A new wave of delays to the two vessels at the centre of Scotland's ferry fiasco have been signalled because of an "emerging risk" over the use of so-called green fuel.

Ministers have been told by Ferguson Marine that there have been delays to the supply of vital piping systems that should have been taken place at the end of 2023.

But the Scottish Government has been told that the installation won't be complete till the middle of March and that there would be a further ten weeks of testing required.

It came after the nationalised yard company identified at the end of last year that there had been an "emerging risk" to the liquefied natural gas (LNG) system on Glen Sannox.

It meant that the entire system required specialist cryo-steels to be installed.

READ MORE: Island told to prepare for food shortages in CalMac ferry row

It has meant the symbolic launch date of the second vessel Glen Rosa has had to be put off from March 12 to April 9.

The yard has said it allows for critical work on Glen Sannox in March.

It comes as the much-delayed Glen Sannox ferry was preparing to sail under its own power on February 13 in the Clyde between the Port Glasgow shipyard and Gourock.

The ferries were lauded by then First Minister Nicola Sturgeon as the 'sustainable' ferries that would "contribute to Scotland's world-leading climate change goals".

Glen Sannox and Glen Rosa were to be able to operate on LNG which the Scottish Government ferry owners Caledonian Maritime Assets Ltd said was "significantly cleaner and will help to reduce emissions to meet ambitious Scottish Government targets".

The Herald: Glen Sannox

They were hailed as a step towards a greener future for Scotland's state owned CalMac ferry fleet as they were to be the first UK-built ships capable of running off LNG as well as conventional diesel.

CMAL has previously said that the two vessels would reduce the carbon footprint of the ferry fleet by 25 per cent.

But the Herald revealed that the European Federation for Transport and Environment, commonly referred to as Transport & Environment, a European umbrella for non-governmental organisations working in the field of transport and the environment, promoting sustainable transport in Europe believe the ferry engines chosen are the worst for methane greenhouse gas leakage.

They say using LNG as a marine fuel goes against the Global Methane Pledge launched at the United Nations Climate Change Conference, commonly known as COP26, in Glasgow in November 2021 that aims to reduce methane emissions by 30% by 2030 and is against advice from institutions such as the World Bank.

Both ferries, Glen Sannox and Glen Rosa were due online in the first half of 2018, with one intitially to serve Arran and the other to serve the Skye triangle routes to North Uist and Harris, but are at least six years late, with costs expected to be quadruple the original £97m contract. It has been confirmed that both are now to serve Arran.

Glen Rosa was meant to be delivered to CalMac in August 2018, but that is currently scheduled for May 2025. Glen Sannox, was launched by Nicola Sturgeon nearly seven years ago and is due for delivery in the spring.

But the dates of arrival have been constantly in a state of flux as their construction has been plagued by design challenges, cost overruns and delays.

The Herald: David Tydeman of Ferguson Marine

Now Ferguson Marine chief executive David Tydeman has told ministers that the LNG issues will have a bearing on the final handover of Glen Sannox and Glen Rosa as well as overall costs to complete impacts for both ships.

A ferry user group official said that it was the "latest in the long running saga of mismanagement of  the delivery of ferries".

"It is quite remarkable that even after all that has happened, we still have not got a full handle on the costs and the timing of these crucial ferries which are so important to not just islanders but to visitors who spend their tourist money in this country," he said.

Eyebrows have already been raised about the logistics of getting LNG to Scotland – while four new vessels being built in Turkey will not be powered by the 'green' fuel at all.

According to a 2022 Scottish Government briefing, LNG will have to be shipped from the Isle of Grain in Kent – a near 500 mile journey by road.

CalMac has been told that it is not yet feasible to use LNG-powered trucks due to the size of the fuel tanks required and a lack of refuelling infrastructure.

The adoption of LNG as a fuel by ships stems from the fact that LNG contains less carbon and little sulphur compared to traditional marine fuels. LNG can thus lower CO2 and sulphur oxides (SOx) emissions that ships would normally emit. LNG marine engines are also set up in a way that emits less nitrogen oxides (NOx) emissions.

When LNG is burned as a fuel, it releases energy and produces carbon dioxide (CO2) and water vapour, along with smaller amounts of other pollutants.

While CO2 is a significant greenhouse gas, burning methane releases less CO2 compared to other fossil fuels, making in theory LNG a relatively cleaner-burning fuel.

Transport & Environment say that while the industry was quick to tout the benefits of LNG, the relatively damning methane slippage problem was swept under the carpet, as well as leakages from on-shore infrastructure associated with the fuel's production, transportation and storage.

If methane is released in air – even in very small amounts – its impact on climate change is disastrous.

Four new vessels being built to support CalMac's ageing ferry network being built in Turkey will be diesel/electric hybrid propulsion vessels – not LNG.

It means the LNG infrastructure plans will presently be for just two vessels – and there have been persistent questions over that as Ardrossan has not been ready for either the ferries on the fuel.

While there has been criticism over what has been described by some as an LNG planning 'farce', CalMac has begun moves to use Troon rather than Ardrossan for services to and from Arran from the summer of 2023. Because of the storage tank issues, the LNG will be pumped from trucks to the ship there.