After a Leak, Troubled Ferry Glen Sannox No Longer Runs on LNG

The Scottish ferry Glen Sannox was billed as an environmentally-friendly LNG powered alternative when it was first ordered in 2014, and the builder and the operator invested heavily in bringing its LNG fuel system online, a factor in the vessel's years-long delivery delay. But after a serious gas leak incident last year, it is no longer using the high-spec system and has switched to running on diesel, according to a new investigation by BBC. 

On June 3, 2025, Glen Sannox began a routine crossing from Troon to Brodick, Arran. During the crossing, gas alarms sounded and the port engine automatically cut out, a safety response to an abnormality in the supply of natural gas fuel. The crew switched to diesel and investigated the matter further when they reached the pier in Brodick; no serious issues were found and the vessel departed for the return journey as usual. 

Later that evening, while the vessel was under way back to Troon and running on gas once more, a high-pressure LNG vent valve failed. Over the course of 12 minutes, it released 700 kilos of gas out to the exterior of the ship through a vent pipe on the starboard side. The size of the leak and the location of the vent – just forward of a ventilation intake – meant that a small quantity of gas was drawn back inside the ship, not enough to cause harm but enough to provoke concern.

The crew did not initially recognize that a leak had occurred, and they attempted to restart an engine before they discovered the root cause of the incident. The crew had to manually close the electrically-operated valve for the return journey. That appears to have been the last time that the ship ran on LNG, and the vessel's LNG fuel tank has been empty since late last year.

The operator's internal investigation report – obtained by BBC – found that the vent valve may have been damaged through contact with a loose component, possibly linked to the ship's severe vibration issues when operating astern. It did not have a monitoring sensor or position indicator at the time; that safety function has since been retrofitted. The OEM had previously issued three service memos suggesting that the valve be upgraded or replaced, and reinstalled with extra care in order to prevent loosening of fasteners.

In a statement, operator CalMac said that it has taken remedial action and that the ship is safe to run on LNG, but has not done so for the sole reason of speeding up its return to operations. At the time, CalMac had other serious issues to contend with, notably a persistent problem with hull cracking. 

The Glen Sannox saga has had many twists and turns, and the BBC's revelation is just the latest. Shipyard Ferguson Marine started work on the CalMac ferry in 2015, went bankrupt after serious design flaws emerged, and was nationalized in 2019. After rework, budget hikes and personnel changes, the ferry finally entered service in January 2025, six years behind schedule and four times over budget. It has been repeatedly out of operation for repairs since delivery.