The incident

There was a sudden and uncontrolled movement of very heavy mooring chain during chain laying operations. A vessel was laying a 170mm diameter bottom chain from a suction anchor towards an FPSO.

When the chain end was approaching, the shark jaw was engaged onto the chain to remove tension, in order to enable handling of the chain end from its chain locker.

The last few chain links of the bottom chain then moved uncontrolled over the chain handling unit and rolled/dropped on deck, under its own weight, in between the chain lifter and the winch hangar.

The bosun was located close to where the chain dropped and moved away when he noticed the uncontrolled chain movement starting.

According to IMCA:

The circulation pump on the chain handling unit tripped, causing the chain lifter to loose its holding force, and hence the chain catenary forward of the unit pulled the tail end over.


  • This was a new vessel with as yet, a lack of full implementation of required safety systems.
  • There was insufficient job safety preparation and risk management in place.
  • There was inadequate understanding of the failure modes for the system.
  • The vessel’s generic procedures & job safety analyses were not re-visited with respect to project-specific loads and factors.
  • The chain handling unit was not included in the vessel anchor handling and tow manual.
  • There were no physical barriers in place for working around equipment.

Lessons learned:

  • Implement additional physical barriers on deck.
  • Update vessel documentation including SJA’s and manuals.
  • Assess need for additional technical barriers on chain handling unit and circulation pump (including upscaling of pump and set-up on alarm).
  • Formalise training and familiarisation.