The significant growth in their physical size and capabilities over the past few years has resulted in electric ROVs often proving to be nimbler, greener drivers of smarter and more cost-friendly operations. This is largely due to major technical advancements across a wide scope of areas and has sparked a vibrant debate about whether they are closing the gap on their larger hydraulic cousins.

These technology advancements range from data multiplexers, fiber optics, DC propulsion, open-frame design and smaller sensors to high-voltage power transmission, auto functions, increased diagnostics, increased reliability, low-density buoyancy, smaller manipulators and discrete hydraulic power packs.

Sub-Atlantic has manufactured cutting-edge electric observation-class ROV systems and components that have become the industry standard for hydraulic work-class ROV systems. The company has continued to build on its solid track record, recently securing a second contract with Italian oil and gas subsea services provider AALEA to deliver one of its class-leading Tomahawk observation ROV systems.

More sophisticated
“Electric ROVs have fast moved on from the days when they were basically flying cameras,” said Ryan Lumsden, global product director for Sub-Atlantic. “Now they carry out a multitude of tasks due to major advancements, particularly in the assortment of manipulators, tooling and sensors they can be fitted out with.

“As a result, they have become much more sophisticated in terms of their capabilities and in more complex and challenging environments, with smaller ROVs performing tasks previously completed by larger systems.”

Since its inception in 1997, Sub-Atlantic has carved out a niche for itself as a company specializing in the design and manufacture of electric ROVs, tether management systems and subsea components. In 2007 it was integrated into what has now become Forum Energy Technologies alongside the group’s well-known Perry brand as part of Forum’s subsea division.

The company’s fleet of electric ROVs includes its Comanche, Mohican, Super Mohawk, Mohawk and Mojave vehicles, all of which benefit from its subCAN high-speed communications data network system.

Bridging the gap
The Comanche is Forum’s flagship electric ROV. Considered a light work-class unit, it was designed specifically to bridge the gap between observation and work-class systems.

“One of the key considerations when designing the Comanche was ensuring it had substantial intervention capability,” Lumsden said. “This was achieved by working with Schilling Robotics to develop manipulators that were compact enough to fit an observation-class ROV while retaining the capability of a work-class manipulator.”

This led to a short version of the well-known Orion 7P being developed, which gave the Comanche a fully closed-loop position-controlled seven-function manipulator. This ultimately resulted in manipulative capabilities that were previously not associated with electric ROVs due to the level of accuracy and control required combined with the amount of strength and reliability needed.

“Another key consideration was hydraulic power. Although the Comanche propulsion system was natively electrical—which is what differentiates electric from hydraulic ROVs—hydraulic power was needed for the manipulators and tooling. Therefore, a compact hydraulic power unit (HPU) was developed with particular consideration given to what tools the Comanche could use to ensure the HPU was sized appropriately. This meant the Comanche could run tools such as dredge pumps, torque tools, pumping and injection systems, cutters, water jetters, and other tools, which until this time had been connected with hydraulic work class,” Lumsden added.

Compact deepwater system
With a power system of 3,000 v (400 Hz) from surface to ROV, the intelligent power transmission makes the Comanche particularly suited for long tether excursions and deep live-boating operations due to reduced tether and main lift cable diameters. This, combined with a payload of up to 550 lb and a fully electric seven-thruster propulsion system configured to provide optimum thrust and lifting capability, means it is a compact system able to operate at water depths between 2,000 m and 6,000 m (6,500 ft and 20,000 ft).

In addition, its survey interfaces enable it to conduct high-spec survey work with spreads comprising dualhead multibeams, a fiber-optic gyroscope, a bathymetric system, a doppler velocity log, hydraulic boom cameras, a pipetracker, a wheeled skid, a CP with electric actuator and laser measurement equipment.

Compared to hydraulic work-class systems, the Comanche can deliver capex and opex reductions for companies because it is not only easier to operate, requires smaller crews and lower levels of maintenance, but it also needs less deck space, Lumsden said.

While acknowledging that the Comanche and electric ROVs in general can’t do everything that their hydraulic counterparts can, Lumsden is quick to point out, “For ultraheavy-duty work such as construction support tasks where the ROV aids the installation of huge subsea structures, a hydraulic work class is required. However, the fact remains that the crossover with electric has increased, and the gap has narrowed.”

Expanded operating envelope
“The expanded operating envelope of electric ROVs allows them to carry out many of the tasks traditionally done by hydraulic systems,” Lunsden said. “One of the major benefits of this is cost when you consider the capital purchase price is in the region of one-quarter compared with that of a hydraulic system.”

The other benefit is size, he added. For example, the Comanche ROV is considerably smaller and lighter than a hydraulic system, while the vehicle’s tether management system also is smaller and lighter, as is the umbilical cable and the launch and recovery system.

“Overall, this results in a more compact system footprint, which is important when vessel or rig space is limited. It also makes it more transportable, which again is useful for mobile systems that are regularly transferred between vessels of opportunity. Furthermore, using electrics rather than hydraulics for an ROV’s primary power source is more environmentally
friendly,” he said.

The benefits of electric ROVs have been widely recognized in Europe, where they are predominantly used, in addition to the Middle East and Far East. Lumsden believes there’s less uptake in other regions such as the U.S. and Gulf of Mexico partly due to Europe having more stringent inspection, maintenance and repair regulations and also simply because no one considers looking beyond the more commonly used hydraulic work-class models.

“It’s a huge oversight—a bit like cracking a nut with a sledgehammer,” Lumsden said. “But as the global focus on improving cost and production efficiency across the industry continues to heighten, I anticipate attention in these provinces will start to turn to electric ROVs as a much more compelling alternative.”

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