“Battery-First Power”: Inside Bibby Marine’s new eCSOV Vessel Design

In maritime, the best technology stories are rarely about a single piece of equipment, rather the integration of technologies, vessel design and operating profile in a way that fundamentally changes how a ship does its job.

That is the story behind Bibby Marine’s new Eco Construction Service Operation Vessel (eCSOV), currently under construction at Armon Shipyard in Vigo, Spain, for commissioning in mid-2027. Working with naval architect Seaplace, battery supplier Corvus Energy and propulsion specialist Kongsberg Maritime, Bibby Marine has designed an offshore wind vessel around what Gavin Forward, Vessel Newbuild Director, Bibby Marine, calls a “battery-first power philosophy.”

The distinction is important.

This is not a conventional diesel-powered vessel with a battery installed to shave peaks. Instead, the battery bank is the primary source of power, fundamentally changing how the engines, propulsion system and vessel itself are designed and operated.

And in an interesting twist, one of its headline environmental benefits — a potential 40% to 60% reduction in underwater radiated noise (URN) — was not actually the starting point.

“We didn't design this vessel specifically around minimizing Underwater Radiated Noise,” Forward said. “Rather a lower URN is a welcome benefit of a vessel that's ultra efficient and battery powered.”

That perhaps best illustrates what makes the vessel noteworthy: efficiency, emissions, noise, maintenance and economics are interconnected rather than separate design targets.

Image courtesy Bibby Marine

We're designing a vessel specifically to support the offshore renewable energy,” he said. “So we should be looking at its total environmental impact, not simply the carbon emissions.”

- Gavin Forward,
Vessel Newbuild Director, Bibby Marine

Battery First

Bibby Marine has more than two centuries of maritime history, dating to 1807. Today its marine operations center on offshore wind — including two Wavemaster SOVs — and five floating accommodation assets. Wavemaster 1 entered service in 2017 as what Bibby describes as the first purpose-built walk-to-work vessel. Its new eCSOV represents the next technological step.

At just under 90 meters long and 20 meters wide, it will accommodate 120 personnel in 90 single cabins. A 3D motion-compensated gangway and crane support personnel and logistics transfers, with the gangway capable of operating from either side of the vessel. The design is also prepared for an electric daughter craft that can be charged directly from the mother ship.

But the heart of the vessel is Corvus Energy’s 24.4-MWh Blue Whale NextGen lithium iron phosphate battery system, integrated into a 1,000V DC electrical architecture divided into three sections for redundancy.

Propulsion comes via Kongsberg Maritime rim-drive thrusters.

The battery-first philosophy means that, unlike conventional hybrid vessels where batteries supplement engine-generated power, Bibby’s battery is the primary power source. When offshore charging infrastructure is available, the vessel can take renewable electricity directly from the wind farm and operate fully electrically.

Where charging is unavailable, Bibby switches to what it calls “hybrid-plus” operation. Dual-fuel methanol/diesel engines run at a fixed, efficient load to recharge the batteries and then shut down rather than continuously ramping up and down following vessel demand.

Forward said the batteries can be recharged offshore using the engines in approximately four to five hours. The vessel can subsequently operate for more than 24 hours on batteries alone and sail approximately 150 nautical miles electrically. E-methanol provides another pathway for extending zero-emission operations.

Designing Out the Noise

The architecture delivers an intriguing secondary benefit: rather than insulating machinery to reduce noise, Bibby can simply switch much of that machinery off.

On a conventional CSOV, engines, generators, gearboxes, pumps and rotating equipment generate vibration that can migrate through the hull into the surrounding water. Propellers and thrusters add another major source, particularly through cavitation.

“Rather than trying to reduce that noise, we just get rid of that noise altogether,” Forward said.

The battery removes one half of the equation. Kongsberg’s rim-drive propulsion tackles the other.

With the electric motor integrated directly into the propeller, the thrusters eliminate the conventional gearbox and its associated mechanical vibration and tonal noise. The rim-drive design also provides more balanced water flow through the propeller, reducing cavitation.

Together, Forward expects the battery-first architecture and rim drives to deliver a 40% to 60% reduction in underwater noise. Bibby is targeting DNV Silent E and Silent A notations.

That matters particularly during dynamic positioning.

A CSOV can spend large portions of its working life stationed alongside offshore wind turbines, with thrusters continuously adjusting power and direction to hold position while personnel cross the gangway.

Instead of generators constantly ramping in response to those rapidly changing loads, Bibby’s batteries respond directly. The gangway itself can operate from port or starboard and at heading angles up to 60 degrees, allowing the captain to position the vessel more favorably relative to wind, waves and current.

Better positioning means less energy. Less energy means less thrust. And less thrust means less noise.

Why URN Matters

Forward argues that underwater noise must increasingly be considered alongside greenhouse gas emissions when measuring offshore wind's environmental footprint.

An SOV does not simply visit a wind farm during construction. These vessels can work around the clock throughout an offshore project's operational life — potentially 20, 30 or 40 years.

The cumulative acoustic footprint therefore matters.

URN is increasingly recognized as marine pollution, Forward said, while offshore wind developers are paying greater attention to the issue during project consenting. “We're designing a vessel specifically to support the offshore renewable energy,” he said. “So we should be looking at its total environmental impact, not simply the carbon emissions.”

The Business Case

For shipowners, however, technology ultimately has to survive the spreadsheet.

When Bibby began serious design work in 2023, battery prices made the commercial proposition difficult. Forward said battery prices have subsequently declined by as much as 70% while energy density and performance improved. The first vessel received UK government support to help bridge the first-of-kind cost gap. But Bibby has continued optimizing its next Series 2 design, and Forward said its capital cost is now within 10% of a conventional vessel.

More important may be what happens after delivery.

Running engines fewer hours reduces fuel consumption, maintenance and machinery wear. Electrification can also reduce exposure to future carbon costs and emissions charges. Bibby calculates that over a 10-year wind farm charter, an electric SOV could generate approximately $6 million in operating-cost savings versus a conventional vessel.

That turns the traditional argument surrounding green vessel technology on its head.

“The technologies that reduce the underwater noise in our case also improve the efficiency and reduce the OPEX,” Forward said.

There are human benefits, too. Less vibration and machinery noise create a quieter, more comfortable environment for crew and technicians who may spend weeks aboard.

The result is a vessel where the environmental and commercial cases increasingly converge.

Build for Tomorrow

Perhaps the most compelling aspect of Bibby Marine’s eCSOV is that no single component tells the story.

Corvus Energy provides the large battery system. Kongsberg Maritime's rim drives reduce mechanical losses, vibration and cavitation. Seaplace's vessel design enables the operational flexibility that reduces DP power demand. Offshore charging potentially connects the vessel directly to the renewable-energy infrastructure it exists to service.

Together, they create something larger than a collection of advanced equipment.

For Forward, that is the lesson for shipowners contemplating their next generation of vessels.

“Design for where the industry's going rather than how it's been done in the past,” he said.

Electrification, he argues, should not be viewed simply as a decarbonization requirement. It offers flexibility in where vessel energy comes from and potentially gives operators greater ability to secure energy costs over longer periods.

“Look at it as an opportunity to build a better, more efficient, and more resilient vessel.”

For an industry accustomed to incremental improvements, that may be the most important feature aboard Bibby Marine's new eCSOV.

Main particulars

• Length overall: 89.63m

• Breadth molded: 19.80m

• Depth molded: 7.55m

• Draft (design): 5.00m

• Trial speed: 13.0 knots at 5.0 m draft in calm weather and with clean hull
  10 knots at 5.0 m draft, eco speed.

• Gross tonnage: 6773Te

• Fuel oil (MGO): 501 m³

• Fuel oil (methanol): 450 m³

• Fresh water: 270 m³

• Warehouse area: 535 m²

• Cargo deck area: 500 m²

• Deadweight: 2283 t

• Flag: UK

• Engines: Wartsila 6L32, dual fuel methanol

• Power: 2x 3480 kW @ 750rpm, 50Hz

• Combined power: 6800 kW(e)

• Emergency genset: 1x ~365 kW

• Energy storage system: Corvus Energy
  Lithium iron phosphate (LFP)
  24,400 kWh
  Split across 3 compartments
  Offshore charging

• Thrusters: Kongsberg
  2x 2000 kW RIM Drive Main Azimuth units
  2x 1500 kW RIM Drive Tunnel units
  1x 1200 kW Retractable unit

• Classification: DNV +1A Windfarm Service, battery power, E0, LFL fuelled, DYNPOS(AUTR-CB), OMF(C-2, V-2), SPS, Walk-to-Work, Clean (Design, Tier III), Cyber Secure (Essential), LCS, BIS, Strengthened(dk), Smart(EEN), BWM(T), ER(SCR), HELDK(SH), recyclable, shore power, NAUT (OSV); Expected to meet SILENT E (environmental) & SILENT A (acoustic)