Propulsive Efficiency of Submarines and Surface Warships over their Operational Speed Ranges

摘要

Surface warships and submarines are required to operate over a range of speeds, unlike merchant ships that are usually optimised for one particular cruising speed. For surface warships, the advance ratio is a function of speed due to the change in the resistance coefficient at different vessel speeds caused by wavemaking resistance and sea conditions. Surface warships are required to operate over a range of speeds, e.g. low speed cruising and high speed sprinting. Thus, their propulsors need to be efficient over a wider range of advance ratios and flow conditions, and the design process must take into account the efficiency at low and high speeds. Deeply submerged submarines maintain a relatively constant advance ratio, and hence constant propulsion efficiency, over their operational speed range. Thus, the non-dimensionalised flow field is essentially the same and independent of speed, enabling the propulsor to be optimised for this condition. This paper uses generic data for submarine and surface warships to show the change in propeller advance ratios with speed. It is seen that changes in a vessel's propulsive efficiency with speed are related to the resistance coefficient, which is influenced by the wave making resistance, propulsor-hull interaction and the propulsor operating point. The paper provides trends on these effects for submarines and surface warships over typical operating conditions. Unlike surface warships, the change in advance ratio for deeply submerged submarines is small over the operating speed range. Thus, the selection and optimisation of the propulsors require different strategies for surface warships and submarines.