Propulsion Qualities

the performance characteristic of a vessel expressed by the ratio of the power expended in moving the vessel to the vessel’s dimensions and speed. The simplest quantitative index is the ratio of the product of a vessel’s displacement and its speed to the power of the vessel’s engine. This coefficient can be improved by reducing the resistance to the vessel’s motion, by increasing the propulsor efficiency, and by improving the flow of water to the propulsor. The propulsive coefficient is expressed as the ratio of the power supplied to the propulsor device (for instance, to a screw propeller) to the towing power of the vessel; in other words, this is the efficiency of the propulsor device in open water, taking into account the effect on its operation resulting from such factors as the ship’s lines and steering devices.