One of Scotland's l­eading maritime experts has claimed that taxpayers' money is being wasted on a massive scale by the state-owned ferry company CalMac because of its insistence on fitting its latest small vehicle ferries with expensive hybrid engines, capable of running on both traditional diesel power and electric batteries.

The hybrid vessels will cost around £12 million, whereas a conventional ferry of a similar size would cost around £4m. It is expected to be launched in spring 2016 and will be able to accommodate 150 passengers, and 23 cars or two HGVs.

The comments were made by Alf Baird, professor of maritime business at Edinburgh Napier University, following last week's announcement that Port Glasgow's Ferguson shipyard had won its first ferry contract since being rescued by engineering tycoon Jim McColl last month.

Baird said the environmental benefits claimed for the hybrid ferries are "marginal" as the ferries will only be used in their electric mode for around 15% of the time when they are manoeuvring or alongside in port.

The Scottish Government contract will see the Inverclyde yard build its third hybrid ferry for CalMac as part of a programme to build four such vessels for some of its shorter west coast routes. It follows the introduction last year of the MV Hallaig on the Sconser to Raasay route on Skye, and the MV Lochinvar on the Tarbert to Portavadie run in Argyll and Bute.

Caledonian Maritime Assets Ltd (CMAL), the Government company which owns CalMac's ferry fleet, said the new ferries are the world's first sea-going vehicle and passenger ferries to use such hybrid technology.

But Baird said: "It is a dog's breakfast. No private-sector ferry company would buy these. Only the public sector would do this.

"There will be 10 to 15 tonnes of battery on these ferries. For a ship that is only designed to carry two trucks that is a hell of a lot of deadweight."

The ferries have four fuel-use modes: diesel only, a combination of battery and diesel power, battery only, or plugged into shoreside mains. When operated in electric battery mode, the ferries will produce no emissions at all.

Hybrid ferries charge their six-tonne lithium ion batteries overnight when mains electricity is cheaper while they are moored at their home ports. CMAL said the new technology will allow each vessel to save around £19,000 a year in fuel costs.

As the new vessels can be powered in harbour waters entirely using electric battery power, it is claimed that air quality as well as noise pollution in harbours will improve.

Carbon dioxide emissions will be reduced by at least 800 tonnes over five years, and emissions of sulphur and nitrous oxides will also fall.

CMAL said that using such hybrid technology will mean that the ferries use less fuel and produce carbon dioxide emissions at least 20% lower than the diesel-powered vessels that they replace. CMAL also claims the new ferries will have lower maintenance costs than conventional ferries.

Baird added that any reduction in noise while the ferries are in port will improve the quality of life of very few people, as the ports served by the new ferries are sparsely populated.

A spokeswoman for CMAL admitted that the cost of the new ferries was high but said that, with an expected lifespan of up to 35 years, the fuel savings and emission reductions would be significant.

However, she said: "Construction of the ferries involves a very high percentage of components supplied by third parties, therefore economies of scale do not feature when only building a small number."

The spokeswoman said no decision has yet been taken on the route for the third hybrid ferry. No decision has yet been made on when the fourth hybrid ferry will be commissioned.