Mohammad Reza Golbahar

Finding the most efficient point of performance for the propulsion system of ships by considering the engine performance curves, cruise speed of the ship, minimum fuel consumption and best maneuverability of the ship is a critical duty of the ship designers. In this paper, a matching propulsion system analysis is performed for a catamaran passenger vessel to determine its efficient point. The studied propulsion system consists of an engine, a reduction gearbox, a shaft, and a fixed-pitch propeller. The effect of gear ratio change on the efficiency, engine performance, and ship speed was investigated, while other propulsion elements were kept the same during the tests. First, numerical methods have been used to calculate the ship resistance at different speeds, and the results have been confirmed by sea trial tests. The consequent experimental analyses were performed by changing the gear ratio of 2.571:1, 2.731:1, 2.963:1, and 3.231:1. The service speed, top speed, engine margin, brake specific fuel consumption, acceleration reserve, and the efficiency of the propulsion system were evaluated and recorded for all the gear ratio conditions. Processing of the results showed that the gear ratio of 2.963:1 has the best efficient for the ship with 20 knots as service speed, 29 knots as top speed, 9.7% engine margin, 20% service margin, 246 lit/h of fuel consumption, and 61.8% efficiency of the propulsion system. Finally, at the selected efficient point, the operating parameter of Mtu12V396TE94 such as coolant temperature, exhaust outlet temperature, and secondary turbocharger activation were controlled to be within the permissible safety range.