On the Optimization of the Aft-Part of Fine Hull Forms (First Report)

Abstract

The optimization of hull forms of the aft-part of fine hull forms is pursued following the optimization of overall performance of rudders. The investigations on the optimization of rudder configurations and on the development of the Stern-End-Bulb suggest that the aft-part of hull forms of merchant ships has broad possibility to be improved. The main aims are to clarify the potential interactions between a hull and a propeller by theoretical and experimental researches and to develope a new method of designing the aft-part with available theoretical tools. In this first report, two ways of theoretical approach and some experimental results are presented. Firstly, a method of calculating thrust deduction is developed with the double model flow theory, Lagalley's theorem and pressure integration. This method is applied to a container model ship and a modified hull form is designed. Calculations and experiments on the original and modified model ships indicate the simultaneous improvements of thrust deduction and wake fraction. They also clarify the components of thrust deduction. Secondly, a new method of calculating the inviscid resistance of propelling ships is developed. This method is based on the linear wave making theory in which singularities are distributed on the hull surface together with the propeller disk plane. It is verified with extensive experiments that this method is excellently effective for the theoretical explanation of thrust deduction and for the calculation of inviscid resistance of propelling ships. The effect of waves cannot be neglected in the evaluation of thrust deduction for moderate and high speed ships.