700kg LNG Leak Forces Scotland’s Flagship Ferry Off Green Fuel
Scotland’s troubled Glen Sannox ferry has been running on diesel since a 700kg LNG leak last year exposed safety flaws.
The Glen Sannox, a Scottish ferry once hailed as a pioneer for its liquefied natural gas (LNG) propulsion system, has abandoned its cleaner fuel after a serious gas leak last year. The vessel, operated by CalMac, was designed to cut emissions by using LNG instead of traditional marine diesel, but a June 2025 incident exposed critical flaws in its fuel system.
During a routine crossing from Troon to Brodick on June 3, 2025, gas alarms sounded and the ferry’s port engine shut down automatically. The crew switched to diesel and completed the voyage, but later that evening, a high-pressure LNG vent valve failed. Over 12 minutes, the valve released 700 kilograms of gas—enough to fill a four-bedroom house—through a vent pipe on the ship’s starboard side. Some gas was drawn back into the vessel through a ventilation intake, though not in quantities that posed immediate harm.
Safety failure forces switch to diesel: Ferry
The crew initially failed to detect the leak and attempted to restart an engine before manually closing the faulty valve. An internal investigation by CalMac, obtained by the BBC, revealed the valve may have been damaged by a loose component, possibly linked to the ferry’s severe vibration issues when operating in reverse.
Natural Gas
The valve also lacked a monitoring sensor or position indicator at the time, a safety gap later addressed through retrofitting. The original equipment manufacturer had previously issued three service memos recommending upgrades or replacements, but these warnings went unheeded.
Since the incident, the Glen Sannox has run exclusively on diesel, and its LNG fuel tank has remained empty. CalMac stated the vessel is now safe to operate on LNG but has prioritized returning it to service quickly, citing other pressing issues such as persistent hull cracking.
The Glen Sannox has been plagued by problems since its inception. Ordered in 2014 as an eco-friendly alternative, the ferry was delivered in January 2025—six years behind schedule and four times over its original £97 million budget. The project’s troubles began when builder Ferguson Marine, which started construction in 2015, went bankrupt in 2019 after design flaws emerged. The Scottish government nationalized the shipyard to complete the vessel, but the ferry has since faced repeated outages for repairs.
Delays, cost overruns, and political fallout
The gas leak revelation has also triggered political backlash. Transport Secretary Stephen Flynn faced criticism after admitting he was unaware of the incident, telling a parliamentary committee he had missed the BBC’s report because he was “Facetiming my kids.” Opposition politicians condemned the delay in public disclosure, with Willie Rennie, convenor of the transport committee, calling the incident “significant” and questioning the government’s transparency.
For now, the Glen Sannox remains a cautionary tale about the challenges of adopting new maritime technologies. While Scotland continues to push for greener ferry fleets, the incident underscores the need for rigorous safety measures and clear communication when introducing untested systems. Passengers traveling between Troon and Brodick are advised to monitor CalMac’s service updates for any operational changes.
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