Carter: A zero-emission ship must get rid of the oil-lubricated shaft

Porpeller shaft
Fishing net or rope that wraps around the propeller shaft damaging the seals allowing oil emissions to the sea; Image credit: Thordon Bearings

To further advance ocean sustainable development and put to sea truly zero-emissions ships, the shipping industry has to get rid of the oil-lubricated shaft line and replace it with one lubricated by seawater, according to Thordon Bearings’ Craig Carter.

Speaking in Barcelona on the first day of the World Ocean Council’s (WOC) Sustainable Ocean Summit, Thordon’s Vice-President of Business Development said the industry should not lose sight of what is happening below the waterline as considerable focus has been put on the ship-to-air emissions.

“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. This can be part of global policies to improve our oceans and seas under the United Nations’ Sustainable Development Goals, Number 14 – Life Below Water.”

“From well to wake, the environmental impact of an oil-lubricated sterntube needs serious consideration,” he noted.

Citing numerous environmental data sources, Carter said that conservative estimates indicate that leaks from the global shipping fleet’s propeller shafts resulted last year in more than 60 million gallons of oil polluting the world’s seas and oceans.

For example, 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 oil leakage considered “normal” operating conditions, he noted.

This is about the same as the Amoco Cadiz spill, but it’s happening year after year after year,” he said. “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!”

There are several reasons causing these types of leaks, but predominantly they result from damages to the seals caused by fishing lines pulled into seals, sand and other impurities as well as insufficient lubrication.

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.

“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 Carbon Intensity Indicator (CII) measures, which becomes mandatory next year under MARPOL Annex VI.”

“We don’t need futuristic solutions to make shipping sustainable and there’s much more than alternative fuels,” Christina Alexandri, COO of bound4blue said at the panel.

These include solutions such as having robots designed for the oceans to analyze and restore the marine environment, using suction sails to propel ships, and building collaborative innovation platforms to boost demonstrators.

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.