Electric Work-Class ROVs Are Replacing Hydraulics

Hydraulics won the first forty years of subsea intervention for a simple reason: a hydraulic actuator delivers enormous force from a small package, and pressure-compensated hydraulic systems tolerate depth without complaint.

They also leak. Every fitting, every rotary joint, every hose is a place where oil can escape into the sea and seawater can find its way in.

What went first

Observation-class vehicles were electric from the start, because they never needed the force. The interesting transition is work class, where the manipulators and tooling are the entire point.

Forum Energy Technologies announced the Quantum EV in 2019 and had it in the water for testing by 2022.¹ Saab Seaeye's eWROV was covered in 2023 as a full-size all-electric work-class vehicle, described in trade coverage as reportedly the first of its kind.² Saipem's Hydrone-W, all-electric, was scheduled for Njord in 2021. Oceaneering unveiled the Momentum electric work-class ROV in 2026 coverage, aimed explicitly at long-duration subsea residency.³

Forum now lists a fleet of electric vehicles including the Atom EV, Comanche, the Mohawk and Mojave family and the XLX EVO III.¹

Why it took twenty years

Force density. A hydraulic ram produces more force per kilogram than an electric actuator, and at the top end of work-class tooling that gap was decisive for a long time.

What closed it was not one breakthrough but three converging: permanent-magnet motors improved, power electronics got smaller and more efficient, and pressure-tolerant electronics stopped requiring a one-atmosphere housing for everything. A motor that can sit in oil-filled compensation rather than a thick titanium can changes the whole packaging problem.

What removing the hydraulics gets you

Fewer things that fail slowly. A hydraulic power unit, its reservoir, filters, accumulators and every hose run disappear, and with them a large share of the maintenance schedule.

Efficiency improves because electric actuation draws power only when it does work. A hydraulic system runs its pump continuously and dumps unused flow over a relief valve as heat, which is wasted energy on a vessel and a thermal problem in a sealed subsea garage.

Control gets better. Electric actuators are directly and precisely commandable in a way that valve-controlled hydraulics are not, which matters for delicate manipulation and for any attempt at automating a routine task.

And no oil goes in the water. Environmental permitting for offshore work has tightened steadily, and a vehicle with no hydraulic fluid to lose has one fewer argument to have.

What you give up

Peak force at the top end. A heavy work-class hydraulic vehicle doing structural intervention still exceeds what electric tooling delivers, and for those jobs hydraulics remain the answer.

Cost is higher up front. The saving is in operations over the vehicle's life, which is an easy argument for an operator running its own fleet and a harder one for a contractor bidding a single campaign.

And the installed base is enormous. Thousands of hydraulic vehicles are working now, with spares, trained crews and established maintenance practice behind them. Fleets turn over slowly.

Why residency is forcing the pace

A vehicle parked subsea for a year cannot have anything that needs topping up, bleeding or replacing.

Every hydraulic leak point on a resident vehicle is a failure nobody will reach for months. That constraint is why the electric transition and the residency trend arrived together rather than separately, and why Oceaneering's Momentum is described in terms of subsea residency rather than in terms of thrust.

The vehicles are not being made electric because electric is better in the abstract. They are being made electric because the deployment model that saves the most money will not tolerate hydraulics.