How electric ferries work: inside the battery push replacing diesel boats

Electric ferries run on the same basic principle as an electric car: large batteries store energy and feed it to electric motors that turn the propeller or thruster, with no diesel engine involved during normal operation. The technology has moved from a single Norwegian pilot boat a decade ago to fleet-wide procurement programmes in Scotland, with Highland Council confirming on 2 October 2026 that it has formally launched the tender for a new electric vessel to replace the Corran Ferry across Loch Linnhe, according to the council's own announcement.

How the propulsion system works

The reference case for the technology is MF Ampere, built by the Norwegian shipyard Fjellstrand and delivered in October 2014 for operator Norled, which began commercial service in May 2015 as the world's first fully electric car and passenger ferry, according to Ship Technology. The 80-metre aluminium catamaran carries up to 360 passengers and 120 cars across a 5.7km crossing of the Sognefjord, making around 34 trips a day at a cruising speed of 10 knots.

Ampere's two onboard electric motors, rated at 450kW each, are powered by a 1,000kWh lithium-ion battery pack weighing about 10 tonnes, Ship Technology reported. One motor drives Rolls-Royce Azipull thrusters fitted with a feathering controllable-pitch propeller, which lets the ferry manoeuvre without a separate rudder. Because the thrusters can rotate, the same system handles both propulsion and steering.

The batteries recharge during the roughly ten minutes it takes to load and unload vehicles at each pier. Siemens Energy, which supplied the propulsion package, said the local power grid was too weak to deliver that much energy in such a short window, so Norled and Siemens installed buffer batteries at each shore station — 260kWh units that charge from the hydroelectric grid and discharge quickly into the ferry's onboard batteries during the stop.

Why operators are switching from diesel

Siemens Energy said the Ampere model cuts fuel costs by up to 60% compared with an equivalent diesel ferry and that battery-hybrid retrofits on other vessels have saved up to 90% in fuel consumption, emissions and running costs. The company cited a separate case, the Bastø Electric, which it described as the world's largest all-electric car ferry and said cut CO₂ emissions by 75% in 2022. It also referenced a Siemens Energy/Bellona study estimating that fully electrifying ferry fleets in several European countries could cut emissions in those fleets by close to half, saving an estimated 800,000 tonnes of CO₂ annually using currently available technology.

Maritime transport as a whole produces about 3% of global greenhouse gas emissions, and Siemens Energy noted that 81% of the roughly 91,000 ships in the world fleet are small or medium-sized vessels — the category most of these ferries fall into and the segment where battery-electric propulsion is considered most technically and economically feasible given short, fixed routes and predictable charging windows.

Scotland's fleet-wide rollout

The Ampere approach has since been scaled into a fleet procurement programme. Caledonian Maritime Assets Ltd (CMAL), the body that owns vessels and harbour infrastructure for Scotland's state-run ferry network, is running a Small Vessel Replacement Programme covering seven initial 50-metre electric ferries for west-coast routes including Colintraive–Rhubodach, Lochaline–Fishnish and Iona–Fionnphort, with three further vessels planned for a second phase, according to industry publication Riviera Maritime Media, which cited the shipyard building the vessels.

Each of those ferries is being built with close to 6 megawatt-hours of battery capacity using Corvus nickel-cobalt-aluminium cells, which Riviera Maritime Media reported is more than 30% lighter than lithium-iron-phosphate batteries of equivalent capacity — a significant factor given the weight limits on small vessels. CMAL said the boats are designed to operate up to 14 hours a day and fully recharge overnight in under 10 hours; deliveries are scheduled to begin in the third quarter of 2027 and continue at three-to-four-month intervals through the first quarter of 2029. CMAL currently runs 17 small vessels on the west coast, several of them nearing the end of their service life, alongside three existing hybrid diesel-electric ferries built between 2012 and 2016.

The Corran Ferry replacement

The Corran crossing, one of Scotland's busiest single-vessel ferry routes, is currently served by the MV Corran, which has operated since 2001, according to broadcaster STV. Highland Council said the replacement project is funded with £58 million from the Inverness and Highland City-Region Deal, made up of £28 million from the Scottish Government earmarked for the new electric vessel itself, £20 million from the UK Government, and £10 million from Highland Council for landside works such as slipways and charging infrastructure.

Working with CMAL, which is providing technical expertise and procurement support, the council launched a single-vessel tender on 2 October 2026. The council said it expects to award the build contract in March 2027, with landside infrastructure finished by June 2027 and shore-based charging equipment installed and commissioned by September 2028, ahead of the new ferry entering service in early 2029. The new vessel will be a roll-on/roll-off design, built to the standardised specification used across CMAL's Small Vessel Replacement Programme. STV reported that the existing MV Corran will be kept on as a relief vessel once the new electric ferry takes over the route.

What still limits the technology

The Siemens Energy material and the Riviera report both point to the same underlying constraints: battery weight relative to a vessel's carrying capacity, the strength of the local electricity grid at charging points, and the need for very fast turnarounds so ferries can recharge in the few minutes they spend loading passengers and vehicles. These factors explain why battery-electric propulsion has so far been deployed mainly on short, fixed routes with predictable schedules — such as fjord crossings and inter-island links — rather than on long open-sea voyages.