Feature 4 | SUBSEA SUPPORT VESSELS


the plough method is impractical; you would probably have to come back and check the trench and cable position anyway, incurring more time and costs. “When the mechanical arm of the plough


is combined with the plough cable, product cable and various umbilicals, things can become complex. Te ITAT 800 will feature just one umbilical, linked to the controlling support vessel.” Naturally, the elimination of a complex


jungle of cables is intended to reduce the likelihood of an accident, although the most obvious advantage of discarding the ploughing method – namely, the removal of a heavy, sharp metal object from the vicinity of the power cable – speaks for itself.


Heavy duty At time of writing, Pharos Offshore was in discussions with builders, and the group hopes to be able to unveil the new ROV in 2012. Designed to feature a relatively car-sized length of 1m, a width of 4.3m and a height of 2.4m, the ITAT 800’s bulky nature is necessitated by the task it will be undertaking. McDougall says: “A lot of existing


trencher technology is mainly used to install fibre-optic cabling, for telecommunications companies, which is a lot lighter than the power cables required for offshore wind farms – most trencher ROVs out there aren’t big enough, nor boast the ability, to handle power cable laying of this nature.


“The typical trencher ROV generates


about 200-300hp [147-220kW] output, whereas we’re boosting the ITAT 800’s output to 800hp [588kW].” According to the design specifications, the ITAT 800 should be able to descend to maximum depths of 250m, which McDougall believes will grant the machine the capability to handle an unlimited amount of wind farms, particularly as the average depth for many of the European farms has been recorded at approximately 40m. Te subsea operator will control the ITAT


800 from his support vessel on the surface; McDougall estimates that this vessel would contain six operators, each taking turns on a 24-hour watch, with a seventh member of crew acting as supervisor. Te ROV will feature cameras and sonar capabilities, meaning that if operations are conducted in turbulent waters, or conditions of reduced visibility, the ITAT 800 can still be guided along its allocated route. Upon completion next year, the unit will


be housed in an A-Frame, also featuring three or four containers packed with the housing control system, spare parts and various other electronic control modules, and this design is intended to facilitate the movement of the ROV and its components from ship to ship.


Jet power Lacking a plough-style device to cut into the seabed soil, the ITAT 800 will use a process dubbed ‘fluidisation’ to construct


Rise of the robots


Te offshore sector is playing host to an upturn in ROV activity, estimated to increase by 43% over the next four years.


with a greater number of opportunities for unit deployment, analysts opine. An international study hosted by the International Marine Contractors Association (IMCA) showed increased ROV activity over the course of 2010; focusing on two days in February and August last year, IMCA found that a total


A 26


predicted upswing in offshore construction and drilling activity could provide the ROV sector


of 3185 superintendents, supervisors, pilot technicians and offshore ROV support personnel were working with 528 vehicles in the former month, while, by August, this total had increased to 3408 members of personnel and 577 vehicles. “Since the figures represent a snapshot,


they do not take into account any major contract that may have been completed shortly before the days of the count, nor one which may have started shortly after,”


comments Hugh Williams, IMCA chief executive. He adds that the figures for ROV personnel indicate a slight decrease on 2009’s figures, although the number of actual vehicles in operation was higher than the previous year’s tally. Similarly, analyst Infield Systems notes


a bounce back this year from what it describes as being a relative dip in ROV activity spanning 2009-2010, when the first ill effects of the financial downturn kicked


Offshore Marine Technology 4th Quarter 2011


trenches for the offshore wind farm cables. Tis comprises a water jetting technology, with interchangeable nozzles, which literally cuts into the seabed, typically at a pressure of 16bar. Te process of pumping so much high-pressure water into the soil turns the designated soil area into slurry, into which the power cable can be laid, before current fills the trench back in. Although this a preferable methodology


for plough trenching when operating in offshore wind farm arrays, it is important that operators realise it does have its limits; the soil can sometimes prove so hard that water jetting alone will not work, especially when rocks are present. When utilising the fluidisation process,


Pharos Offshore estimates that customers will be able to position interconnecting wind farm power cables at depths of up to 3m below the seabed. Te ITAT 800 will be constructed from


a variety of readily available, off-the-shelf components – including its pumps, motors and cameras, for example – in order to provide flexibility to users and aid them in obtaining back-up parts, McDougall says. Te hydraulic tracks for the unit have been modified from a product originally used by the logging industry, which have been marinised for deep sea handling. Following delivery next year, the group expects to sell and lease the ROV to clients working on both UK Round 3 wind farm projects and forthcoming US turbine farm developments. OMT


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