All aboard the battery-powered boat

The world's first sea ferry to be part-powered by batteries could be about to serve some of the company's Clyde and Hebridean routes.

It would effectively be the maritime version of a hybrid car like the Toyota Prius, cutting diesel consumption - and emissions - by at least 20 per cent.

Caledonian MacBrayne said the hybrid ferries could potentially serve nearly half its routes - 11 of the shorter crossings which don't require large vessels. They could include those linking the mainland to the islands of Gigha, Lismore and Raasay, along with secondary routes to Arran, Bute and Mull.

The firm which owns CalMac's vessels and harbours, Caledonian Maritime Assets Limited (CMal), said the first ferries could be ordered as early as next year and be in service around 2013.

The 145ft-long craft would carry 23 cars and 150 passengers, and travel at nine knots over routes of around four miles. They would use both battery and diesel power, with the batteries being recharged overnight in ports.

In a further environmental boost, the batteries could be replenished using wind energy generated at night, which might otherwise be wasted because of the limited demand for power in the small hours.

The batteries are expected to take as much space as a Transit van, with the hybrid technology adding 1m to the 6m cost per vessel.

Hybrid and battery vessels are currently limited to river ferries, such as in Germany, and tugs and ocean-going yachts.

CMal chief executive Guy Platten said the company hoped to win European funding for the project, both for the ferries and electricity sub-stations which would be required in harbours for battery recharging. Platten said: "We believe it will be the world's first sea-going vehicle passenger hybrid ferry. The intellectual property rights would rest with us, so Scotland could be a world-beater.

"We are focused on building for the future, so have to make sure we build sustainable ferries, which also contribute to the Scottish Government's targets on cutting climate change emissions."

Ferry companies now had to develop a different mindset about the design of ships, he added. "Ten years ago, fuel was pretty cheap."

But conventional diesel-powered back-up was necessary at this stage. "This is ground-breaking, but with life-line ferry routes such as those to the islands, the ferries will have to be reliable and able to run without batteries.

CMal is also seeking to involve other ferry operators, such as Shetland and Orkney councils, and is already in a new ferry development partnership with government departments in Northern Ireland and Ireland. Environmental campaigners welcomed the project. Dr Richard Dixon, director of WWF Scotland, said: "There may be a fairly long payback period for the cost of the technology, but it is a logical extension of hybrids on the road. If there are big batteries in a ferry, that's a great place for night-time wind power to go."

Using less marine fuel would also bring benefits, Dixon said. "Marine diesel is also higher in sulphur than road fuel because ship engines are less refined, which contributes to acid rain."

CalMac said its routes which potentially matched the criteria for hybrid ferries were: Claonaig - Lochranza (Arran), Tayinloan - Gigha; Colintraive - Rhubodach (Bute); Tarbert - Portavadie (Argyll); Oban - Lismore; Fionnphort (Mull) - Iona; Kilchoan - Tobermory (Mull); Lochaline - Fishnish (Mull); Sconser (Skye) - Raasay, Ardmhor (Barra) - Eriskay and Berneray - Leverburgh (Harris). However, these would depend on factors including the installation of new electricity supplies.

George Taylor, CalMac's technical director, said: "While shipping contributes a comparatively tiny amount of carbon emissions compared to aircraft and road vehicles, we are happy to play our part in reducing that as much as possible. One option which offers some exciting prospects is the use of hybrid power units, which are cleaner and cheaper to run.

"The technology is still very new and most easily adopted on the next generation of small ferries. It is likely to be many years before we have anything which could be used on large sea-going vessels, but we are watching developments with interest."

CalMac is also considering other green measures to save energy, such as high-efficiency propeller blades and new hull coatings. However, it said that although there were no plans to reduce ferry speeds because it would affect timetables, this could be considered for future operating contracts.

Transport minister Stewart Stevenson said: "CMal's innovative plans for a hybrid passenger ferry demonstrate the real opportunities that exist for Scotland to reap the benefits of the low carbon economy. Our world-leading emissions reduction targets include emissions from aviation and shipping, and eco-friendly vessels could play an important part."