Providing zero-emissions below the waterline, water-lubricated bearings are making inroads on newbuilds with technical equivalence of oil-lubricated systems
Water-lubricated bearings do offer a more ecologically acceptable option than the standard oil-lubricated products in both newbuilds and retrofits, according to speakers at a recent webinar.
Sponsored by Canada’s Thordon Bearings, the Riviera webinar, entitled Seals and Bearings: is it time to consider water-lubricated bearings?, highlighted the growing application of water-lubricated bearings across a variety of vessel types, including cruise ships, for more than 20 years as an increasingly reliable solution that removes the risk of oil leaks.
As Thordon’s regional manager EMEA-ANZ George Morrison noted in his presentation, the group first started supplying Navy and coastguard vessels before achieving a major breakthrough commercial marine application in 1998 with Carnival’s Grand Princess.
Fitted with water-lubricated bearings in its propeller shaft lines in 1998, the cruise ship went on to 21 years of trouble-free operation before the bearings were replaced during docking.
“We’re very proud that there are now more than 50 cruise ships with our bearings that, up to the start of the pandemic, had been operating without one day lost or one port of call missed due to a problem with our equipment,” Mr Morrison said. “[These bearings] provide a solution that guarantees zero-emissions below the waterline [and] they are cheaper to operate with the same, if not better, reliability than an oil-lubricated system.” He added that a typical stern tube propeller shaft system contains 1,500 to 3,000 litres of mineral oil.
Also, he explained, some five years ago class societies boosted the case for water-lubricated bearings, adopting rules that broadly provided technical equivalence between them and oil-lubricated systems.
“A seawater-lubricated propeller shaft bearing system is the only system that lowers operational costs, guarantees compliance and has zero emissions below the waterline,” he concluded in an opening summary.
More data on oil leakage
However, while agreeing on the importance of cleaner oceans and environmentally compliant ships, fellow panellist Donald Gregory, technical director Gulf Marine Oil, questioned the shortage of data on oil leakages that might justify the use of water-lubricated bearings. “We need to be more science and fact based,” he said, citing the importance of making a business case that would convince shipyards to consider alternatives. “Is the shipping industry receiving the right signals and rewards from class societies and regulators to develop tomorrow’s solutions?”
“Shipyards are used to producing standard ships with oil-lubricated systems”
Similarly, proving the vessel operator perspective, panellist Caroline Huot, senior vice-president for ship management with Delta Corporation Shipping, emphasised the necessity of benefits outweighing costs in installing water-lubricated bearings over the less expensive and standard alternative. This was especially true in the case of retrofits, when the existing fleet was struggling financially.
“Is there a way to transition from oil lubrication into water lubrication?” she asked, referring to the cost and complexity of retrofitting. Also, she pointed out that shipyards are extremely conservative and prefer to focus on keeping down costs by using standard equipment, often sourced from local suppliers.
“Shipyards are one of the big challenges we have,” agreed Mr Morrison. “They are used to producing standard ships with oil-lubricated systems,” he said, suggesting there was “an unholy alliance” between shipyards and the oil lubricant industry, with the latter supplying seals and bearings at costs.
“It means that the shipowner is paying money through the life of the vessel to have the seals repaired,” he said.
Yet, as he added, it was clear that water-lubricated bearings are beginning to make inroads, particularly in newbuilds. In recent years they have been installed on a wide variety of vessels including offshore supply ships, container and feeder ships, ferries and oil tankers.
Making an argument for oil-lubricated bearings, especially in shaft lines, Mr Gregory pointed out that mineral oil is a highly effective lubricant. That may not however be the case with water, although it is an effective lubricant for certain applications. Petroleum-sourced lubricants were perfect lubricants for most applications on board ship. “And there has been no historic evidence that leakages have been widespread,” he noted.
Also, the design and manufacture of seals has improved. “In a [foil] stern tube sealing system, there are now seals which are totally leak-proof in normal operations,” Mr Gregory said. “Leaks can only take place if there is some sort of accident or other failure. With a modern system, the amount of leakage into the sea is very substantially reduced. It is almost zero.”
Gulf Oil’s technical director also argued that product development in merchant shipping is lagging. “[It] has declined or is in retreat,” he said. “And there has been a paucity of new ideas applied to the conventional stern tube.” The industry should look elsewhere for innovation, for instance to industrial applications “that have better solutions that can be transferred to the merchant ship.”
Overall, though, he stressed that regulation “must be based on smart goals and not on prescription [while also] seeking to incentivise development by rewarding aspiration and achievements.”
Mr Gregory also referred to the improving quality of bearings produced by industry, including ones that do not even require lubrication. “But the shipping industry does not seem to be moving along in that direction. It all seems to be driven by cost. I think this needs to change if we are going to advance,” he said in response to an attendee’s question. And looking to the future, citing the fact that scientists have just achieved a landing on Mars, it would not surprise him if industry came up with a zero-leakage for stern tube sealing systems. While conceding that seals have improved greatly in the last 50 years, Mr Morrison thought a zero-leakage seal was as improbable as a friction-free bearing.
“When you look at water lubrication, is the cost-benefit sufficient?”
As Ms Huot also pointed out, environmentally acceptable lubricants are biodegradable. “They would not affect the marine environment in the short or long term, so the question is: when you look at water lubrication, is the cost-benefit sufficient?”
Thordon, said Mr Morrison, was happy that “EALs are on the agenda because that is the environmental message we want to be part of.”
Ms Huot also raised the issue of how best to monitor the condition of the shaft line, in view of the fact that it is one of the most important elements for safe navigation. “From a shipowner’s point of view, that is the question I would ask if I was to consider adopting such a technology,” she said.
Meantime, Thordon is developing a new concept of an inspection space for the shaft line in the stern tube, a concept that rang a bell with Mr Gregory. “One of the problems with the stern tube is its inaccessibility,” he said. “That is a brilliant idea, but how do we make shipyards consider putting something like that into a vessel? As soon as you have access you have a totally different scenario. You can oil lubricate or you can water lubricate. You have the choices.”
However, it was vital to understand exactly what kind of problems the shipping industry was trying to solve – “if we take a singularity view and say we are just trying to solve oil leakage, we miss a lot,” he said.
Looking forward, he argued for shipowners taking more responsibility over leakages and emissions. “Or do they just want to make profits and not be accountable,” he said, pointing out that the shipowners used to have naval architect departments that influenced these decisions. It was important that the shipping industry was driven less by cost and more by environmental considerations – “I think this needs to change if we’re going to advance.”
Responding to considerable interest from attendees about pressure from the rising wave of ESG-minded investors to use systems such as water-lubricated bearings, Ms Huot pointed out how most charterers and other shipowners are moving in a more sustainable direction. “Water lubrication is definitely an option in that sense. It is a signal,” she said. “But for me it does not look like an utmost priority, considering the number of pressures and changes that are happening right now in ship design that are imposed by regulation, or driven by environmental protection.” It was better for shipowners to look at integrated solutions rather than just one technology, she suggested.
Asked about dealing with marine growth in bearings, Mr Morrison distinguished between organic marine growth and a relatively recent phenomenon, calcification as a result of galvanic action. “If the vessel is used regularly, as in the case of cruise ships because they never stop, then none of these growths has a chance to form on the bearing surfaces,” he explained. However, growth can occur when a ship is out of action for a long period, like Navy ships. “We recommend a maintenance schedule whereby the shafts are turned once, twice or three times a week,” he said.
In a telling point, Mr Morrison stressed the risk of faulty stern tube bearings. “People tend to be very sensitive about stern tube bearings because it is probably the one part of the ship that has one of the lowest values but carries the biggest risk. Its value to risk profile is really quite considerable.”