Failure to calibrate MRU led to near-miss
- Safety Flash
- Published on 15 December 2010
- Generated on 10 July 2025
- IMCA SF 08/10
- 2 minute read
A Member has reported an incident in which a vessel crane made an uncontrolled payout of approximately 27 metres of winch wire.
What happened?
During crane operations to relocate an anode skid the winch began paying out for no apparen’t reason. The payout occurred when changeover was taking place between auto-tension and active heave modes. This should have allowed the crane to lift the skid in a controlled manner. There were no injuries or damage to assets, but the incident was classified as a high potential near miss.
Our Member’s investigation revealed the following:
The motion reference unit (MRU) housed within the crane had not been calibrated since it was installed in 2008. This had led to incorrect readings from the crane computer system. The calibration had been omitted owing to a changeover in companies responsible for the MRU and a lapse in the onboard planned maintenance system.
The MRU was landed for calibration and it was noted that there was a relatively high offset on the heave signal from the MRU. The decision was then taken to change out the MRU for a calibrated spare.
Our Member took the following actions:
Following this incident our member decided to carry out a gap analysis of the planned maintenance system of the crane and all other major components in safety critical equipment onboard the vessel against the possibility of similar lapses.
IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of the entire offshore industry.
The effectiveness of the IMCA Safety Flash system depends on the industry sharing information and so avoiding repeat incidents. Incidents are classified according to IOGP's Life Saving Rules.
All information is anonymised or sanitised, as appropriate, and warnings for graphic content included where possible.
IMCA makes every effort to ensure both the accuracy and reliability of the information shared, but is 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.
Share your safety incidents with IMCA online. Sign-up to receive Safety Flashes straight to your email.