In the last years during the boom of the global shipbuilding industry, a considerable amount of mechanical azimuthing thrusters (typically pushing arrangements with ducted propellers and pulling arrangements with open propellers) were manufactured and delivered for various applications on different types of vessels, covering wide ranges of operational profiles. Recently, rather large number of gear and bearing failures were reported with those thrusters only after being used in service for half or one year, irrespective of the thruster manufacturers and the ship operators. Obviously the operation of those mechanical azimuthing thrusters have exceeded the design constraints and limits, which were based on the present understanding of hydrodynamic loads on the thrusters and their shafting systems, including gears and bearings. At least two possible reasons have been identified and blamed to have resulted in those mechanical failures. One of them is the extreme maneuvering with the azimuthing thrusters, including interactions, typically for offshore structures both during transit and at dynamic positioning. The other is the thruster ventilation, which occurs both in DP and also in high speed sailing conditions when located close to the free surface. In both cases, large hydrodynamic loads variations and shafting responses occur, leading to the high level transient dynamic loads on the propeller blades, which transmit through the propeller hub and shaft to the underwater gears, the pinion shaft and its bearings.
objectives & deliverables
In order to enable better designs of safer and more reliable thruster systems onboard special ships, the thruster propulsion systems has to be improved in design hence tuning the system to actual service conditions. This will result in increased lifetime, lower capital cost, lower maintenance cost, lower emissions and lower fuel consumption. Research into the shaft dynamic response of thruster system is needed to reach this goal.
The current tools and methods that are able to simulate the dynamic behavior of a thruster drive train in actual service conditions are partly available, mainly at the classification societies. However, these have limited abilities to predict actual loading during off-design and dynamical conditions. Off-design conditions, like ventilation of thrusters, are known recently to cause damages but are not well understood. SHARES shall aim at a better understanding of loads and responses following from such conditions, making the project beneficial for better design of the complex thruster mechanical system. This reduces the risk of failure of systems, which is a requirement to enable special vessels to operate safely.
The deliverables will be in the form of reports, which should include the following,
- Operational guidelines
- Understanding of the gear and bearing damage mechanism
- Model test results analyses and reports