A recent Safety Flash by the International Marine Contractors Association (IMCA), focuses on an incident, in which a crew member observed a piece of metal debris lying under the crane boom tip, during a vessel transit during which the crane was unused in its boom rest.
It was discovered that one of the three Crane Whip Line Block Catcher Limit Switches (3.6kg) had fallen off and had fallen 6.5m to the deck. There were no injuries.
What went wrong
- Inadequate design verification – the cross‐sectional area of the broken plate was not sufficient to bear the stress applied to the limit switch;
- The bolt spring was acting as a strong point and was creating unbalanced forces on the limit switch plate;
- There was insufficient preventive maintenance or inspection of this area.
What was the cause
- The equipment was not being used as it was originally designed;
- The maintenance schedule recommended by the crane manufacturer, was not adequate.
Lessons learned
- Testing of the limit switches during a third-party thorough examination, though providing satisfactory results, could prove misleading;
- Complicated access to the boom tip does not allow proper inspection of these and other integrated elements of this 900T crane.
Actions taken
- Work with the crane manufacturer on a new design of the limit switch plate;
- Amend preventive maintenance schedule and inspection program to include more frequent assessment;
- Look at other vessel cranes for any signs of potential weak points on the limit switches.
