Preliminary power prediction during early design stages of a ship

Abstract

A need exists whereby the preliminary power requirement of a ship can be rapidly estimated. Because the majority of methods available for this purpose are manual and consist of a number of independent components, they are tedious and time consuming to use. With the advent of the personal computer and its widespread acceptance, it was logical to examine the various components involved to determine their suitability for computerisation and general accuracy. In total eleven hull resistance prediction methods were examined, eight of which were computerised. Model test data of four vessels were used to evaluate these eight programs. The methodproviding the best results was selected to form the core of an integrated Power Prediction program. Factors such as appendage resistance, fouling and hull roughness were examined and appropriate methods selected for inclusion into the integrated program. Various propeller series were examined and evaluated against a variety of examples and model data. Two propeller optimisation programs were written and a general method for determining the optimum characteristics from Kr-KQ polynomials is described. Methods for determining propulsion coefficients were examined and their results compared with those obtained from model tests. The method providing the best overall results was incorporated into the Power Prediction program Added resistance due to sea state was broken down into two components, namely wind and wave resistance. Only the head sea and wind conditions were considered. Various methods for estimating wind resistance were examined and a program developed capable of providing resistance estimates regardless of wind direction. The problem of added resistance due to waves was examined and two programs written around the methods examined. To facilitate prediction estimates, sea state was chosen as the prime function. Wave height is estimated for the appropriate sea state and wind speed in turn from the wave height Actual sea trial data ofa twin screw channel ship is used to determine the overall accuracy ofthe Power Prediction Program