Failure occurred because a small drive belt that connected the console throttle lever components to an electrical potentiometer failed
Little things, sometimes not included in routine maintenance, can cause big problems warns the US Coast Guard in a Safety Alert. A worn drive belt and loose nuts that went unnoticed are among the example that led to close calls that could easily have become casualties.
One example concerns a two-decades-old bulker which was leaving port when its main engine throttle failed. It managed to drop anchor without incident.
It happened because a small drive belt that connected the console throttle lever components to an electrical potentiometer failed. Movement of the throttle causes the potentiometer to move and creates a variable signal to other controls which manage engine speed. When the belt failed the control from the engine room console was lost. Fortunately, the vessel had a spare belt that the engineers replaced quickly.
The underside of the Bosch/Rexroth throttle was encased and the belt was not visible under normal circumstances. It was not routinely inspected.
Other cases include: A contact in a small electrical relay and part of the autopilot system stuck and caused a vessel to go hard to port at 24 knots; Three of four nuts on a propeller shaft seal loosened, went unnoticed and caused flooding of the machinery space of an Offshore Supply vessel; A wire chafed and grounded out cutting power to critical combustion controls while a vessel was at the dock, but not long after transiting a narrow Caribbean harbour entrance.
Identifying every single failure mode that could affect a vessel’s propulsion, power generation system or steering system and developing a comprehensive preventative maintenance system for such systems, equipment and components is a very complex task. All the same, it’s worth think about and identifying high risk components which, if a failure or malfunction occurs, could result in a casualty, especially components subject to gradual wear and tear or loosening. Once identified responsible personnel should refer to their respective manuals to determine proper maintenance requirements and take the necessary steps to prevent a future problem.