Page 149 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

Any increase in the size of the topside equipment can have a dramatic effect on the support platform requirements. As the offshore ROV service companies contemplate taking their operations even deeper offshore, the size of the umbilical, tether, winch, power system, vehicle, spares, control van, and launch system will all grow. There will be a point, possibly as near as 4000 m, where the heavily armored steel umbilicals will become too heavy to support their own weight much less the TMS and vehicle on the other end. This fact supports the arguments by the all-electric vehicle manufacturers that their systems (which are typically simpler, more efficient, and thus lighter) will be able to support future deep operations more efficiently than the heavy hydraulically powered work vehicles.
Hydraulic vehicle aficionados will argue that they will be able to use a lighter nonmetallic umbilical. Such umbilicals are made of Kevlar and used by most 20,000 ft (6000 m) depth-rated ROVs. This solves the suspension weight problem, albeit at a higher cost for the umbilical. However, the synthetic fiber materials used in such umbilicals may not withstand the wear and tear experienced during the years of service expected of them in the oil field. The steel-armored cables of today’s systems have been proven to be a cost-effective solution.
It will also be argued that today’s manipulators and tools require hydraulic power (which is, at this time, very true for the heavy-duty systems). There are some smaller all-electric manipulators on the market, but the size and construction (and thus the strength-to-weight ratio) of electric manipulators cannot yet match their hydraulic counterparts developed for the offshore market. Just as today’s electric vehicles are leveraging the advancements in elec- tronics and electric drive technology, manipulator manufacturers are keeping an eye on any advancements that would allow the development of a comparable electric underwater manipulator.
However, for the time being, the all-electric vehicle manufacturers will continue to supply eas- ily integrated skid packages that can provide auxiliary hydraulic power, manipulators, and tools as necessary without modifying their basic ROV system.
So, who wins the debate? Neither side, actually. Because the electric, hydraulic, and electro- hydraulic vehicles all have their niche within the market (at this time), both types of vehicles will continue to proliferate. Table 6.2 provides a cross section of the size and capability of all three vehicle types. As can be seen, once a vehicle is big enough for a heavy-duty hydraulic system, then that is the class of system on which the manufacturers tend to concentrate. But do not dis- count the all-electric vehicles when manufacturers such as Seaeye and Sub-Atlantic are marketing 20,000 ft (6000 m) work vehicles. A relatively new player on the block, Elsub Technologies in Norway, is touting their 200 hp all-electric vehicle that carries an auxiliary hydraulic package for manipulator and tooling operations.
Oceaneering had also developed an all-electric vehicle—the E-Magnum. Unfortunately, after 7- plus years of reliable operation, it was lost with the Deepwater Horizon catastrophe. They are now looking at designs for use in the Arctic where an all-electric vehicle called Calypso will be operated from shore through the main field umbilical for up to 6 months between accessibility visits. Calypso, which will be called a resident ROV, will handle observation, maintenance, and light work tasks. On top of this, they are drawing on their experience supporting NASA and the space program to develop an electric manipulator that will match the functionality of today’s hydraulic manipulators.
6.3 Electric versus hydraulic 137