Re-attaching the prefabricated midship section of the Skagerrak

Jumboising the Skagerrak

Cammell Laird jumboises Nexans' cablelayer Skagerrak.

Many a company executive has felt dwarfed by the events surrounding him, and many has seen fit to echo the words of Chief Brody from the 1975 movie Jaws: 'We're going to need a bigger boat...'. These words, however, couldn't have rung truer than in the board room

of Nexans. The company recently found itself obliged to extend its subsea cable laying capabilities. Its choice, though, was not to source itself a new vessel, but to take a much more hands-on approach. That is

why, at Cammell Laird Shiprepairers and Shipbuilders dockyard in Birkenhead, an £8m, two-month, fast-track conversion was carried out on the company's existing ship the Skagerrak.

The conversion and upgrade has increased the Skagerrak's capability to carry out even larger-scale power cable and umbilical installation projects, to meet the changing needs of customers in the subsea interconnector and oil and gas sectors. It has also extended its service life and increased its autonomy while at sea.

The major element in the project has been the insertion of a new 12.5m pre-fabricated hull section that has increased the ship's overall length to 112.25m. An additional accommodation module has also been installed, taking the total number of single cabins on board to 60, together with a new work deck, complete with cable-handling equipment, that has increased the on-deck storage capacity to around 2,000m2 (from 900m2). The upgrade has also increased the ship's deadweight from 7,886t to 9,373t.

'Owning and operating our own dedicated cable ship forms a vital part of Nexans' strategy to provide a comprehensive service for subsea projects, from design, development and manufacture to installation,' says Krister Granlie, managing director of Nexans' Umbilicals & Submarine High Voltage Business Group. 'This major upgrade and conversion of the Skagerrak underlines our commitment to the subsea sector, and ensures we are well prepared to handle the growing market trend for ever longer cables and larger scale installations.'

Cammell Laird's managing director Linton Roberts says the yard 'pulled out all the stops' to complete the multi-million pound fast-track conversion and upgrade contract.

He explains: 'Our business specialisation is commercial military repair, refit, conversion and heavy module fabrication in support of offshore oil and gas, renewables markets and a lot of land based projects. We drydock around 100 vessels per annum for refit and repair and many more dealt with afloat. Around 80 per cent of our work is repeat business, so the type of company we like to partner with on projects like this is companies like Nexans, who like to develop a very close relationship with their customers.

'Current major opportunities we are pursuing - or we have already won - obviously include the Skagerrak, which we see as a very important breakthrough into the Norwegian market. We would like to do more business here in terms of conversion, but we already do a lot of oil and gas conversions, generally to vessels. The yard has also recently been awarded the contract to build 6,000t of steel in support of the Queen Elizabeth-class aircraft carriers for the Royal Navy.'

Skagerrak conversion

The conversion of the Skagerrak was a rapid project as the contract was only awarded in early September 2009, and Cammell Laird had some 800t of steel to prefabricate before the vessel arrived. The vessel dry-docked at the end of January 2010, and the delivery was completed on schedule for April. The main scope of work was the mid-ship section of some 500 tonnes, which also includes a 100 tonne plus accommodation block on top of the mid-ship section. 'This takes advantage of the extra deadweight that we have developed,' explains Roberts.

Nexans decided to increase the crew facilities with the addition of 18 en suite cabins in the new accommodation module. 'Another big advantage with having that extra deadweight is an additional very large working deck area that sits on top of the unit and includes cable repair equipment and maintenance equipment,' says Roberts. 'Another aspect is that the turntable is now some 12.5m further away from the cable laying equipment, so there was a considerable amount of fabrication work to deliver the cable to the aft of the ship.'

It is a very complex conversion as there is a lot of ancillary work associated with delivering the ship to modern standards which you don't see, such as subdivisions in the depths of the ship to give it modern damage stability criteria.

The forward accommodation was upgraded to increase the living facilities for contractors onboard. 'We have also put a brand new sewage system in the ship with a 2010-compliant sewage treatment plant, and have brought the system onto a vacuum system from the existing accommodation forward,' says Roberts.

As the crew capacity has increased the lifesaving appliances have also had to be increased, including new lifeboats and new liferafts. A number of large cranes have also been fitted to support the cable-laying and subsea construction activities.

'The key project challenge for us was minimising the vessels down-time, which was central to the project success for Nexans, as the vessel is one of their primary assets for laying submarine cables, so we had to create solutions to maximise prefabrication work and minimise time in the shipyard,' states Roberts. 'Whilst in new units this it is quite easy to do, in the systems which we fitted to the ship it was a little bit more complex in terms of prefabricated pipes, and bulkheads, which had to be fitted in situ.' The yard also had to facilitate the prefabrication of the largest units possible to maximise any pre-outfitting opportunities to minimise work in the dry-dock.

'We had to engineer a dry lifting using the largest unit we could lift and a moving arrangement for about 750t of pre-fabricated steel because we didn't want to waste any time floating the ship out of the dry-dock and floating the new section in,' he says. 'We also had to integrate the new structure to the old with the minimum amount of rework and integrate the new systems to the old and upgrade the systems to extend the vessel's life.'

Midship lift

The new mid-ship section was around 500t when it came out of the construction hall. The section was built completely under cover with a high level of outfit. The tanks were painted, ladders, manholes and the heads all installed, as was all the vessel's structure, ballast lines, fuel lines, bilge lines and all pipework pre-installed, which was a key part of the project.

'Four days after the vessel arrived it was in two halves,' he explains. 'The ship was cut and driven apart. The forward end of the ship weighed some 4,000t, so we used transporters and an innovative docking arrangement so we could actually dock the ship, then pick it up and put it on a different docking arrangement. The most pleasing thing for the shipyard is the engineering concepts transferring to the reality.'

There was a considerable amount of planning that went into the actual cut and shut, something that is only legal when it comes to ships. The fifth day the mid-body was lifted. 'We had moved the mid-body section in two days before the vessel arrived, built the crane behind it, and we lifted it dry,' says Roberts. 'Because of the radius of the dock, which is some 45m wide, we lifted it down the side wall of the drydock and split the ship a bit further apart than we needed to in order to rotate it 90 degrees. Therefore we could maximise the lifting capacity of the crane.

'If we had tried to lift it to the centre of the dry-dock we couldn't have done as big a unit and obviously building the unit was the critical thing for us.'

On the same day the accommodation module was lifted down it was fixed to the mid-ship section so that when the unit was moved to the centre of the dock it was the full weight of the unit.

Day six saw the mid-body and the existing hull combining. 'Whilst we followed the ships drawings and we sent teams to see the ship, we couldn't swim underwater, so the ships drawings were surprisingly accurate and the fit was very good.'

The Skagerrak is now back in action with its increased capacity to lay undersea cables and umbilicals and its improved accommodation and facilities which will allow the ship to stay at sea longer.

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