The incident reported below resulted in a complete machinery breakdown.
The vessel was preparing to depart from anchorage. The main engine shaft generator was connected to the main switchboard and everything appeared to be normal. One of the engine crew members was working near the engine when he suddenly heard an abnormal noise which sounded like a rising load. A few seconds later the engine started hunting and the engine revolutions increased far above the normal revolutions. All remote and emergency stops were activated, but that seemed to have no impact on the situation. Heavy vibration from the engine and thick smoke from the shaft generator were observed before the shaft generator blacked out, the engine stopped and the fire alarm activated.
Damaged rotor windings.
Damage found and repairs
The vessel was shifted from anchorage to a waiting berth for further inspection and investigation. The normal revolutions for this engine were 800 rpm and investigations revealed that just before the engine stopped, the revolutions could have reached as high as 1,600 rpm. The shaft generator was found completely broken and a new replacement generator was necessary. Furthermore, the crankshaft was found bent and twisted, several of the counter-weights had fallen off due to broken bolts, the connecting rod was distorted, there was scoring noticed on several of the main journals and several of the crankpins had been overheated. The bedplate was also found holed as a result of the incident. A major part of the engine had to be renewed and the bedplate had to be replaced. The vessel was at the repair yard for approximately 40 days carrying out repairs.
Damaged engine bed plate.
Cause of the incident
Investigations concluded that the cause of the over speed was probably a broken cotter pin of the main engine governor drive sleeve and the wrong assembly of the control sleeve to the fuel control rack of two fuel pump units. This resulted in sending a wrong feedback signal to the governor, rendering it incapable of controlling the speed of the main engine. Furthermore, there was also a malfunction of the over speed trip which did not activate when the engine revolutions increased/exceeded the normal revolutions for the engine.
It is imperative that regular overhauling of vital engine parts such as governor/fuel pumps is carried out preferably by maker’s representative, or well-recommended workshops.
It is imperative that the over speed trip is tested on a regular basis in accordance with the ship’s maintenance schedule.
Gard News 186, May/July 2007
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