Thruster feedback incident
A drive-off position loss was experienced by one of our members’ vessels whilst it was operating in Class 2 alongside a platform. Upon investigation, the cause of the incident was found to be a mechanical failure in the azimuth feedback unit of one of the thrusters. More specifically, a gear wheel driving the feedback potentiometers was found to be severely worn.
The effect of the failure was that, from the information available to the DPO, the affected thruster was functioning correctly, whilst it was actually delivering thrust in a completely false direction. This was sufficient to cause position instability and made it very difficult to determine the correct course of action.
A complicating factor was the fact that the alarm for mismatch between thruster set point and feedback, which had recently been tested and adjusted, did not activate since throughout the incident the thruster appeared to follow the set points.
Fortunately this particular incident did not result in any damage or injury. The company involved has advised vessels using azimuthing thrusters that have a single mechanical drive for the azimuth feedback potentiometer to assess the situation on the vessel and to take preventative measures.
This information was notified to IMCA by Global Maritime BV. Should you require additional information please do not hesitate to contact Jan Frumau of Global Maritime (Tel: +31 (0) 10 2806900 / e-mail: jcf@globalmaritime.nl).
Safety Event
Published: 1 January 2000
Download: 
IMCA SF 01/00
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