Big battery, big savings: why a zero-emissions eCSOV makes sense

Carbon taxes

Another consideration in the vessel’s design are forthcoming taxes on carbon emissions resulting from regional regulations, the EU Emissions Trading System and FuelEU Maritime.

“We look at the taxes coming in for the carbon and they are going to be around about US$100 to US$300 per ton. There are three tons of CO2 produced per ton of fuel consumed. So that’s a huge cost,” he said.

Mr Forward anticipates running on power generated from the grid will be far less expensive. “Even if you take a relatively high price for the power off the wind turbine, we are still looking at saving around about a third of the cost per day on operating costs, or a fifth of the cost when we consider the taxes as well,” he stated. “Additionally, there is a huge environmental benefit doing this,” he added.

A ‘whale’ of a battery

A major driver of those environmental benefits will be the largest battery installation to date on an offshore vessel, and built-in offshore charging capability when it hits the water in Q2 2027.

“It will be the first offshore vessel that can charge offshore,” said Mr Forward, noting Bibby Marine did not want to have to upgrade the vessel later to incorporate the capability. “We have worked closely with offshore charging suppliers to ensure our systems are aligned,” he said.

A special dynamic positioning (DP) mode will allow the vessel to charge at the offshore wind turbine. “The idea is that we will be able to seamlessly charge the vessel while providing power to the thrusters to maintain position,” he explained.

A DC grid setup will minimise energy losses, and offshore charging systems will allow simultaneous battery charging and DP.

Mr Forward noted that the eCSOV’s design has evolved since the concept design was executed by UK ship designer Longitude. One of those changes has been to the battery chemistry, moving from lithium-titanium oxide (LTO) to lithium iron phosphate (LFP).

A 25 MWh Blue Whale energy storage system (ESS) will be supplied by Corvus Energy, company vice president, sales, Pål-Ove Husøy, revealed during the Annual Offshore Support Vessel Conference, Awards and Exhibition, held in London in February.

“A fully electric offshore vessel is something the industry has been working towards for a long time and marks a major milestone in offshore vessel operations,” Mr Husøy said.

Mr Husøy expects the ESS will provide enough power to operate in full electric mode for a “typical 16- to 17-hour day.”

In announcing the contract, Corvus said that unlike conventional hybrid propulsion systems, the eCSOV will use its battery system as its primary power source, with engines running “solely for charging”. This, Corvus said, offers a constant, optimised load to improve efficiency and extend battery life.

“We are looking at saving about a third of the cost per day”

“Additionally, offshore charging capabilities will enable simultaneous battery charging while maintaining DP for station-keeping, representing an industry first in the SOV market,” the ESS developer said.

The Blue Whale ESS received type approval from DNV in 2024.

Optimising performance

Bibby Marine began working with Madrid-based Seaplace when the owner signed a shipbuilding contract with Gondan Shipyard in Spain in 2024. After “an amicable move away” from Gondan Shipyard, the owner directly retained the Spanish naval architectural firm to continue the basic design, before signing a shipbuilding deal with Armon Shipyard in 2025.

The UK-flag eCSOV will have an overall length of 90 m, beam of 19.8 m, draught of 5 m, maximum speed of 14 knots and accommodation for 96 technicians and 24 crew.

Mr Forward said the design “has massively changed” since the original concept, including optimising the hullform. “The sea-keeping performance has improved in model testing. We can get one knot extra speed out the vessel than we had originally seen during the concept design,” he said.

“Internal spaces have completely been redesigned, and that’s really based on feedback we have had from operators on workflow,” he said. Methanol safety zones, piping and batteries have all impacted interior design as well.

For example, the eCSOV was originally conceived with five battery rooms; it now has three.

“Once we started speaking to Corvus, we managed to fit more battery capacity into each room, which meant that we could reduce the number of rooms. Once we optimised the design, we optimised the whole build,” he said.

Data gathering

Mr Forward and Mr Husøy both emphasised the importance of data collection for monitoring the performance of the vessel and its energy storage system, and cybersecurity. Big data, said Mr Husøy would be used to optimise the ESS and the vessel, and influence future design. He said both the ESS and vessel will have a cybersecurity notation from DNV.

“I don’t think any other vessel is going to have the amount of data collection that we will have,” said Mr Forward.

“AI modelling with a digital twin will push optimisation, not just from a capex perspective, but also from an operational one, making sure the crew is driving the vessel the most efficient way,” said Mr Forward.

Propulsion package

Armon Shipyard selected Kongsberg Maritime to supply a comprehensive propulsion, control and DP package for the DNV-classed vessel.

Under the contract, the Norwegian maritime technology provider’s scope of supply covers full-electric Rim Drive propulsion with azimuth and tunnel thrusters, as well as the automation system, full electrical control system, DP, and thruster control.

“All propulsion is electric and features Kongsberg’s permanent magnet technology,” Kongsberg Maritime vice president, sales, offshore support and construction units, Otter Ristesund said.

He said the units have a compact inboard footprint, saving valuable space on board, while their low noise and vibration levels minimise hydroacoustic noise, protecting marine life and improving onboard comfort.

“The thrusters are designed with minimal rotating parts, providing durability and reducing maintenance. They also offer enhanced manoeuvrability, delivering equal thrust in both directions to ensure excellent vessel control,” said Mr Ristesund.

The system will comprise two Rim Drive azimuth 2600 models for main propulsion, one retractable UL 155 thruster with a PM motor and two Rim Drive TT 200 tunnel thrusters.

“It is a complex design with a huge battery package and indeed, the first eCSOV,” said Mr Ristesund. “But with good co-operation among all the stakeholders we will, for sure, make this project a great success,” he concluded.