201862 Inspection failure precedes link failure
Inspection failure precedes link failure
As edited from the Bahamas Maritime Authority Safety Alert 17-07
A tender boat on a passenger ship fell from its stowed position into the water, without warning and without any intervention by the crew. No one was injured, but the tender itself was a total loss.
The fall was caused by the catastrophic failure of the link that connects the fall block to the release gear hook. The investigation found that, among other things, the actual measured safety factor of the link was less than 5:1. This was well below the required minimum safety factor of 6:1 as specified by the LSA Code. Notwithstanding this less than adequate condition, the immediate cause of the failure was found to be a fatigue fracture.
The initiation of the fracture was attributed to the location of the stainless steel handle which was attached to the straight part of the link. The likely mechanism for the fracture was either corrosion fatigue (galvanic corrosion) or fatigue initiated from a minor indent at the surface.
Lessons learned
- Non-destructive testing should be carried out regularly to verify the condition of gear such as links.
- Items such as bolted-on handles should be removed to ensure links can be given a full visual inspection.
- During inspections the dimensions of the connecting links should be measured to ascertain whether there has been any reduction in diameter as a result of corrosion.
- When possible, avoid connecting two metal parts that have different galvanic (sea water environment) values.