Mars Report: Electrical Mismatch Causes Grounding
Losing electric power can quickly make a crew lose control of their vessel. In this case, failing to follow the manufacturer's bow thruster settings contributed to losing power and subsequently grounding.
As edited from Canadian TSB report M17C0205
A chemical product carrier was bound upriver and had just exited a lock when the bridge team reported a bow thruster alarm and shutdown. After some difficulty the breaker was reset; the bow thruster came back online and control was restored to the bridge.
Shortly afterwards, the vessel entered another lock. Once through the lock, the bridge team increased speed to approximately 5 knots. The master shut off the bow thruster, but observed a brief fluctuation in the bow thruster’s load indicator. The master restarted the bow thruster in order to verify his observation. At the same moment, the crew standing by on the forecastle heard a loud noise, and the crew in the engine room experienced local vibrations.
The vessel lost all electrical power, and the main engine, bow thruster, and steering gear shut down. The vessel continued to move forward under its own momentum, swinging slowly to port. Shortly thereafter, the emergency generator automatically activated and electricity was restored to the vessel’s essential safety components, including the steering gear.
On master’s orders, the crew standing by on the forecastle let go the starboard anchor with the intention of reducing the vessel’s speed and swinging to port. The rudder was put hard to starboard, and the port anchor was also let go, but the vessel continued to swing to port. A little later, the vessel made contact with the breakwater on the south side of the canal and subsequently ran aground. The vessel’s speed at the time of the grounding was estimated at about 5 knots.
The investigation identified the following unsafe conditions that rendered the vessel vulnerable to a total loss of power:
- The bow thruster’s local circuit breaker trip and time delay settings were higher than the manufacturer’s recommended settings.
- The main circuit breakers for the vessel’s three auxiliary generators were set to the manufacturer’s recommended trip and time delay settings, which were lower than the bow thruster’s local circuit breaker settings, making them unable to accept the higher load.
- The power management system was in harbour mode, which did not provide the vessel with optimum electrical efficiency and protection.
- The manufacturer’s recommended settings are usually safer than individual settings.
- An incorrect setting on one machine could have negative repercussions on another related machine and even for the entire vessel.