Trials of the liquified natural gas (LNG) system on the delayed ferry Glen Sannox have been postponed as it is taking longer than expected to load the fuel onboard.

With the deadline for handover 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.

The Scotsman reported 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 shipyard dealing with these issues over the past year.

MV Glen Rosa is launched at Ferguson Marine Port Glasgow shipyardMV Glen Rosa is launched at Ferguson Marine Port Glasgow shipyard (Image: Jane Barlow/PA)

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.”

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MV Glen Rosa on the ClydeMV Glen Rosa on the Clyde (Image: Jane Barlow/PA)

Ferguson Marine said it is working with the ferry owning agency CMAL and the Scottish Government “to assess what impact this week’s delays may have on handover” – which is currently scheduled for September 30 at the latest.

Following the harbour trials, the vessel will be put through its paces at sea, stopping and starting several times and carrying out endurance tests.

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 £97 million price tag.

David Tydeman, who was chief executive of Ferguson Marine until March, told the newspaper 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.

A Scottish Government spokesperson said: “It is disappointing to learn of challenges and a further delay to handover during these later stages of commissioning the complex LNG system on Glen Sannox.

“The Scottish Government is focused on working closely with Ferguson Marine and delivery partners during this phase of the programme and to ensure that all possible risks which could impact further on handover are minimised.

“The Deputy First Minister has made clear to Ferguson Marine the importance of the two ferries entering service as soon as possible so that they can deliver a high quality service to our island communities.”