Bundles and towed installation

30

Bundles and towed installation

EXAMPLES OF BOTTOM-TOW FLOWLINE AND BUNDLE PROJECTS

Flowline and control installed beneath ice Multiple bundled lines Multiple bundled lines

1,000 m (3,180ft)

55 m (381 ft)

Panarctic 1977 Drake 76

730 m (2,400 ft) 470 m (1,550 ft) 840 m (2,750 ft) 1,350 m (4,430 ft)

Placid 1986 Green Canyon 16,100 m (52,820 ft)

9,660 m (31,700 ft) 11,300 m (36,980 ft) 2,900 m (9,510 ft)

Enserch 1992 Mississippi Canyon 441

Twin P-in-P flowlines

BP

1997 Troika

Twin flowlines in insulated carrier

Total

2001 Girassol

This table includes examples of bundles and flowlines installed by the bottom-tow method. This is not a comprehensive list but includes some notable examples including the longest installed length by this method of 16.1 km (10 miles).

OFF-BOTTOMORNEAR-BOTTOMTOW

OFF-BOTTOM OR NEAR-BOTTOM TOW

ƒ Suitable when the seabed is relatively even and there are only a few crossings required ƒ Reduction in tow forces ƒ Accommodates unevenness of seabed

Single tug

Buoyancy with chain ballast

Transponder

Simple towhead structure

Off-bottom tow: The bundle is 2 m to 3 m (6 ft to 10 ft) clear of the seabed with ballast chains maintaining contact with the seabed; It is suitable when the seabed is relatively even and there are only a few crossings required; Towing is by one or two vessels. A trail tug (not shown) is only required for final positioning; It results in a slower installation than controlled-depth tow (CDT) and the bundle is usually designed to be heavier to provide stability;