Failure to calibrate MRU led to near-miss
- Safety Flash
- Published on 15 December 2010
- Generated on 17 November 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.
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