Ensure that the safe working load, SWL, of a capstan is greater than the rated pull of the capstan, says a safety alert from the International Marine Contractors Association, IMCA, following an incident aboard one of its members’ vessels. If the capstan does not stall before the wire fails the resulting parting of the wires can cause horrifying injuries.
Due to the company’s clear deck policy nobody was at risk but similar policies may not be in force, or practical, under other circumstances.
Says the IMCA:
“A member has reported an incident in which a wire parted whilst dragging an anchor buoy on deck. The incident occurred when a vessel was involved in a Delta Flipper anchor drag test operation. The operation consisted of deployment one after the other, of an anchor buoy and a Delta Flipper type anchor, using two capstan wires, and then recovery back to deck using the main tow wire. Three tests were carried out successfully. During the fourth test, the port side capstan wire parted whilst dragging the anchor buoy on deck. There were no injuries.”
An investigation revealed the following factors:
- The certified safe working load (SWL) of the capstan wire was below the rated pull;
- Tear and wear – friction of capstan wire rope on the edging of capstan flanges;
- There had been no visual checks for tear and wear of wires made by the crew after each anchor drag test;
- Another, more preferable and safer, option of using tugger winches had not been considered for this operation.
The following lessons can be learnt:
- SWL requirements should always be considered when rigging/towing operations on deck. Ensure that the capstans rated pull is below the certified SWL of the capstan wire. The capstan should stall before the wire fails;
- Anchors should be moved on deck only with tugger wires connected either through towing pins or snatch blocks fixed on the pad eyes next to the stern roller, ensuring that all pinch points for the wires are identified and avoided;
- Capstan winches should not be used as a substitute for a deck tugger;
- When using capstans, care should be taken with wire lead in and lead out angles to avoid wire abrasion from the capstan flanges;
- Avoid excessive wraps on the capstan drum which would cause knifing damage of the wire and subsequently reduce the wire SWL;