An offshore support vessel operator asked us to check and restore the towing equipment on one of its vessels at Dubai Maritime City. After a full health check, we rebuilt the shark jaw, towing pin, lifter and winch brake cylinders, serviced the power packs and renewed the hoses across the towing system.
The problem
Shark jaws and towing pins hold and guide the tow wire at the stern. They work in seawater, take shock loads and are often left idle between jobs, so corrosion and seal wear build up unseen. The operator wanted the whole system checked and brought back to a reliable state, not just the item that was leaking.
What we found
We started with a pre-inspection of the tow winch, towing pins and shark jaws: functional and safety checks, a muster of onboard spares and documents, and a written report with recommended work. Strip-down then showed:
- Shark jaw cylinders, port and starboard: piston rods beyond repair, worn swivel bearings, pins and seamless tubing
- Towing pin cylinders: the port piston rod beyond repair, worn bushes and pins on both sides
- Lifter cylinder: barrel and end bracket beyond repair
- Anchor-handling winch brake cylinder: a damaged piston rod and worn threads on the gland nut and barrel
- Towing winch brake cylinder: worn seals
- Power packs: aged oil, accumulators low on nitrogen and worn motor-pump coupling spiders
- Capstans: worn speed control valves, a directional valve needing overhaul and hoses due for renewal
What we did
- Overhauled and tested the shark jaw, towing pin and lifter pin cylinders and both winch brake cylinders. New piston rods were made to sample for both shark jaws, the port towing pin and the anchor-handling winch brake cylinder. A new barrel with end bracket was made for the lifter cylinder. Gland nut and barrel threads were reworked, and bearings, bushes, pins and tubes renewed.
- On the towing winch power pack, renewed the oil, recharged three accumulators with nitrogen and renewed two pressure gauges.
- Renewed two motor-pump coupling spiders, and reassembled and function tested the towing pin power pack pump.
- Overhauled both capstan speed control valves, the starboard capstan directional valve, and renewed the speed change valve, ball valves and gauges.
- Renewed 18 hoses with adaptors on the towing system and 7 on each capstan.
- Fitted a new pressure transducer and renewed two steering system ball valves.
Result
Seven cylinders were rebuilt and tested, three accumulators recharged and 32 hoses renewed, leaving the towing system in a known condition with a report the operator could file with its maintenance records. The work ran in stages over several weeks to fit the vessel’s programme, with removal and refit of some cylinders done by the crew.
