The LNG Detour: What Scotland’s New Ferry Teaches US

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Scotland’s Glen Sannox was launched with fanfare because the nation’s first “inexperienced” ferry, meant to scale back the influence of crossings between the mainland and Arran. It was designed as a dual-fuel vessel, operating on both marine diesel or liquefied pure fuel, with the promise of cleaner air and decrease emissions. LNG was meant to chop sulfur and nitrogen oxides, enhancing native air high quality round ports and coastal communities. On the local weather aspect, it was anticipated to ship measurable carbon financial savings in comparison with the older diesel ferry it will substitute. As a substitute, it has develop into a case examine in how assumptions and design decisions can flip a well-intentioned venture right into a step backwards.

The Glen Sannox story is stretched throughout a decade. The order was positioned in 2015 with Ferguson Marine, alongside its sister ship Glen Rosa, to switch getting older diesel ferries on the Arran route. Delays in building pushed the venture far past its unique schedule, with prices rising steeply as technical and contractual issues piled up. The vessel lastly entered passenger service in January 2025, ten years after being commissioned. A yr earlier, in January 2024, the ICCT launched its Fugitive and Unburned Methane Emissions from Ships (FUMES) examine, offering contemporary proof that methane slip from LNG engines was a lot larger than trade estimates. That coincidence sharpened the scrutiny of Glen Sannox, inserting its local weather efficiency below a harsher highlight simply because it started common operations.

Protection of Glen Sannox’s emissions facilities on CalMac’s personal evaluation that put the LNG ferry at about 10,391 tons CO2e per yr versus 7,732 tons for the older Caledonian Isles, a spot of roughly 35%. These totals included LNG delivered by street tankers and methane slip. The underlying Annex A assumptions set weekly LNG burn for the primary engines and auxiliaries and used about 1.296 tons of methane slip per week, which critics say is low relative to measurement literature.

Naval architect Euan Haig’s submissions to the Scottish Parliament questioned how methane’s time profile and decay have been handled and argued that incomplete dealing with of boil-off and slip understates warming. The ICCT’s FUMES venture added weight to these considerations by reporting common methane slip of 6.4% for low-pressure dual-fuel four-stroke engines, the identical class aboard Glen Sannox, which might roughly double the slip in comparison with the Annex A enter and carry weekly and annual CO2e.

CalMac and CMAL didn’t dispute the headline annual totals however mentioned easy comparisons are deceptive as a result of Glen Sannox is bigger, sails an extended interim route from Troon as a substitute of Ardrossan, and was designed when LNG was seen as an inexpensive transition alternative. The result’s an unresolved hole between measurement-based slip charges and the operator’s assumed slip that materially impacts the ferry’s reported local weather footprint. The mixture led me to run some numbers myself.

The comparability vessel is the Caledonian Isles, which has linked Ardrossan and Brodick since 1993. That ferry carried as much as 1,000 passengers and about 110 automobiles, consuming slightly below 3 million liters of marine diesel annually. Unfold throughout a typical yr, that interprets to about 176 tons of CO2e per week, or 132 kilograms per nautical mile of service, when operating its core timetable of 5 sailings in every course per day. The Caledonian Isles was not environment friendly by trendy requirements, however it supplied frequent and dependable service with a identified emissions profile.

Glen Sannox is bigger in some methods, with about 646 meters of auto lanes and capability for no less than 127 automobiles or 16 heavy vehicles, although its passenger load was capped at 852 after security evaluations. It was meant to function from Ardrossan as nicely, however harbor constraints compelled it to shift to Troon, stretching the crossing from 55 minutes to 75 minutes. That shift lower the attainable each day return journeys from ten to 6. In follow, this implies fewer sailings for the group and extra emissions per passenger or automobile served. The bigger ship is working tougher, however not essentially serving extra individuals.

The issue is not only the schedule. It’s the nature of LNG itself. Burning methane produces much less CO2 per unit of power than diesel, however LNG engines don’t combust all of it. Some methane escapes unburned from the cylinders and the exhaust, a phenomenon known as methane slip. Methane is a much more highly effective greenhouse fuel than CO2 over 20 and 100 yr timeframes, so even small percentages of slip can tip the stability. The Scottish Authorities’s Annex A report on Glen Sannox, revealed in early January 2024, assumed methane slip of about 1.3 tons per week. That determine was accepted as affordable till the Worldwide Council on Clear Transportation’s FUMES examine revealed measured information two weeks later. Their researchers discovered that low-pressure dual-fuel four-stroke engines, the identical household put in in Glen Sannox, slipped a mean of 6.4% of methane, practically double the optimistic estimates.

That single adjustment adjustments the local weather ledger. Glen Sannox burns about 44.5 tons of LNG per week in its predominant engines and turbines, producing about 122 tons of CO2. In case you assume 1.3 tons of methane slip, that provides 35 tons CO2e on a 100 yr foundation or 105 tons on a 20 yr foundation. Complete emissions land at 157 tons CO2e per week on the long run metric or 228 tons on the quick time period. In comparison with Caledonian Isles’ 176 tons, Glen Sannox appears barely higher on the 100 yr view and worse on the 20 yr view. However should you apply the FUMES common of 6.4% methane slip, the image shifts additional. That might imply 2.85 tons of methane escaping every week. At 27 instances the warming impact of CO2 over 100 years, that provides about 77 tons CO2e, pushing whole weekly emissions to 199 tons. On the 20 yr horizon, the methane is value 231 tons CO2e, making the ferry’s weekly whole over 353 tons. That’s greater than double the predecessor’s emissions for a similar distance traveled.

When considered per nautical mile, the previous diesel ferry produced about 132 kilograms of CO2e. Glen Sannox below its official assumptions ranges from 118 to 171 kilograms per mile, relying on whether or not you select 100 or 20 yr timeframes. Below FUMES based mostly assumptions, the vary is 150 to 266 kilograms per mile. In different phrases, utilizing extra sensible slip information makes the LNG ferry clearly worse on a long run foundation, and disastrous on a brief time period one. LNG has improved native air high quality by lowering sulfur and nitrogen oxides, however at the price of larger greenhouse fuel emissions. For a venture that was supposed to steer Scotland towards decrease carbon delivery, this can be a sobering reversal.

Glen Sannox is just not an outlier within the LNG story. Throughout the maritime sector, LNG has been marketed as a transitional gas that balances price, compliance, and sustainability. But unbiased research preserve discovering that the advantages are overstated when methane slip and provide chain emissions are included. Upstream leakage throughout extraction, processing, and liquefaction of pure fuel provides one other layer of warming that’s not seen on the smokestack. Homeowners and operators are discovering that what appeared good on a slim regulatory measure doesn’t maintain up below full lifecycle accounting. Worse, each greenback invested in LNG bunkering and dual-fuel engines is cash not spent on applied sciences that may really meet local weather targets.

In the meantime, the totally electrical finish of the market is scaling to major-route distances. Buquebus’s 130 m China Zorrilla is ready for the Buenos Aires–Colonia hall, a roughly 27–32 nautical mile crossing, carrying about 2,100 passengers and 225 automobiles on a battery pack simply over 40 MWh with charging at each terminals. Finland’s Viking Line is advancing the Helios all-electric idea for the 43 nautical mile Helsinki–Tallinn run, pairing a 195 m hull, about 2,000 passengers, roughly 2,000 lane meters, and an 85–100 MWh battery financial institution with frequent terminal charging. On the Pacific coast, BC Ferries’ new main hybrid-electric vessels are being procured to function totally electrical as soon as shore energy is in place on its busiest corridors, together with about 24 nautical miles on Tsawwassen–Swartz Bay and about 30 nautical miles on Horseshoe Bay–Departure Bay, distances squarely inside right this moment’s battery-ferry envelope with megawatt-scale quick charging.

The lesson is evident. Expertise decisions can’t be judged on tailpipe emissions alone. For delivery, actual sustainability will come from a mix of electrification on quick routes, superior biofuels the place power density is required, and finally broader adoption of zero carbon fuels the place they make financial sense. LNG was offered as a bridge, however in follow it’s a detour. Glen Sannox exhibits how ambition and intent could be undone by counting on optimistic assumptions as a substitute of empirical information. The FUMES examine is a reminder that actual measurements matter, and that insurance policies and investments needs to be grounded in noticed efficiency, not advertising claims.