Dynamic Loads on Mechanical Azimuthing Thrusters

Mechanical azimuthing thrusters have been applied in various ship operations in the past decades, such as low speed manoeuvring; dynamic positioning (DP); bollard pull (BP); high speed transit trips and at continuous full power as the main propulsion system of ships. The ship types on which these thrusters are used include tug boats, offshore supply vessels, pipe layers, drill ships, ferries, fast transport vessels, etc. Despite this widely spread use of such thrusters, however, damages on gears and bearings have been reported in some cases. According to the statistics of survey records of classification societies, gear and bearing failures are at the 2nd and the 3 rd place on the failure list of parts of mechanical azimuthing thrusters, right behind the propellers as the No. 1 vulnerable parts, which are exposed directly to sometimes quite harsh environmental conditions.
To help the industries to get insight into the failures, MARIN has initiated a Joint Industry Project (JIP) on the hydrodynamic loads and shaft responses of mechanical azimuthing thrusters, called SHARES JIP. Thruster, gear and bearing manufacturers, shipyards, ship operators and classifications have been teamed up in the JIP. Studies have covered operational investigations, extensive dedicated model tests for dynamic loads and full-scale trials and monitoring on a ship – the largest pipe layer of the world: Allseas’ SOLITAIRE with 10 sets of 5MW azimuthing thrusters. Results of the study are summarized and presented in this paper.