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We made a small-size model (Lpp = 2.50m) of a medium-size bulk carrier (Lpp = 133.00m) together with small twin podded propellers (D= 0.08m). For such a model, it is important but difficult to manufacture a precise dynamometer used for propeller or propulsion tests. Therefore we made a dynamometer to measure only the thrust of the podded propellers. In order to obtain the propulsive performance of the small model ship, we perform the following experiments at Kyushu University, where there is a small towing tank (L*B*d = 120m*2.67m*3m) . 1. Resistance tests of the hull with and without struts and pods. 2. Propeller open-water test of a single propeller. 3. Propeller tests with dummy struts and pods (pusher and tractor types). 4. Propeller tests with real struts and pods (pusher and tractor types). In this case, only thrust is measured. 5. Load varying tests at several ship-propulsion points. From the obtained results, we analyse the propulsive performance by the combined uses of various results. In extrapolation, the pod and strut can be treated as an appendage of the hull or a part of the propulsor. Which treatment is more reasonable ? We wish to discuss on this point. On the other hand, we perform theoretical calculations corresponding to the above experiments to obtain the propulsive performance of the model ship by using a surface panel code which was developed at Kyushu University. By these approaches, we attempt to clarify the mechanism of the propulsive performance the ship model with small twin podded propellers. |
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