness depend strongly on Js in the transient motion.The results are also confirmed by the free running tests of the model