Investigating Hull Blockage and Thruster-Hull Effects on an ASD Tug

Abstract

Interactions between a vessel’s hull and its propulsor are important design and engineering considerations. For vessels equipped with azimuthing propulsors, these interactions are compounded due to the ability of propulsors to direct thrust over a wider arc, even into its own hull. In this study, we examine the interactions between a pair of thrusters and the hull of an azimuthing stern drive (ASD) tug. Specifically, we analyse thruster-on-hull effects, which can materialise as increases in hull drag when flow around the hull is altered by a thruster, or when thrust is vectored towards the hull and impeded by hull surfaces. A series of captive model tests were conducted to evaluate these effects using static and dynamic planar motion mechanism (PMM) tests, in both bare hull and appended hull configurations. Results from this study identify the conditions contributing to thruster-on-hull interactions, and provide further insights into physical mechanisms affecting thruster and hull performances in different flow regimes.