Forum Comanche and Mohican: Are Electric Work-Class ROVs the Future?

Forum Energy Technologies' Comanche and Mohican represent the most serious challenge to hydraulic dominance in the work-class ROV segment. Both are electric-drive vehicles designed to perform heavy subsea work without an on-board hydraulic power unit, using high-power brushless DC thrusters and electro-hydraulic tool power units for tooling interfaces. The industry has been skeptical of electric work-class for two decades — the Forum vehicles are the most compelling argument yet that the skeptics should start updating their assumptions.

Comanche: Technical Specification

• Depth rating: 6000m, making it one of the deepest-rated work-class electric vehicles available
• Payload capacity: 285 kg front payload plus 100 kg lateral payload — competitive with mid-range hydraulic work-class vehicles
• Thruster count: eight thrusters in a vectored configuration, with each thruster independently driven by a dedicated motor controller node
• Total installed power: 202 kW from the umbilical, of which approximately 150 kW is available for propulsion and tooling under steady-state conditions
• Tool package: integrated electro-hydraulic tool power unit rated at 138 bar / 60 L/min, sufficient for Schilling Titan 4 manipulator and standard torque tooling
• Primary manipulator: Schilling Titan 4 seven-function (standard) with CONAN grabber as secondary — identical tooling interface to the Millennium Plus and UHD
• Control system: Forum VMAX, described in detail below

Mohican: North Sea Optimization

The Mohican is Forum's regional derivative of the Comanche concept, developed specifically for North Sea operating conditions. The key differences from the Comanche are a reduced depth rating (2000m versus 6000m), a more compact form factor optimized for vessel deck space constraints typical in North Sea vessel spreads, and an enhanced heating system for the electronics enclosures to maintain operating temperature in 4°C bottom water. The Mohican also incorporates a storm-lock mode in the VMAX control system that prioritizes thruster allocation to heading and depth hold when vessel motion exceeds defined heave limits — this addresses a specific operational problem in the North Sea where surface vessel motion on ROV launches significantly stresses the tether system during descent and ascent. Forum has positioned the Mohican directly against the Oceaneering Millennium Plus in the North Sea IMR market, competing on total cost of ownership rather than raw capability.

VMAX Control System

Forum's VMAX control system is the most sophisticated ROV control architecture commercially available in the work-class segment. VMAX uses a model-predictive control framework — the system continuously updates a hydrodynamic model of the vehicle based on observed thruster response and current loading, then uses this model to compute the optimal thrust allocation for the demanded motion. In practice, VMAX produces significantly smoother station-keeping in variable current than conventional PID-based auto-functions used in Schilling/Beacon and Oceaneering control systems. Pilots reporting on VMAX consistently note that depth and heading hold in 1-2 knot crosscurrent requires substantially less manual override than on comparable hydraulic vehicles. The trade-off is that VMAX's model-predictive loop has a higher computational latency than simple PID control — there is a brief but detectable pause between pilot input and vehicle response at the start of a manual maneuver, particularly in surge. Pilots transitioning to VMAX report this as the most significant adaptation challenge.

Electric vs Hydraulic: Reliability Data

• Forum has published operational data from early Comanche deployments showing mean time between failures (MTBF) for the electric propulsion system approximately 2.3x higher than comparable hydraulic thruster systems on equivalent-class vehicles over the same operational period
• The elimination of the on-board HPU removes the single largest maintenance item on hydraulic work-class vehicles — HPU overhauls at 1000-hour intervals are a significant cost and downtime driver for hydraulic fleet operators
• Electric thrusters on the Comanche and Mohican are rated for 3000 hours between bearing inspections — hydraulic thrusters on equivalent vehicles typically require bearing inspection at 1500 hours
• The electro-hydraulic tool power unit (EHPU) on the Comanche introduces a hydraulic subsystem for tooling — this EHPU has its own maintenance requirements and failure modes, though it is a simpler system than a full vehicle HPU
• Umbilical power losses due to heat buildup in the dynamic cable — a known failure mode in hydraulic vehicle umbilicals running high-power HPU electrical feeds — are reported as lower on the Comanche due to a more efficient power distribution architecture

Maintenance Advantages in Practice

• No HPU fluid changes — hydraulic work-class vehicles require 200-400 liters of hydraulic oil changed at regular intervals; eliminating this removes the associated waste disposal costs and offshore handling hazard
• Thruster seal kits are simpler than hydraulic motor seal kits and require less specialized tooling — an experienced technician can complete a Comanche thruster seal replacement in under two hours
• Fewer subsea connectors in the propulsion circuit — each hydraulic thruster on a conventional vehicle requires two hydraulic hose connections plus a sensor cable; the Comanche's electric thrusters require a single power cable and a signal cable
• Motor controller diagnostics are available in real time through the VMAX system — developing bearing wear shows up as increasing motor current draw before failure; this predictive indicator is not available on hydraulic thrusters
• Tooling EHPU maintenance is isolated from propulsion maintenance — a EHPU service does not require disassembling any propulsion components, unlike HPU maintenance on hydraulic vehicles where propulsion and tooling share the hydraulic circuit
• Log all maintenance actions against vehicle running hours in ThrusterLog to build the maintenance-predictive dataset that Forum's VMAX system can optionally ingest for fleet health monitoring

Where Electric Work-Class Still Struggles

The honest answer to the title question is: not yet for the heaviest work, but closer than the industry acknowledges. The Comanche's 285 kg payload, while impressive for an electric vehicle, is below the payload envelope of the Millennium Plus on heavy lifting configurations where work basket and deployment frame mass pushes payload demand above 350 kg. Maximum sustained thruster force on the Comanche is approximately 170 kgf total — sufficient for most IMR and pipeline work but below what a fully-powered Schilling UHD can deliver in sustained high-load conditions. The EHPU's 138 bar / 60 L/min rating is adequate for the Titan 4 manipulator and most torque tools, but operations requiring simultaneous high-flow dredge plus manipulator plus vehicle station-keeping can approach the combined power budget limit in ways that hydraulic vehicles with dedicated HPU circuits do not experience.

Industry Adoption and the Future