Forces and velocity measurements in ship propulsion systems

Abstract

Pod drives are modern outboard ship propulsion systems with a motor encapsulated in a watertight pod. The motor's shaft is connected directly to one or two propellers. The whole unit hangs from the stern of the ship and rotates azimuthally, thus providing thrust and steering. In the past decade pod drive propulsion has developed to be a reliable and serious alternative to conventional ship propulsion, especially for cruiser liners. The overall efficiency of the system is determinant for the economical success of the vessel and for this reason it is necessary to improve the efficiency of the propulsor recurring to non-conventional solutions. Force and phase-resolved LDA measurements were performed for inline co-rotating and contra-rotating propeller pod drive models. The measurements permitted to characterize these ship propulsion systems in terms of their hydrodynamic performance and lead to their efficiency optimization. The most efficient co- and contra-rotating propellers were subjected to detailed study of the swirling wake flow by means of laser Doppler anemometry.