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HANSA 11-2022

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SCHIFFSTECHNIK | SHIP

SCHIFFSTECHNIK | SHIP TECHNOLOGY Fuel savings from bow to propeller shaft While 95 % of the world merchant fleet use traditional oil lubricated metal bearings in their propeller shaft setup, new research shows a significant fuel savings potential of water lubricated polymer bearings With the International Maritime Organization’s Carbon Intensity Indicator (CII) regulation coming into force in January 2023, the focus is now heavily on ship efficiency. More efficient hull designs and propellers as well as modern engine technology and digital solutions are in use to reduce ships’ fuel consumption and thus CO 2 emissions. Propeller shaft bearings have not been on top of the ship efficiency agenda yet, but peer-reviewed research by Thordon Bearings into the hydrodynamic lubrication efficiency of a ship’s propeller shaft bearing has found that the use of seawater-lubricated elastomeric polymer bearings reduces fuel consumption, and, consequently, carbon emissions. Seawater-lubricated propeller shaft bearings have long been promoted as environmentally friendly as no oil can ever leak into the water as is the case for traditional oil-lubricated white metal propeller shaft bearings, where seals and bearings are frequently damaged, leaking millions of gallons of oil into the sea every year. »A polymer bearing is an open system that is flushed with seawater constantly,« explains Elena Corin, Senior Manager, Special Marine Projects, Thordon Bearings. No oil means no environmental hazard and of course lower OPEX and reduced maintenance – so far, so good. The new findings that Thordon presented in early September, however, are the first indication that the arrangement reduces hydrodynamic resistance enough to improve fuel consumption. The research is based on a new methodology for calculating the performance of seawater-lubricated bearings, which, until now, has been based on decades-old theory developed for oil-lubricated propeller shaft bearings. »A classic bearing theory is valid and commonly used for oillubricated metal bearings. However, two major factors of seawater-lubricated bearings, namely low lubricant viscosity and deformability of the polymer bearing surface, make the application of rigid surface bearing calculations susceptible,« says Thordon Bearings’ Chief Research Engineer, Gary Ren. Less fuel, lower life cycle costs Essentially, a propeller shaft lubricated by oil has a higher viscosity than water meaning more energy is required to turn the shaft. Ren’s method considers the characteristics of seawater as a lubricant, the polymer materials used, bearing pressures, viscosity, friction, and other parameters. Test results confirmed that fuel losses due to the friction coefficient of an oil-lubricated propeller shaft bearing system can be significantly reduced by using seawater-lubricated polymer bearings. Ren says that fuel losses due to the friction coefficient (hydrodynamic resistance) of an oil-lubricated propeller shaft bearing system can be reduced by as much as 85 %. Thordon Bearings used the methodology to compare the fuel consumption of a 3,400 TEU Panamax containership and an Aframax tanker operating a 640 mm diameter oil-lubricated propeller shaft bearing versus the same ships operating Thordon’s open COM- PAC seawater-lubricated bearing system. Each vessel was assumed to run on VLSFO (very low sulphur fuel oil) at a global average price of 890 $/t, operating for 70 % of the time. »Fuel costs will depend on the operational profile of the vessel, but we conservatively estimate annual savings of at least 10,000 $ per vessel, said Corin. This is in addition to the other life cycle cost savings associated with a Thordon seawater-lubricated bearing system.« Apart from the current fuel and energy crisis, fuel efficiency is also coming to the fore due to the IMO’s Carbon Intensity Indicator (CII) regulation. From January 1st, 2023, shipowners will be required to document their Attained Annual CII and verify it against the Required Annual CII to determine their vessels’ operational carbon intensity rating. Savings in fuel consumption and subsequent reduction of CO 2 emissions are the focus of the CII measure. This is an area were the Canadian company sees another advantage for its technology. Thordon Bearings is currently carrying out research to assess the carbon emissions reduction attributes of vessels using a seawater-lubricated system to help shipowners meet CII requirements. With From project conception to decommissioning, bridge the gap with RINA. Visit us at Posidonia - booth 3.211 Hall 3 Make it sure, make it simple. rina.org 48 HANSA – International Maritime Journal 11 | 2022

SCHIFFSTECHNIK | SHIP TECHNOLOGY The combination of seawater and elastomerix polymer bearings reduces the friction coefficient, which leads to lower fuel consumption © Thordon Bearings the new CII measure in sight, Corin says that interest in the seawater-lubricated system is growing significantly. »There is clear increase in enquiries by owners, but also from the shipyard side,« she says. The seawater-lubricated polymer bearings are particularly interesting for newbuilds, Corin thinks. The main hurdle she sees in the standard designs that the large shipyards in Asia are using which traditionally feature oil-lubricated bearing systems. While the costs for acquisition and installation of the seawaterlubricated system are initially higher than those for oil-lubricated systems, the cost of ownership is significantly lower. Specifically, more robust bearings less prone to wear together with fewer components, less time in drydock for emergency repair, and the zero need for purchasing and storing prop shaft lubricating oil make the water lubricated system a very commercially beneficial proposition. Based on the results of case study of a Chinese shipowner running a container ship operating Thordon’s Compac system, the seawater-lubricated system would save almost 40% of the overall 25-year life cycle cost, reducing the total cost of ownership considerably. The Compac system could also be retrofitted to existing vessels, but Corin says this must be assessed on a case-by-case basis. She likes to put the focus on newbuildings that could also benefit from a seawater-lubricated propeller shaft setup in terms of the IMO’s Energy Efficiency Design Index (EEDI) that applies to new ships. fs Your one stop shop Navigation and communication equipment Alphatron Marine Deutschland | +49 (0)4101 3771 0 | sales@alphatron.de HANSA – International | Maritime alphatronmarine.com/de Journal 11 | 2022 49

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