Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report Table 3.11: Tracked Cable Burial Machines 46 Type Burial Systems Available Maximum Burial Capability Eureka Jetting system Mechanical wheel cutter Mechanical chain excavator Otter Chain excavator for shallow water working Spencer Chain excavator for shallow water working 1.0m 1.2m 2.2m Maximum depth of Operation 2.2m Within diver operations 1.5m Within diver operations Operator 1500m Global Marine Global Marine Global Marine Nereus III Two separate burial tools available 1.0m 2500m Tyco Submarine Systems Ltd Nereus IV Two separate burial tools available 1.0m 2500m Tyco Submarine Systems Ltd CT2 Jet trenching system Up to 2.0m in sands and low to medium strength clays Trencher T2 Jetting system Mechanical chain excavator Trencher T1 Jetting system Mechanical chain excavator TM 03 Jetting system Mechanical wheel cutter Mechanical chain excavator TM 02 Jetting system Mechanical wheel cutter Mechanical chain excavator MED 1 Jetting system Mechanical chain excavator 1.6m 1.6m 2.0m 1.2m 1.0m 1.3m 2.3m 1.0m 1.2m 2.0m 1.0m 3.0m 3000m CTC Marine Projects Ltd Up to 1000m CTC Marine Projects Ltd Up to 1000m CTC Marine Projects Ltd Within diver operations Within diver operations Travocean Travocean 120m Travocean MED 1 Mechanical wheel cutter 1.5m 500m Travocean LBT1 Jetting system Mechanical wheel cutter Mechanical chain excavator 3.0m 1.2m 1.6m 50m Marine Projects Int. Tracked cable burial vehicles are usually operated (but not exclusively) in post laid burial mode to bury subsea cables which have been previously laid on the seabed and are typically used for shorter sections of cable burial. However, some vehicles have been used successfully to bury up to 10km lengths of subsea cable. Tracked cable burial vehicles are launched from the host vessel and then locate the subsea cable system to be buried by using a combination of cable detection and underwater camera systems. The tracks then straddle the subsea cable and the cable is loaded into the cable burial tool which is fitted to the vehicle. As the vehicle makes forward progression the vehicle has the capability to automatically steer along the line of the cable with an auto track capability linked to the cable locator system fitted to the front of the vehicle.
Cable types and installation techniques Divers are often required to assist in the loading and unloading of cable into and out of the cable burial tool fitted to the tracked vehicles. However, some of the vehicles have automatic cable loading and unloading features with an auto eject capability in the event of a power system failure to the tracked vehicle during operation. Cable owners are often reluctant to use such systems and therefore the more complex burial tools tend to be limited to shallow water use where diver intervention is possible. In deeper waters (which are out of diver range) only the more simple burial tools such as a jetting tool consisting of two forks which are positioned either side of the cable, tend to be used. There are three types of burial tools which are commonly fitted to tracked cable burial vehicles: ● ● ● Jetting systems (sometimes accompanied by a dedicated dredging system); Mechanical rock wheel cutters; and Mechanical chain excavator. These three types of burial tool are described below. Jetting systems Numerous types of jetting tools have been developed, most of which are subject to various patent protections, with operators usually favouring their own particular system. A jetting system works by fluidising the seabed using a combination of highflow, low pressure and low flow high pressure water jets to cut into sands, gravels and low to medium strength clays. Progress in clays is dictated by the available power budget to the tracked cable burial vehicle and the level of cohesion in the clay. In some cases a dredging system is employed to suck out the fluidised material to leave an open trench into which the cable then falls to the bottom through its self-weight. The jetting tools can also be fitted with a downwards forcing depressor which, together with the self-weight of the cable, helps to force the cable downwards in the fluidised trench. The effectiveness of any depressor system will be limited by the minimum bend radius and stiffness of the cable being buried and also by the on-bottom weight of the tracked cable vehicle itself to provide a downwards force onto the cable. This type of burial operation does give rise to sediments being suspended in the water adjacent to the burial operation and it can take a number of hours for such sediments to settle and for full visibility to return in the water column. Mechanical rock wheel cutters Mechanical rock wheel cutters can also be fitted to tracked cable burial vehicles and, as the name suggests, are used to cut narrow trenches into hard or rocky seabeds typically operating in the 1.5m trench depth range. The rock wheel 47
Page 1: REVIEW OF CABLING TECHNIQUES AND EN
Page 4 and 5: Review of Cabling Techniques and En
Page 9 and 10: Abbreviations AIS Automatic Identif
Page 11: TTS Temporary Threshold Shift TWA T
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Page 82 and 83: 4 Physical change 4.1 Introduction
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Review of Cabling Techniques and En
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6 Good practice measures This secti
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7 Gaps in understanding Research fo
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References Introduction Sinden, G.
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Appendix A: Standards and codes of
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Printed in UK on recycled paper. De
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