THE MANOEUVRABILITY OF LARGE SHIPS

In this paper, presented in June 1978 at a meeting in Trieste, the Author (of the Italcantieri company) gives a detailed account of experimental work aimed at providing designers with information that will assist in the selection of the type and dimensions of rudders for large ships. The investigation embraced rudder design from the viewpoints of ship manoeuvrability, propulsive characteristics of the hull/propeller/rudder system, and influence of stern form. The investigation was made with a model of the 253,000-dwt Esso Italia; this Italcantieri-built tanker has steam-turbine propulsion plant rates at 32,500 hp at 84 propeller rpm. She was chosen because she was a large ship with proportions that might lead to course instability and because performance and manoeuvrability data were available from her model tests and sea trials. A 1:40-scale model (length b.p. 8.27 m) was used. Variants tested included the model with its original V-form stern, and with a stern tending towards a U-form (representing a Diesel-propelled tanker with a semi-balanced rudder); both these stern forms were tested in combination with different designs of rudder, including the original design. Wake surveys and towed and self-propulsion tests were made in an experiment tank, and manoeuvring tests, with the model manned, were made in a lake. The latter tests included turning-circle, pull-out, weave, and zig-zag tests. The methods used in this work are described, and the results are presented in detail and discussed. Order from BSRA as No. 51,928.