Comparison and study of tank tests and sea trial on a double end passenger catamaran with a new type of azimutal propulsion positioned between the two hulls.

In 2001 the author was involved in the project of a passenger ferry catamaran, to be used in the Rio De Janeiro bay to solve the problem of traffic, offering a competitive alternative to the normal way of transportation. (train, buses, private cars) The main goal of the project was to realize a ferry able to minimize the time for manoeuvring and embarking/disembarking the passengers, also considering that the total amount of passengers required was 1300 . The best way to fulfil this goal was to realize a double end catamaran, in order to avoid manoeuvring, and allow the passengers to simply walk trough the ships. A further problem was the request to realize a maximum speed of 18 knots, a speed higher than the usual speed required for this type of ships. Obviously, it was of extreme importance to minimize the costs, so it was extremely important to reduce the weight of the ship, the power and the consumption of the engines, even considering the importance of meeting the most severe requirements in terms of safety. As a consequence of these parameters the ship was realized completely in Aluminium alloy, with 2 diesel engines MTU type to give power to 2 azimutal propellers at midship with a new system for Catamaran. The study was developed by the Author trough a first series of resistance tests , to define the better solutions in terms of hulls geometry, then another series was developed to optimize the position of the 2 propellers and the shape of the semi hulls who act as a support for the azimutal propellers and the engines. Finally the ferry was delivered and the sea trial gave a final results. The work of the author has been directed to organize the test performed covering different configurations in order to focus on the main aspects of this kind of realizations. The positioning of the 2 azimuthal propulsor is of special interest.After tank test investigations the propulsors were positioned along the longitudinal axis, between the two hulls . This new configuration allows the 2 propulsors to operate in a situation more similar to the one of “Open water propeller” than to the one of “Propeller behind the hull”. This configuration needs to be studied with special care for propulsion problems and manoeuvrability. This situation was investigated in Krilov Institute. The Author studied the appendage to support the azimuthal propeller also with CFD method. In conclusion the Author make an analysis of tank previsions and sea trials results to validate the theoretical study.