Although the global maritime industry is making significant progress in the fight to reduce ship greenhouse gases and other ship-to-air emissions, it should not lose sight of what may be going on below the waterline, members of the World Ocean Council (WOC) have been told.
At the WOC Sustainable Ocean Summit in Barcelona, Craig Carter, VP Business Development, Thordon, told the summit that there are today a number of initiatives looking at reducing emissions above the waterline, but not so many looking at preventing pollution below the waterline, which he felt should be part of UN global sustainable development goals, specifically No 14 – Life Below Water.
Carter said: “To further advance ocean sustainable development and put to sea truly zero-emissions ships, then we really do have to get rid of the oil-lubricated shaft line and replace it with one lubricated by seawater. From well to wake, the environmental impact of an oil-lubricated sterntube needs serious consideration.”
Carter estimated conservatively, based on data from several environmental sources, that leaks from the global shipping fleet’s propeller shafts resulted in more than 60m US gallons of oil polluting the world’s seas and oceans in 2021.
He said: “This is about the same as the Amoco Cadiz spill, but it’s happening year after year after year. Oil-lubricated propeller shafts are often considered to be sealed systems, but they’re not. If they were, then a ship’s oil header tank containing 2000-3000 litres of oil wouldn’t need topping up with oil every few years.”
While damaged and worn sterntube seals (as in the header image) contribute massively to the constant flow of oil into our seas and oceans, a research paper carried out last year by Linnaeus University’s Kalmar Maritime Academy concluded that sterntube seals are not at all leak free, with some oil leakage considered as ‘normal’ operating conditions. Carter went on to explain that the advancements made in elastomeric polymer materials over the last decade not only offer a viable environmental and economic alternative to the oil-based system but seawater-lubricated shaft lines can also figure in the shipping industry’s CO2 emissions abatement plans.
He added: “Initial research suggests that because a seawater-lubricated propeller shaft system operates with lower friction coefficient (resistance) compared to one operating oil-lubricated white metal bearings, less fuel is required to propel the vessel, resulting in a small but nonetheless important reduction in carbon emissions. This means it can form part of a ship manager’s CII measures, which becomes mandatory next year under MARPOL Annex VI.”
The Sustainable Ports and Shipping for the Blue Economy discussion followed keynotes from Simon Bennett, General Manager, Sustainable Development, Swire Shipping Pte Ltd., and Jordi Vila Martinez Head of Environmental Department, Autoritat Portuària De Barcelona. Other panelists were Pau Guasch, Co-Founder and General Manager, GPA SeaBots; Cristina Alexendri, COO, Bound4Blue; Ana Pinela, Senior Project Manager, Atlantic Smart Ports – Blue Acceleration Network; and Gina Panayiotou, ESG Manager, West of England. The session was moderated by Emma Cobos, Director, Innovation and Business Strategy, Port of Barcelona.
