Failure of Snap Shackle

Report Text:

This is a large yacht where the rescue boat is stowed inside the hull via a shell door. The accident occurred during recovery of the rescue boat. Just as the rescue boat was being slewed into the tender bay, the port aft snap shackle of the lifting arrangement failed. The snap shackle attached the third leg of the lifting arrangement to the deck of the rescue boat. When this happened, the rescue boat swung downwards and to port, being held by the forward and starboard slings. Two deckhands had been seated in the rescue boat for hoisting and they fell into the water as the shackle failed. Each suffered minor injuries. Both wearing inflatable lifejackets remained conscious throughout and were recovered by other crew members. The cause was found to be failure of the snap shackle secured to the lifting point in the rescue boat. The yacht and its fittings were about 2 years old. The lifting gear was certificated for the load and had not been subjected to any severe loads since new. Regular inspections had been carried out as part of maintenance.

The lifting bridle snap shackles. Note that both the forward and port shackles have failed.

Fracture surfaces on port shackle. Note the corrosion especially in the bore of the holes for the pin.

CHIRP Comment:

The manager has subsequently sent us a report of a metallurgical investigation of the failure of the shackle. The report noted that there was corrosion present on the surface of the material that had fractured. The features on the fracture surface indicate that they failed by a fatigue mechanism, cracks initiating at the bore of the hole for the pin.

The manager advises that his company has replaced snap shackles in the lifting bridles of rescue boats with conventional shackles.

If you have experienced any failure with rescue boat equipment, please let us know.