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Marine Safety Information Letter No. 04/17

Overheating of hydrodynamic fluid coupling and subsequent fire

Place du Centre
200 Promenade du Portage, 4th Floor
Gatineau QC  K1A 1K8

14 December 2017

Safety advisory letter no. 04/17
Related occurrence: M17C0220

Letter addressed to Transport Canada

Subject: Marine Safety Information Letter No. 04/17 – Overheating of hydrodynamic fluid coupling and subsequent fire

On 15 September 2017, the tug Brochu, with 3 people on board, sustained a starboard fluid coupling malfunction resulting in a fire in the engine compartment. Using its port engine, the tug returned to its berth where fire fighters and the tug's crew extinguished the fire. No injuries or pollution were reported but the fire caused extensive damage to the tug. The Transportation Safety Board of Canada (TSB) investigation into this occurrence is ongoing (TSB Occurrence M17C0220).

The tug is equipped with 2 cycloidal propellers coupled to 2 main engines by 2 hydrodynamic fluid couplings. Each fluid coupling is equipped with a mechanical thermal switch that will trigger an audible and visual alarm to alert the operator when the couplings overheat. The fluid coupling is also equipped with three fusible plugs that melt when the temperature reaches a higher preset value in order to drain the coupling oil, which stops all power transmission thus preventing excessive pressure build-up inside the coupling.

On the day of the occurrence, the tug Brochu and a sister vessel, the Vachon, were assisting a fully loaded bulk carrier leaving the port at low tide. When the stern of the bulk carrier touched bottom, the aft tug  began pulling at maximum power. Shortly after, the tug's starboard fluid coupling high-temperature alarm sounded in the wheelhouse. The tug continued to pull at maximum power increasing the internal temperature of the coupling, melting the fusible plugs and releasing the oil into the machinery space. The hot oil vaporized and ignited when it made contact with a hot surface (either the engine exhaust manifold or by a spark that may have come from the nearby generator).

The TSB's post-occurrence examination of the Brochu revealed the following unsafe conditions that affected the crew's health and safety, and the tug's machinery operation, rendering it vulnerable to extensive damage in case of a coupling malfunction:

The on-going investigation has determined that at least 798 vessels worldwide may have similar arrangements.

The aforementioned is provided so that you may take whatever measures are considered appropriate in the circumstances. The TSB would appreciate being advised of any such action. Moreover, an investigator may follow up with you at a later date.

Original signed by

Marc-André Poisson
Investigations – Marine


Background information

Occurrence no.



Mr. Luc Charbonneau, Regional Senior Investigator, Engineering, Central Region

Mrs. Line Laroche, Regional Manager, Central Region