| To those well-performed hull shapes, one may intend to lengthen their parallel middle bodies _lo increase load capacity. But in the modification of ship length, the resistance of the lengthened ship needs to be estimated quickly so that the ship speed can be known. In this paper, the parallel middle body of a 16500 DWT bulk carrier is increased so that the ship is changed into a 24400 DWT bulk carrier. Some kinds of resistance estimating methods are used and the results are compared with that of ship model tests and real ship trials. The influence of lengthening parallel middle body on resistance is studied and more practical methods are given. The research methods are as the following: 1. apply Maxsurf software and create 3-D curved ship model to estimate ship resistance and effective horse power; 2. apply some empirical formula to estimate; 3. employ the method based on Noblesse new slender ship theory, analyze wave making resistance, and calculate the frictional resistance by ITTC method, to predict the resistance; 4. analyze the results of ship model tests.The above studies show that, within some range, the coefficient of residual resistance is decreased though the total effective power is increasing. However, the effective horsepower per cubic meters is decreased. So it is evident that, within the calculated range, the increasing of middle body length does not worsen ship resistance; on the contrary, such increasing can be favorable sometimes.f~The comparisons of the predicted results with the model tests and real ship trial turn out that, after the modification of middle body, Maxsurf software and the theoretical methods can be used to not only predict ship speed when the main engine power does not change. But also predict the required engine horsepower when the design speed is kept unchanged. The empirical formulae, however, are much limited.This study is of value in the similar problems of parallel middle body extension, on the purpose of increase ship's payload. |
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