Exclusive:Cause of Glen Sannox ferry hull crack revealed - and what is being done about it

Vibration in CalMac’s brand new ferry Glen Sannox may have caused the crack in its hull, the operator has told The Scotsman.

The fault in a weld seam forced the vessel out of service for two days for repairs in March, two months after being deployed on the route between Troon and Brodick in Arran.

Glen Sannox arriving in Brodick on its first official passenger sailing on January 13. Picture: John Devlin | John Devlin/The Scotsman

CalMac said the 130mm (5in) “minor” defect close to the waterline included a 25mm (1in) section that had let in a “very small amount of water”.

Holes were drilled at each end of the crack to prevent it expanding and the seam was re-welded.

Scotland’s transport links are the lifeblood of the nation - subscribe today to our Transport newsletter

The Scottish Government firm, which is Britain’s biggest ferry operator, said the defect was on the starboard [right] side of a machinery space near the starboard rudder.

The ferry, which is CalMac’s second largest with space for more than 850 passengers, was completed six-and-a-half years late in November by the Ferguson Marine shipyard.

A CalMac spokeswoman said: “Investigations have so far discovered vibration in this particular area of Glen Sannox, which may have caused the seam to crack.

“Mitigations are now in place for the vibration, which only occurs near where the crack appeared.

“Further investigation into the root cause of the vibration is underway and CalMac, [Scottish Government ferry owning firm] Caledonian Maritime Assets Limited (Cmal) and Ferguson Marine are working together on this.

“It is not uncommon to have an issue like this as a new vessel is brought into regular service.”

CalMac has said such minor weld defects had been found in some of its other ferries, but none were in the three smaller vessels built by Ferguson Marine in the 2010s.

Ferguson Marine chief financial officer David Dishon said in March: “The welding on Glen Sannox was subject to rigorous checks at various points throughout the build and was signed off prior to handover by both Lloyds Register and Cmal.

“The quality of the welding and fabrication by the Ferguson’s workforce was praised by Cmal in its inspections of the vessel during the construction process.

“We are extremely proud of the quality of work we delivered on this and other vessels.”

The fault forced the cancellation of sailings between Troon and Brodick in Arran, one of the company’s busiest routes, when initially discovered. It came after the Glen Sannox was taken out of service for a week in February to replace parts in the anchor system.

At the time the weld seam crack was revealed, Scottish Conservatives transport spokesperson Sue Webber described the fault as a “hammer blow” to passengers, whom she said had been “betrayed at every turn” by the Scottish Government.

“After waiting nearly seven years for this massively overbudget vessel, island communities will be dismayed that it’s broken down within weeks of its launch,” she said last month. “The SNP’s failure to provide a viable ferry network has left passengers stranded once again.”

The Ferguson Marine yard has come under intense scrutiny due to the delayed and over-budget Arran ferries Glen Sannox and Glen Rosa – the overall cost of which is approaching four times the initial figure of £97 million.