According to UK media reports, the ro-pax vessel ‘Glen Sannox’ will, once it enters service in January 2025, have higher GHG emissions than the 30-plus year old ferry it replaces.
The CalMac vessel, which was subject to long delays in its delivery from Ferguson Marine, has been estimated to emit just over 10,000t CO2e per year, compared to the 7,700t from the Caledonian Isles, which it replaces on the route to the Isle of Arran. Glen Sannox has capacity for 852 passengers and 127 cars, compared to the 90 cars and 1000 passengers of its predecessor. Shipowner CMAL points out that the emissions figure is misleading, as the new ship is larger, while emissions of SOx and NOx are substantially lower. The higher power and manoeuvrability should mean fewer weather-related cancellations.
However, other spokespeople quoted by BBC News say that if importing the LNG fuel from Qatar to the terminal in Kent, and transporting it from there by road to Scotland (there is no suitable LNG terminal nearer) is factored in, it would be cheaper and greener to run the ship on MGO.
The discrepancy is largely due to methane slip, which, when Glen Sannox was ordered in 2015, was not seen as such a problem in terms of GHG. Later engine designs have cut methane slip, while the emphasis for short-distance ferry propulsion has switched to pure electric or battery-hybrid power. CalMac and CMAL have expressed interest in such systems for future vessels. But the charging facilities would depend on costly infrastructure upgrades, although there is a supply of renewable electricity.
CMAL is reported as saying that LNG was the best option at the time of ordering for Glen Sannox and sister vessel Glen Rosa, the larger sizes of which reflect increased numbers of vehicles as well as the larger sizes of current vehicles.
If bio-gas could be used instead of imported LNG, the well-to-wake emissions could be far lower. Scotland has possibilities for manufacturing bio-methane from organic waste including whisky distilling by-products. But no such biogas plant exists in Scotland, and building one would require major capital investment including the necessary liquefaction plant.
Some lessons have been learned; four new large CalMac ferries in build in Turkey will have MGO engines with battery power for manoeuvring in port, and are designed for future alternative fuel operation, and more efficient hull shapes are possible without the draught limitations of the Arran route.
It has also been pointed out that a chartered-in catamaran ferry, with 98-car capacity, which has been operating on the Arran route pending the arrival of Glen Sannox, has proved less costly, far more fuel-efficient and cleaner than the LNG-fuelled vessels, despite running on MGO.
Image: ‘Glen Sannox’ on sea trials (source: Ferguson Marine)
