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Study makes case for seawater lubricated propeller shaft bearings

Written by Nick Blenkey
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Twin screw vessel in dry dock

SEPTEMBER 6, 2018 — A new study highlights the commercial and environmental benefits of seawater lubricated propeller shaft bearing arrangements. Published by Thordon Bearings, it indicates that substantial operational savings can be made by switching from oil lubricated shafts.

The study, the findings of which were presented for the first time during the SMM 2018 trade fair in Hamburg, Germany, was carried out in response to the increase in oil and oil-based Environmentally Acceptable Lubricant (EAL) lubricated stern tube bearing failures, which are placing an additional and unnecessary financial burden on shipowners.

“It is quite staggering that over 95% of all new commercial ships continue to be built with oil lubricated propeller shafts – a system that is not only operationally expensive but environmentally questionable,” said Craig Carter, Thordon Bearing’s Director of Marketing and Customer Service.

Thordon’s 14 page study, called “Our Future, Our Ocean,” presents the case for water lubrication to shipowners and shipbuilders as a commercially and technically viable way of increasing profits while achieving corporate sustainability goals.”

The 14-page document explains that while the low capital expenditure of an oil-lubricated system is an obvious attraction, any financial advantage is lost once the vessel enters the water, due to the costs associated with purchasing lubricating oils, regular maintenance and unscheduled drydockings required to repair or replace faulty shaft seals.

While emergency seal repairs alone can cost anywhere from $150,000 to $300,000, excluding drydock costs, the paper states that the constant topping up of an oil-lubricated system, combined with the regularity of aft seal failure, can cost shipowners in excess of $6.5 billion over a twenty-five-year period.

The paper reveals that for a typical single screw bulk carrier turning a 650mm shaft, the total cost of operating an oil-lubricated system over 25 years (including capital investment) is $605,925 against $370,000 for a seawater-lubricated arrangement.

Although part of the cost of operating an oil-lubricated system is dependent on oil price fluctuations and does not take into account the use of more expensive EALs, the use of seawater as the lubricating medium is obviously free of cost.

“While the environmental impact of oil leaking from stern tubes has been well documented, the commercial impact on the shipowners bottom line has not been addressed. This study intends to raise awareness of the commercial disadvantages from the continued use of oil lubricated propeller shaft bearing systems, while offering a more cost-effective and more environmentally acceptable solution,” said Carter.

Download “Our Future, Our Ocean” HERE


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