Subsea Cables

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Caithness - Moray HVDC Link

The Caithness - Moray HVDC Link is a twin bundled High Voltage DC interconnector (single cable diameter 132mm) installed by ABB HV Cables (Sweden) AB (now NKT HV Cables AB) for Scottish Hydro Electric Transmission (SHE T) stretching approximately 113 km across the Moray Firth from Noss Head in Caithness to Portgordon in Moray.

During the period 15 February 2018 to 15 April 2018 (operations are very weather dependent), NKT will use the cable lay vessel (CLV) Victoria supported by the Multicat C-Fenna to complete the cable installation to shore at Portgordon. Operations will be carried out in the working area shown on the chart below.

The installation work at Portgordon will be carried out in a working area defined by the following coordinates: 

A - 57° 42.697' N

B - 57° 42.698' N

C - 57° 40.538' N

D - 57° 40.539' N

003° 01.906' W

003° 01.300' W

003° 01.551' W

003° 02.155' W

Operations will include the following:

1) Recovery & Relay of Wet Stored 'J Loop' (2 days)  Vessel:  CLV Victoria

The cable bundle which is to be installed in to the Portgordon landfall is currently laid in a temporary 'J loop' wet storage configuration between approximately kilometre point (KP) 5 and 2.5.  The cable bundle is stabilized with several rock bags. CLV Victoria will recover the rock bags and subsequently the wet stored cable starting from the temporarily laid cable end at KP5.  The cable bundle will be recovered back to approximately KP3.  On completion of recovery the cable bundle will be re-laid with the bundle separated into two, one DC cable and one bundled DC with fibre optic cable. The cables will be cut to length for jointing and the two ends deployed at approximately KP3.15 and KP3.4. 

2) Pull Out of Winch Wires Portgordon (1 day per Horizontal Directional Drilling (HDD) Duct)  Vessel:  Multicat C-Fenna

Three shore pull in winch wires will be hauled out through the HDD ducts prior to arrival of CLV Victoria at Portgordon.  This work will be done using a Multicat moored off the end of the HDDs at approximately KP1.6.  The Multicat will haul out the winch wires using previously installed messenger wires.  The pull out will be done using a winch on board the Multicat with the Multicat stationary in a four point mooring.  During pull out the HDDs will be lubricated internally using a pigging device.  Each point of the 4 point mooring is arranged with a 24te clump weight placed on the seabed by the Multicat itself. The Multicat will also place 6 off similar mooring points in planned positions extending out to approximately KP2.4.  All moorings are contained within the working area defined above. These will be used at a later stage. 

3) Float Out / Pull In of cable at Portgordon (1 day per HDD Duct)

Vessels:  CLV Victoria, Multicat C-Fenna, 4 x 7m workboats, 2 x 5.5m RIBs  and 1 x 14m workboat Coral Wind as MMO observer vessel / crew transfer vessel. The    workboats and RIBs will operate from Buckie Harbour. 

CLV Victoria will set up on the cable route at approx KP2.5. The Multicat will set up off the first HDD duct using the same mooring pattern as for pull out of the winch wires.  The end of the first cable will be connected to a towing line and towed by one of the 7m workboats toward the Multicat moored at the HDD duct / KP1.6.  As the cable is paid out from the CLV Victoria floats will be attached.  On reaching the Multicat the cable end will be connected to the winch wire previously installed in the HDD duct.  Hauling will commence from shore.  The cable will be drawn up and over the Multicat and through the HDD.  Cable floats will be removed at the Multicat and returned to the CLV Victoria.   A cable tensioner on the Multicat will be used to control the cable catenary entering the HDD duct subsea. On completion of the pull the Multicat will move along the cable toward the CLV Victoria removing floats and sinking the cable in to the pre-cut trench.  This work will be conducted with the Multicat winching itself between the 6 mooring points installed at the previous stage.  On reaching KP2.5 the cable with floats attached will be lifted overside. The Multicat will slip its moorings and clear away from the cable.  The CLV Victoria will then recover the short section with floats attached, remove floats and lay away placing the cable in the pre-cut trench.

4) Lay Down at Jointing Position (1/2 day per HDD) Vessel: CLV Victoria

On reaching the jointing position CLV Victoria will lay down the cable end in the configuration planned for jointing.  Steps 3 and 4 will be repeated for the remaining 2 cables.

5) Cable Jointing  (10 days)Vessel: CLV Victoria

On completion of operations 3 and 4 for all 3 cables, the CLV Victoria will recover the cable ends and set up for jointing.  During jointing the CLV Victoria will maintain a steady position and heading using DP.  On completion of jointing the cable joint and associated 'Omega' bight of cable will be laid on the seabed parallel with the main cable route.  Jointing will be performed at two locations.  Jointing is expected to take 5 days at each location making a total duration of 10 days.  Burial of the cable will be the subject of a future Notice to Mariners

Notice to Mariners: Caithness to Moray Backfill Operations

The Caithness - Moray HVDC Link is a twin bundled High Voltage DC interconnector installed by NKT HV Cables AB for Scottish Hydro Electric Transmission (SHEt) stretching approximately 113 km across the Moray Firth from Noss Head in Caithness to Portgordon in Moray.        

During the period 15 February 2018 to 30 April 2018 NKT will undertake the first of two backfill campaigns using the Siem Ruby and SCAR seabed system. Operations will take place at a number of locations between 58° 20.869' N 02° 43.234' W and 57° 59.391' N 02° 43.888' W along the Caithness - Moray Cable Route.

There is a working area 250m either side of the cable route centreline and other seafarers are requested to keep clear during these operations, guard vessels will be patrolling in the vicinity.

The second campaign is expected to commence in May 2018 and will be the subject of a future Notice to Mariners.

For further information: Richard Creed, ABB Tel: +44 7802 225532  email: Richard.creed@se.abb.com

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