Trenching System is a cost effective and efficient solution to subsea tasks: Boulder Clearing / Seabed Preparation; Trenching – Pre-Cut, Post-Lay, Multipass, Cable Lay; Burial. This system can be mobilised on one tow vessel, deployed over the stern roller, negating the need for an A-Frame or crane.
This system can complete the entire trenching Scope of Work using one contractor in one mobilisation, allowing for a great reduction in risk, costs and improvements in time efficiency.
Trenching of pipelines
To protect an installed pipeline on the seabed, for example from damage by the trawler boards of fishing boats, currents or other forces, many pipelines in water depths up to 450 m (1,480 ft) are trenched. Mechanical trencher digs a V-shaped trench underneath the pipe, into which the pipe gradually sinks behind the machine.
Mechanical trencher is capable of mechanically trenching pipelines with an outer diameter of up to 42″ and pipelines of up to 48″ in a wide range of soils. It can also perform other operations such as, backfilling, free span corrections and exposing buried objects.
Backfill
When configured in Backfill mode, the plough is used to return the spoil to the trench burying the pipeline or cable. The mouldboards are adjustable to allow varying degrees of spoil to pass through the plough in order to achieve the desired burial depth. The plough in Backfill mode is a configuration of the Boulder clearance plough, which is ideal for reducing the costs of mobilization, allowing complete trenching scopes of work to be complete with just a single mobilization.
Procedure
Survey route for backfill in preparation
Set backfill plough to provide the correct level of backfill
Launch plough off stern roller of tow vessel
Align plough with start of backfill pass
Begin tow and monitor with the ROV to ensure the plough is following the determined route and checking integrity of the backfill
Once pass is complete, review and repeat if necessary
Recover plough to vessel
