Alternative Methods for the Identification of Hydrodynamic Coefficients from Standard Manoeuvres

The problem of ship manoeuvrability has increasingly grown in consideration in the last decade, both for merchant and naval ships. With regards to merchant ships, the adoption by IMO of the RESOLUTION A.751(18) in 1993 [1] established minimum manoeuvrability standards to grant safety for all seagoing ships. With regards to naval ships, a strong interest has been manifested by NATO NG6, which established a Specialist Team in naval ship manoeuvrability with the aim of developing, at last, a standardised criteria. The work of this ST resulted in a first Working Paper [2] and a subsequent ANEP will be probably published by the end of the present year with a set of preliminary criteria. An estimation of ship manoeuvrability is strongly related to the accuracy in the determination of the hydrodynamic coefficients which specify the mathematical model of ship manoeuvring used in the existing prediction tools. These coefficients are usually estimated, in a preliminary stage of design, from regression formulas based on existing model-test data [3][4], which may lead to inaccurate predictions for non-conventional vessels or ships exceeding the parametric range of the experimental data base. The aim of the work presented in this paper is the development of a method to identify the hydrodynamic coefficients starting from standard experimental results in order to be able to extract data from the wide experimental data-base available (sea and model-tests trials); two different procedure for the identification of the hydrodynamic coefficients will be presented, with the comparison of their merits and shortcomings.