Loss of heading control on an FPU during diving operations

During diving operations at an FPU (floating production unit), the forward thruster was isolated, and the turret locked, in line with diving isolation procedures. The starboard aft thruster was out of service due to an ongoing upgrade project. The only thruster in operation and available was the aft port thruster.

During preparation of greasing of the port thruster steering pump, the standby pump did not start automatically. This resulted in there being no azimuth (direction) control of the thruster and loss of heading control of the FPU. The Diving Supervisor on the light daughter craft (LDC) was notified by the FPU control room immediately that they had lost power on one thruster. The Diving Supervisor informed the divers of the situation and confirmed that the divers had a clear route to surface.

Based on the fact that the FPU turret rotation was locked, the Diving Supervisor secured the work site, while the LDC Coxswain monitored the heading. The Diving Supervisor then recovered the divers to surface safely in a controlled manner.

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