As UK MAIB reports in its most recent Safety Digest, a cruise ship’s engineering team were working with the engine manufacturer’s technicians to overhaul a large diesel generator, using the engine room’s overhead gantry crane to lift the heavy engine components.
The incident
One of the 1200kg cylinder liners was being lifted into position above the engine, a process that required the electric winch motor to raise the crane hook to its maximum lift height, when the crane’s hoisting wire suddenly snapped.
The suspended cylinder liner fell onto the engine, causing damage to both pieces of equipment, and struck the left foot of an engine room fitter who was standing nearby. The crew member was treated in hospital for a broken toe and subsequently repatriated. The failed hoisting wire had been renewed shortly before the engine maintenance work started but was 7m shorter than the wire length specified by the crane manufacturer in its technical manual.
The shorter length wire affected the operation of the crane’s hoist limit switch and prevented it from cutting power to the winch electric motor when the hook was raised to the maximum lift height; the winch motor was therefore able to overload the wire and cause it to fail.
Tests of the three remaining engine room cranes established that all of the limit switches failed to stop power to the winch motors and thus failed to meet manufacturer requirements. The wire length recorded in the ship’s planned maintenance system (PMS) computer was found to be incorrect when compared with the manufacturer’s specification.
The cranes were taken out of service for repair and the ship’s engineering team were instructed to conduct a full inspection of engine room hoisting devices and take necessary steps to ensure that all equipment met manufacturer specifications. They were also reminded to test the hoist limit switches before operating the cranes.
Lessons learned
- Hazard: The crew member was lucky on this occasion but the first lesson here is to not stand under or near to suspended loads, regardless of whether the lifting equipment is new or has been recently overhauled. This incident is a reminder that equipment failure can occur at any time, potentially with severe consequences.
- Margin of safety: It is unclear why the wire length documented in the PMS was incorrect. However, overreliance on hoist limit switches to cut power to the winch electric motor is risky, whether on cranes or lifeboat davits. A high torque electric winch motor has the potential to over-stress the hoist wire, causing it to fail. It is always safer to stop the lifting operation before overhead capacity is reached, even if the system is correctly set up and the limit switch has been tested.
- Risk: Lifting operations are hazardous and require careful risk assessment to prevent accidents. Chapter 19 of the Code of Safe Working Practices for Merchant Seafarers (COSWP) provides invaluable guidance on what control measures to take before and during such tasks.
