A chemical/product tanker was approaching its berth; weather conditions were fne, a pilot was on board, and the master was controlling the vessel. The vessel had a single shaft with
a controllable pitch propeller (CPP) and a bow thruster, reports MAIB Safety Digest.
In the final stages of the approach, the master set the CPP control from ‘20 ahead’ to ‘20 astern’ to reduce speed; the bow thruster was also in use. The vessel did not seem to be responding to the CPP, so the master selected ‘40 astern’; however, the vessel then appeared to increase speed. The master decided to abort the berthing and managed to steer the vessel safely back into the river, avoiding the berth and some adjacent obstructions. Meanwhile, the bridge and engine room teams attempted to regain control in
backup and local modes but were unable to do so.
None of the crew’s actions were successful in regaining CPP control, so the master activated the bridge main engine emergency stop and both anchors were dropped as the speed reduced. Despite these actions, the tanker eventually came to rest when it collided with a barge moored in the river. There was no signifcant damage to either vessel.
A post-accident technical investigation found that a CPP hydraulic control valve had
malfunctioned, resulting in a loss of system pressure and consequent loss of propeller pitch control. The defect was determined to be excessive wear and tear on the valve. However, the investigation also identified that, although probably not contributing to the loss of control, some ‘non-approved’ spare parts were found in use on the system. It is important that manufacturer-approved spare parts are used, particularly in critical systems such as propulsion and steering.
Faced with a loss of control in a confned navigational environment, the crew, aided by the
pilot, worked as a team to try to bring the situation under control. The early decision to abort the berthing and steer clear of danger unquestionably avoided a more severe outcome. Dropping the anchor when still making headway can be hazardous but, given the lack of time and space, almost certainly contributed to minimising the consequences of this accident.
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Source: MAIB Safety Digest