Skip to content

Near miss: uncontrolled movement of mooring chain

What happened

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.


What went wrong?  

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.

Causal factors

  • 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.

Additionally, it was noted that there were no physical barriers in place for working around equipment.

What lessons were learnt?

  • 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.

Members may wish to refer to:

Safety Event

Published: 19 January 2021
Download: IMCA SF 03/21

IMCA Safety Flashes
Submit a Report

IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of all. The effectiveness of the IMCA Safety Flash system depends on Members sharing information and so avoiding repeat incidents. Please consider adding [email protected] to your internal distribution list for safety alerts or manually submitting information on incidents you consider may be relevant. All information is anonymised or sanitised, as appropriate.

IMCA’s store terms and conditions ( apply to all downloads from IMCA’s website, including this document.

IMCA makes every effort to ensure the accuracy and reliability of the data contained in the documents it publishes, but IMCA shall not be liable for any guidance and/or recommendation and/or statement herein contained. The information contained in this document does not fulfil or replace any individual’s or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.