Bundles and towed installation

Bundles and towed installation

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BOTTOM TOW

ƒ Bundle pulled along the seabed, usually with some buoyancy tanks attached ƒ Used in Gulf of Mexico, where lengths up to 16.1 km (10 miles) long have been installed ƒ Seabed must be flat with no obstructions ƒ Accurate surveying needed along whole route ƒ Any pipeline crossing must be protected

Tandem tugs

Bottom tow: The bundle is pulled along the seabed, usually with some buoyancy tanks attached, by one or more towing vessels This method has been primarily used in Gulf of Mexico There is a need for an accurately-surveyed tow corridor with no obstructions It is suitable for deep-water applications when a minimal bundle weight is required Crossing of third party pipelines can be a major problem Typical size of tugs might have a 250 tonnes to 300 tonnes (275 US tons to 330 US tons) bollard pull, towing in tandem at 8 knots (4.1 m/s). Perhaps two or three tugs may be required to overcome the seabed friction. It is unsafe to cross existing live gas lines using this method. Extensive mattress protection and ramps would be needed to lift the new line over. This approach does not have a good track record. In the Gulf of Mexico, there was a vertical step of rock some 3 m (10 ft) high, which had been missed by the survey team. During the tow-out, the front end of a pipeline was stopped by this feature but the back end continued under its own inertia. The pipeline was a complete write-off.

EXAMPLESOFBOTTOM-TOWFLOWLINEANDBUNDLEPROJECTS