Incremental resistance coefficient of fast and large vessels for model ship correlation

The purpose of this investigation is to increase the accuracy of the ITTC-57 powering performance method by splitting the incremental resistance coefficient into a sum of several terms. Analyses of published trial trip results indicate that the incremental resistance coefficient for model ship correlation of the ITTC-57 method depends also on hull form parameters. Low block coefficient ships and ships with buttock flow stern or transom stern have lower values of incremental resistance coefficient for model ship correlation than other ships of the same size and speed. On the basis of this observation a set of formulae is proposed, from which the incremental resistance coefficient of the ITTC-57 method can be calculated. The contributions to the incremental resistance coefficient due to hull roughness, ship size and speed are assumed to be conceptually similar to those used in the ITTC-78 method. The set of formulae has been applied to seventeen ships. Twelve ships have been used as the database for developing the method, and five ships as validation cases. Special scaling procedures may be needed for ships with large bow sonar domes or with other appendages of similar form. Waterjets as the propulsor and strongly cavitating conventional propellers seem to have considerable influence on the incremental resistance coefficient as derived from trial trip results.