Sustainable Stern Tube Bearing Technology

Sustainable Stern Tube Bearing Technology

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We don’t usually consider stern tube bearings as being environmentally pleasant. However we must always.

Picture courtesy of Thordon Bearings

Jul 31, 2022 5:59 PM by

The Maritime Government

(Article initially printed in Might/June 2022 version.)

We stay in a hyper-connected, digitally targeted world.

By way of globalization and advances in expertise, we’re higher linked and have larger entry to items and companies and data than ever earlier than. So it’s simple to overlook that 90 % of every thing nonetheless travels precisely because it did 500 years in the past.

By ship.

That commerce is carried by the roughly 55,000 service provider ships that commerce internationally. Whether or not basic cargo, container or tanker, every of those is supplied with a number of propellers that drive the vessel by way of the water. The propeller in flip is linked to the engine through a shaft, and that shaft is supported by varied bearings to maintain it rotating easily.

These bearings usually require grease or oil lubrication. An oil-lubricated stern tube system was launched within the Nineteen Fifties to assist management the wear and tear lifetime of shaft bearings. One of many system’s elements is called the strict tube bearing, and its principal job is to seal the oil-filled stern tube and forestall that oil from going into the ocean and inflicting marine air pollution.

But accidents nonetheless occur.

Fishing nets, misaligned propeller shafts, poorly maintained seals or manufacturing defects can all trigger the seal to fail. The ensuing lack of oil containment might be pricey for the shipowner and result in fines and even jail time for the crew.  

Oil-lubricated stern tube techniques have been developed ostensibly to manage bearing put on life. However what if these techniques didn’t want oil in any respect?

Water-Cooled Bearings

Water-cooled bearings have the benefit of not requiring oil lubrication or EALs (environmentally acceptable lubricants), lowering the air pollution danger to zero. Whereas the shaft is spinning at velocity the water creates a wedge that utterly separates the shaft from the bearing materials, bringing the coefficient of friction to underneath 0.001. This reduces system put on to a negligible quantity.

Water additionally has twice the particular warmth of oil. An equal weight of water will soak up twice the warmth of oil lubricants, making the cooling properties far superior. By utilizing water as a lubricant, contamination seals usually are not required. If seals usually are not required, pumps and tanks is probably not mandatory. This results in an easier shaft-bearing system and rapid price financial savings within the construct part.

Stern tube bearings are designed with a sequence of lands and grooves, working longitudinally.  When a contaminant reminiscent of sand or grit enters the system, the water will wash it right into a groove the place it’s flushed out. Because of the materials development of this model of bearing, it avoids scoring the propeller shaft, not like a steel bearing, which has no give. 

Additional, a greased shaft will entice contaminants, primarily turning it right into a lapping compound.  It will repeatedly put on the shaft with each rotation. 

Water-cooled bearings have been developed utilizing probably the most trendy expertise accessible and one of many oldest sustainable sources identified to man.

Composite Bearings

Thordon Bearings, a Thompson Gordon firm, is an Ontario-based producer specializing within the manufacturing of oil-and-grease-free bearings and seals. The corporate makes use of a proprietary, grease-free, water-lubricated polymer materials. This low-coefficient bearing materials helps to cut back shaft/bearing friction and eliminates stick slip.

Thordon lately produced the biggest rudder bearing ever manufactured – in twenty-four hours, no much less!

A containership drydocked in Dubai was discovered to have rudder bearing clearances on the restrict.  With the tip of the upkeep interval quick approaching, the proprietor wanted to resolve whether or not to return to drydock or change the present steel bearing with Thordon’s water-lubricated expertise. Thordon’s native associate, Ocean Energy Worldwide, assured the shipyard it might ship the bearing on time.

With solely a rudder inventory drawing to reference, Thordon’s Burlington, Ontario-based staff solid an outsized piece with an ample security margin. The completed piece measured 1,250 mm x 1,050 mm x 1,350 mm and weighed 2,500 lbs. Whereas the biggest bearing ever delivered, it was nonetheless seven occasions lighter than a comparable bronze bearing and light-weight sufficient that it was loaded onto a industrial airliner that evening.

Twenty-four hours later the bearing arrived in Dubai the place the native staff accomplished ultimate machining to the precise specs. The piece was then supercooled utilizing liquid nitrogen, inflicting the outer diameter to shrink by 21.93 mm and permitting the bearing to be simply fitted in place.

The ensuing set up has the next abrasion resistance than the bronze bearing it changed with double the anticipated working life.

Multi-Vessel Contract

Some great benefits of water-cooled bearings paired with Thordon’s quick supply time have led to a multi-vessel settlement with Maritime Companions, the world’s largest operator of inland vessels.

Twelve twin-screw push boats are scheduled to be delivered from Louisiana-based FMT Shipyard with gear that features RiverTough tailshaft bearings, ThorPlas-Blue rudder bearings with Pucker Seals, ThorPlas-Blue steering linkage bushings, SXL thrust washers and TG100 tailshaft seals.

Working one of the trendy, new and environmentally environment friendly fleets throughout the U.S. inland river community, Maritime Companions went all-in with Thordon’s water-cooled options to make sure dependable operation and nil air pollution danger.

Wood Bearings

On the opposite finish of the spectrum is the longest working water-cooled bearing resolution in historical past: picket bearings produced from lignum vitae.

Lignum vitae has been in service for over three centuries. It obtained its first patent in 1852.  Listed in SNAME in 1882. Used all through the fleet in WW1, then once more in WW2. It was chosen to be used on the united statesNautilus – the world’s first nuclear-powered submarine. The quickest ocean liner on this planet, the SS United States, was awarded the Blue Riband for the quickest crossing of the Atlantic on its maiden voyage in 1952, a document it holds to today.  

Its shaft bearing was produced from lignum vitae.

No different bearing materials has the historical past or longevity of LV. And since it’s a completely renewable useful resource, it holds the respect of being probably the most environmentally pleasant resolution accessible.

What Makes It So Good?

Lignum vitae is the toughest of all traded woods, studying 4,390 lbf on the Janka scale – equal to aluminum. It’s additionally the densest of all hardwoods at 6.8 lb/bd ft. in contrast with ebony at 5.8 lb/bd ft. It takes centuries for one in every of these bushes to succeed in maturity. 

It has pure oils inflicting self-lubrication and wear-resistance. A examine by the U.S. Navy discovered that LV had the bottom coefficient of friction ever recorded. These oils additionally present resistance to rot and, being a wooden, it’s not inclined to break by electrolysis.

Most of those properties are the results of its distinctive mobile construction. Not like most wooden, which kinds its grains in a longitudinal sample, LV kinds as a woven matrix with a 60-degree angle of the grains. This acts like a preloaded spring. It may be compressed utilizing a 100-ton press and can spring again and regain its form with good reminiscence after a couple of days.

It’s this final property that makes it good to be used in stern tubes. The picket bearing conforms to the shaft over time, primarily lapping in, which is when the bottom coefficient is shaped. And since shaft vibration is a perform of an excessive amount of clearance, this property will nearly completely remove vibration, even with a misaligned shaft.

Fixed Growth

Bob Shortridge, the founding father of Lignum Vitae North America, is continually pushing the envelope of the fabric. He at present has his bearings present process testing by Canadian-based HydroTech, an organization specializing in bearing expertise for marine and hydroelectric industries. 

Working to develop the absolute best bearing for all circumstances, the pair are testing LV in opposition to all materials sorts and designs. Discovering a cloth that may develop the best water wedge at excessive speeds whereas limiting put on at low speeds is the final word purpose, and lignum vitae’s preliminary outcomes present it rising to the highest. 

Shortridge can be a historical past buff with a longstanding fascination with the SS United States and what made her so quick. As of this writing, he’s donating lignum vitae bearing materials for show within the SS United States Conservancy museum and awaiting permission to board the vessel to examine the strict tube bearing with the purpose of additional refining his designs.     

Making use of trendy manufacturing strategies to one of many oldest dependable supplies is a recipe for sustainable success.

When Issues Go Incorrect

Refitting or putting in bearings and seals whereas in drydock is one factor. Repairing or changing them whereas the vessel is within the water after a breakdown is one thing else fully.  

Specializing in stern seals and propulsion techniques, Aegir Marine offers a versatile strategy to ship upkeep. Whereas completely happy to match your drydock timeframe, the place it actually stands out is conducting floating and emergency underwater repairs.

Aegir’s proprietary SealDock is an underwater habitat that creates a dry working surroundings beneath the waterline. Customized-designed to suit venture necessities, SealDock makes use of a rubber sealing mechanism paired with constructive air strain. This enables its skilled technicians to entry the worksite and full the repairs.

Aegir has its Prime in-house model or alternative components manufactured at its DNV-approved services. With a world distribution community, it’s ideally positioned to get your vessel repaired, refitted and again underway.

These capabilities led to a 2022 partnership with Spliethoff to produce stern tube sealing components and companies. Working a world dry cargo fleet of over 50 vessels, Spliethoff delivers high-value cargo and requires most fleet uptime. The partnership with Aegir will assist guarantee a world provide and response for all stern tube sealing components and companies required to maintain cargo shifting.

Environmentally Pleasant Technology

Relating to progress in maritime, the mission is evident: Develop and ship environmentally sustainable options for the worldwide delivery trade. Water-cooled bearing expertise is probably the most environmentally pleasant alternative with zero danger of air pollution.  

Whether or not utilizing the most recent in polymer expertise or an historical wooden with properties nonetheless as but undiscovered, there are nice selections to get the job achieved. – MarEx 

Frequent contributor Sean Hogue is Senior Vice President of Operations at Baker Marine Options.


The opinions expressed herein are the creator’s and never essentially these of The Maritime Government.

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