Rocks around the clock maintain schedule

MD Ian Hughes told MJ that HSSE’s diving teams are experienced and need to be, since the underwater procedures have to come off as pat as a drill-sergeant’s parade. ‘The pressure on them can be incredible, especially if you have the whole operation breathing down your neck and waiting for you to finish,’ he said, adding there is a sizeable cost implication to delays. HSSE’s dive crews have been using Holyhead Towing’s

Carmel Head

, a 15m fast twin waterjet powered aluminium support and transport vessel specifically designed for stable turbine access in 2m significant wave height, and Subocean’s 92m cable laying barge,

Discoverer

, which has just this year been kitted out afresh for its cable laying and wind farm roles.

The tides are very powerful around the towers so the dive teams only get a short window between the flow and ebb tides to do the work, says Mr Hughes. ‘They go in when the flow has lessened to 0.8 knots, and come out again when it has turned and is rising past the 0.7 knot mark in the other direction. Although at best this gives something over three hours, it can sometimes leave us as little as one hour to do the job.’ Planning, equipment and safety checks prevent much sitting around between dives.

The pressure was certainly on in one particular instance when the dive team had gone down to check the bottom of a J-tube, a trumpet-like section where the cable enters from the seabed. Unfortunately, investigation with an extended camera showed this was too impacted with mud for the array cable to be pulled through.

Work had to stop while the team laboriously moved the J-tube’s surrounding rock armour by hand, some 50 to 60 tons in all. These lumps of stone (weighing around 30 to 60 kg each) had to be picked up and put it into a basket hanging on the Discoverer’s crane, a delicate operation because divers and crane movements had to be kept clear of each other. Then the 12m trumpet had to be removed, cleaned and everything put back. In all, the operation took 12 divers, with six per shift working around the clock

Despite the difficulties, the operation was actually completed inside two days and the Discoverer got back to its cable laying schedule thanks to the dedication of the (now exhausted) dive teams.