Lessons Learned: Twisted chains on fishing vessels

In its latest Safety Digest, UK MAIB describes a case of serious injuries onboard a fishing vessel, while the fishermen were stowing the gear. The incident was caused by the failure of a length of chain from which the block was suspended.

The incident

The crew of a beam trawler had completed their last haul for the trip and were stowing the gear. The port tow beam was raised and tensioned using dedicated chains. Three crewmen climbed onto the conveyor belt and put a strop around the net to bring it on board. Two of them had just stepped off the conveyor onto the deck when the entire gear, comprising the tow beam, bridle chains and pulley block collapsed onto the conveyor and deck.

One of the crewmen on deck suffered a broken shoulder; the crewman who was still on the conveyor belt suffered injuries to his head and multiple fractures to one of his hands. Most of the injuries were caused by the bridle chains. It was fortunate that no one was struck by the tow beam or pulley block.

Probable Cause

According to MAIB, the accident was caused by the failure of a length of chain from which the block was suspended. One end of the chain was attached to a quick release wire and the other end was looped through the block and fastened onto itself with a hammerlock link.

However, the two chain links joined by the hammerlock were not in the same plane, forcing them together under load, causing a twisting force. The starboard side chain had been linked without introducing such a twist and showed no signs of failure.

Lessons Learned

1. Chains must not be twisted in operation. Twisted chains will fail at a significantly lower load than those that are not.
2. It is not good practice to loop chain around blocks as this will introduce additional loads on the chain links. If it cannot be avoided, the diameter of the block should be more than seven times the diameter of the chain link.
3. Avoid standing directly under loaded gear. Personal protective equipment must always be worn, but it cannot be expected to protect you fully if heavy gear falls on you.