TRIALS of the liquified natural gas (LNG) system on one of the delayed new Arran ferries have been postponed as it is taking longer than expected to load the fuel onboard.

With the deadline for handover of the Glen Sannox approaching on September 30, the state-owned shipyard Ferguson Marine has had to push back its LNG harbour trials, which were due to begin on Wednesday.

It has been reported elsewhere that the process of cooling the pipes to the sub-zero temperatures necessary to load the fuel is taking longer than anticipated.

Both Glen Sannox and sister vessel Glen Rosa were designed from the outset to be "dual fuel" ferries, able to run on both traditional marine gas oil and LNG.

However, problems with installing the LNG system have been behind some of the repeated delays in delivering the two ferries, with the Port Glasgow shipyard dealing with these issues over the past year.

Both ferries were originally earmarked for the Ardrossan to Brodick route.

But due to major issues with Ardrossan Harbour, the new vessels may have to sail from Troon at first - and perhaps longer term unless the Scottish Government approves a multi-million upgrade of the North Ayrshire port.

A Ferguson Marine spokesperson said: "LNG harbour trials were due to begin on Wednesday with the loading of LNG at quayside. However, it is taking longer than initially advised to cool the pipes to the required temperature to load the LNG.

"The additional cooling time needed means the trials will be rescheduled.

"Once the required temperature has been reached, the schedule will be redefined, with new dates likely to be agreed before the end of this week."

Ferguson Marine said the official handover date remains September 30, though this could be pulled forward if sea trials are successfully completed.

Current cost estimates for Glen Sannox are between £145.5 million and £149.1 million and it is hoped the cost of Glen Rosa will be kept below £150 million.

Now six years late, the total bill will be three times the original £97m price tag.

David Tydeman, who was chief executive of Ferguson Marine until March, previously said that loading LNG is a "complicated" process involving purging the pipelines of any moisture.

He said: "The time needed to do this was highlighted by the team to me 12 months ago."

Glen Sannox undertook sea trials earlier this year, but in those tests the 102-metre vessel was not using LNG.