The scandal-hit Glen Sannox ferry will emit even more carbon than the boat it is replacing despite Nicola Sturgeon boasting it would help tackle climate change.
The ‘dual fuel’ CalMac boat will pump out the equivalent of at least 10,391 tonnes of CO2 each year when it starts regular crossings to Arran on January 13.
That is a third more than the 7,732 tonnes put out by the 31-year-old diesel Caledonian Isles used on the route.
The Scottish Tories said the new ferry’s green credentials were yet more SNP ‘spin’.
The Glen Sannox and Glen Rosa were ordered from the Ferguson Marine yard on the Clyde in 2015 for a ‘fixed price’ of £97million and were due to be delivered in 2018.
But they were plagued by delays and cost overruns, and the total bill is now £428million.
A key reason for the problems was the Scottish Government’s ferry procurement arm, CMAL, ordering dual fuel ferries, the first ever built in the UK.
These can run on traditional marine gas oil (MGO diesel) and liquefied natural gas (LNG).
When Ms Sturgeon helped launch the Glen Sannox in 2017 as first minister, she said both boats would be ‘contributing to Scotland’s world-leading climate change goals’.
But the BBC yesterday reported a confidential CalMac study had found that, because the Glen Sannox is bigger and more powerful, it will emit more carbon than its predecessor.
If the Glen Sannox ran purely on MGO its CO2 emission would be equal to 11,375 tonnes.
Running on LNG alone it would be 10,391, but using LNG also releases unburnt methane, adding another 1,800 tonnes of CO2 equivalent.
Professor Tristan Smith, of University College London’s Energy Institute, told the BBC: ‘In a best case scenario there’s a negligible benefit of using LNG, and at worst there would be a deterioration.’
He said LNG was cleaner than MGO from an air pollution perspective but ‘doesn’t have any advantage from a climate perspective’.
There was even a case for running the Glen Sannox on MGO diesel all the time, he said.
Joe Reader, chair of the Mull & Iona Ferry Committee, said there seemed to have been ‘blind’ decision-making on dual-fuel.
‘The outcome all these years later is hundreds of millions of pounds of what seems to be a very expensive mistake,’ he said.
Tory energy and net zero spokesman Douglas Lumsden said: ‘The SNP’s claims that the Glen Sannox would be eco-friendly looks to be yet more spin.
‘Meanwhile the SNP have squandered hundreds of millions of taxpayers’ money.
‘They must urgently set out how they intend to mitigate the harmful emissions produced by this delayed and over budget vessel.’
A CMAL spokesman added: ‘Due to the difference in vessel size, propulsion power and expected sailing time, it is inaccurate to draw direct comparisons between the emissions of older vessels and MV Glen Sannox.’
State ferry operator CalMac said passenger and vehicle numbers on the Arran route had increased significantly over the past 30 years.
A spokesman said: ‘More power is needed for the size of the vessel that can meet that demand, particularly carrying cars, and it should offer greater resilience against adverse weather.
‘We will learn more and more about MV Glen Sannox and her fuel consumption as we sail her.’