Lesson Learned: Tanker Encounters Propulsion Control Failure During Approach To Oil Berth


  • A tanker encountered a propulsion control failure during its final approach to an oil berth, resulting in the main engine’s inability to start in the astern direction.
  • Despite testing the propulsion control system before arrival, the issue arose due to a seized air start valve in the closed position.
  • Fortunately, the tugs assisted the tanker in safely docking, and the defective valve was later replaced to restore full engine functionality.

A tanker was making its final approach to an oil berth with two tugs attached and a pilot on board. The crew had tested the propulsion control system before arrival, running the main engine in both ahead and astern directions without issue. As the tanker neared the berth, the pilot requested dead slow astern on the main engine to stem the vessel’s speed. However, the engine could not be started in the astern direction despite numerous attempts.

Identifying the Issue

Under the pilot’s direction, the tugs managed to stop the vessel’s forward movement and safely berth the tanker. Further investigation revealed the problem: the No. 2 cylinder air start valve had seized in the closed position, preventing air injection into that cylinder. This effectively created a dead zone in the starting sequence, inhibiting the engine from starting in the astern direction.

Disassembly and Valve Replacement

Disassembly of the air start valve found that cylinder combustion gases had leaked into the air start system, scoring the balancing piston and causing it to overheat and seize. The faulty valve was replaced with a spare carried on board, restoring the engine’s ability to run both ahead and astern.

Lessons Learned

1. Risk: The failure of a single component in the air start system led to a significant hazard for the ship. Identifying potential hazards and implementing regular maintenance checks is crucial to ensure system reliability.

2. Hazard: Air start valve leakage presents a considerable risk. While the failure prevented the engine from starting, leakage of hot combustion gases into the air start system introduced the risk of an explosion. Early detection and remedy are essential to maintain a safe engine room environment.

3. Plan: The well-planned berthing operation ensured tugs were available to assist the tanker. Although the engine air start system had worked during pre-arrival testing, its unexpected failure was problematic rather than catastrophic due to the presence of the tugs.

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Source: MAIB