Bundles and towed installation

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Bundles and towed installation

BALLAST CHAINS

Near-neutrally buoyant bundle for towout (flooded annulus once field is reached)

8 m to 10 m (26 ft to 33 ft)

Webbing strap

2 m to 3 m (6 to 10 ft) of 76 mm (3 in) scrap chain

Carrier sits ~5 m (16 ft) above seabed during trim

Fuse wire

Odd N° of links of chain

‘Extra’ links on seabed for stability to bundle during trimming for tow and at field location

Bundle design – ballast chains Centres are determined so as to provide neutral buoyancy of the bundle and pullhead assembly in the sea prior to and during the tow (adjustment made by divers using trimming links) A target net downward force on the sea bed of approximately 30 N/m (2 lb/ft) is achieved Stud link anchor chains are typically strung at between 8 m and 10 m (26 ft to 33 ft) centres. They normally have an odd number of links to help stability during tow. Every fifth or seventh chain has the fuse wire and three additional links.

TOWINGCONFIGURATION

TOWING CONFIGURATION

ƒ Controlled-depth tow (CDT) ƒ Also known as mid-depth tow ƒ Powerful tugs control depth of towheads

Up to 7½ km (5 miles) long

Trail tug

Tow tug

Transponders

Trailhead

Towhead

Ballast chains

Hydrodynamic lift on ballast chains causing bundle to rise in water column.