Effect of a high-speed catamaran trim and draft on the value of residual resistance coefficient

The paper studies changes in water resistance to the motion of a high-speed passenger catamaran due to changes in trim and draft. The trim can vary within small limits both during design by changing the arrangement of masses and during operation due to ballasting or the movement of passengers. The draft can also change during the design process due to changes in equipment or inaccuracies in determining the masses, and during project modernization — for example, for operation in another area. During operation, the draft depends on the vessel’s load. Through such variations, it is possible to provide the vessel with better seaworthiness and operational qualities. One way to improve such qualities can be to reduce water resistance to the vessel’s motion, as this can reduce the load on the main engines, decrease fuel consumption, and increase achievable speed. This paper presents the results of a study of the vessel’s trim parameters on the residual resistance coefficient. The tests were carried out in the towing tank at the Admiral Makarov State University of Maritime and Inland Shipping. The paper presents experimentally obtained curves of residual resistance coefficients for four specified values of static trim. The displacement was kept constant and corresponded to the full load of the vessel, and the model’s center of gravity position was changed by transferring ballast. The studies were performed for the case of a landing with maximum operational trim by the stern (the static trim angle was –0.7 degrees, the running trim angle at maximum speed was about –2 degrees), for the case in which the running trim was close to zero (the static trim angle was 1.4 degrees), and for two intermediate variants. The tests were conducted in calm deep water for Froude numbers from 0.41 to 0.82, corresponding to full-scale vessel speeds from 14 to 28 knots. It was shown that the effect of trim on resistance depends on speed. At Froude numbers of 0.40 to 0.55 (full-scale vessel speed of 14–19 knots), trim by the stern increases resistance. At higher speeds, with increasing trim, the value of the residual resistance coefficient decreases, while with increasing speed, the positive effect of trim also increases. The effect of increasing draft on the value of residual resistance with constant trim is also estimated. At low speeds, increasing draft increases the residual resistance coefficient; with increasing draft, this effect decreases. Thus, some trim by the stern allows reducing the value of towing resistance when moving at high speeds in calm deep water.

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