Page 86: of Offshore Engineer Magazine (May/Jun 2015)

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Subsea

Launching the Fugro Q1400 trenching system. Photos from Fugro Subsea.

narrow relative to its depth, will nor- mally partially collapse back.

The vessel deck transfer system has been developed by Fugro and SMD to enable the trenching team to change between cutting and jetting modes. The cutting or jetting skids are switched via a fxed pallet attached to preinstalled skid- ding beams, which allows changes to be made while at sea, without a crane, and

All terrain in under 18 hours. The Q1400 launch and recovery system (LARS) uses an A of this is delivered through variable frame equipped with cross beam winches speed drive electric motors to direct- and cursor. The LARS is certifed by trenching drive water pumps. The jetting tool has Lloyds to sea state 6, allowing twin-legged parallel jet swords and can operations to continue even in a trench up to 3m deep in soil conditions for trenching. Conventional systems are heavy swell up to 3m signifcant

Subsea trenching has become from 5-100kPa using 2m or 3m jetting deployed from separate vessels, using wave height.

more versatile with Fugro and

Once deployed, the trencher’s water jetting for loose granular soils and swords, with the Q1400 system capable tracks are used to run it along the chain cutting for hard clay and boulders. of accommodating pipelines, cables and

SMD’s Q1400. Mike Daniel seabed for both jetting and cutting

Fugro collaborated with Soil Machine umbilicals up to 900mm in diameter. explains. operations. Thrusters can be used

Dynamics (SMD) over the design of an With pre-laid rigid pipe the trenching for adjusting its position, lifting the innovative, all-purpose trenching system. jet legs fuidize the soil on either side of t is important to bury wind farm The Q1400 provided interchangeable the pipe causing it to sink into the sea- trencher off the seabed to aid move- cables, oil umbilicals and pipelines to water jet and chain cutting skids, which bed. For trenching pre-laid fexible pipes ment in very soft soil; they can also

I protect them from damage, particu- can be exchanged onboard the vessel the Q1400 uses a 150hp, 2m x 400mm be used to hop along the seabed.

chain cutter and two loading arms, which while at sea. larly in the crowded, relatively shallow The Fugro Saltire has been can take fexibles, cables and umbilicals The Q1400 trenching system can waters off European coasts. adapted to take the Q1400 and up to 250mm diameter. perform jet trenching in soils of up to A 2009 report by the International operates as a dedicated trenching

Backflling can take place at the same 100kPa shear strength, i.e. sands and Cable Protection Committee suggests support vessel. The trencher is time as jetting. Separate water pump softer clays. For medium and harder two-thirds of all telecommunication cable normally operated in conjunction clays up to 500kPa, the mechanical chain systems can either backfll or keep the breaks are caused by ships’ anchors and with a Fugro work class FCV 3000 trench open depending on the cli- cutter is used. Jetting speeds are usually commercial fshing trawlers. Unburied ROV for pre- and post-trenching ent’s needs. The method of backflling 300-500m/hr, but with chain cutting that cables and pipelines present a serious surveys, as well as route clearance depends on the soil type. With chain falls to 100-200m/hr. The Q1400 can hazard for trawlers which can lose gear if debris is found along the cable cutting it backflls naturally, because as operate in 10-3000m water depth. or even be pulled under. paths. Fugro’s second trencher, the umbilical or cable is trenched with In jet trenching mode, the Q1400 has a Seabed geology varies widely and two based in Montrose in Scotland, the chain cutter the trench, which is very total available power of 1459hp - 1000hp types of tractor based system are used can be deployed for projects as

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