Novel combinator surface concept for efficiency optimization of ship propulsion system

Abstract

This paper describes a methodology to design and generate a novel optimal combinator surface suitable for mechanical propulsion systems on ships with controllable-pitch propellers (CPPs). The combinator surface is an extension and enhancement of conventional combinator curves, considering the effect of both the advance speed and the propeller thrust for the selection of optimal operation setpoints for propeller RPM and pitch. The generation of optimal combinator surface does not require the estimation of the ship resistance, wake fraction, and thrust deduction fraction, enabling automatic reference setpoint searching during the steady state as well as acceleration and deceleration. The optimization algorithm is created based on the maximization of the power and propulsion efficiency, taking the prime mover and propeller constraints into consideration. The proposed methodology is illustrated using a longliner as a case study ship. From thrust and ship speed analysis, the proposed combinator surface method benefits vessels working with frequently changing operations. The ship propulsion efficiency is improved greatly for ship acceleration. The comparison of the efficiency performance using the conventional combinator curve and the proposed combinator surface demonstrates that the new concept of combinator surface enables more efficient propulsion for ships operating under varying loading and sea state conditions.