The two winches, one port and one starboard are used to control towing of the paravanes which control the in-water spread of seismic acquisition equipment. Eight hydrophone streamer cables up to 8km long are towed from deck level using a special fibre rope over the vessel sides. Each of the winches has a 1.7m diameter, 200 mm wide cast brake drum, both of which had work hardened and scored. The hardness ruled out single point tooling and metal deposition and remachining was not an option due to the composition of the base material.
Once on board, the Metalock team set up one of their portable grinding units, supported on a special framework to ensure that the grinding machine and drum centrelines were on a common datum to assure optimum finish. The drum was revolved slowly using winch hydraulic drives. On completion of the first drum, the grinding set-up was moved to the second one for a repeat operation. 4mm of diameter on each drum was removed to clean up the surfaces over a period of, two days working round-the-clock with two two-man Metalock teams.
Whilst this work was progressing, Veritas fitted new thicker braking materials to the brake bands to compensate for the slightly smaller drum diameters and restore original clearances. When reassembled the winch brakes were checked and in the words of one of the Veritas engineers, “were as good as new”. The work had been carried out at a fraction of the cost of replacement and within the timeframe and budget allocated.