This past April, Princess Cruise Lines was slapped with a record penalty of $40 million for illegally dumping oily waste from cruise ships and falsifying official logs.
Glamorous cruisers and cavernous cargo ships alike are subject to regulations that limit discharges of oil into aqueous environments. The United States Environmental Protection Agencys Vessel General Permit regulates discharges incidental to the normal operation of commercial vessels in U.S. territorial waters and the Great Lakes. The VGP includes specific requirements for products used to lubricate stern tubes and other equipment that may be immersed in or in contact with seawater, referred to as oil-to-water or oil-to-sea interfaces.
As regulations like the VGP and others around the world have come into effect, the lubricants industry has responded with new lubricating oils and greases to enable ship owners to comply. While almost half-45 percent, says Grand View Research-of the marine lube market is engine oils, there continue to be significant developments in specialized marine lubricants and hardware alike, including stern tube lubrication systems.
According to Craig Carter, director of marketing for Thordon Bearings Inc. in Burlington, Ontario, around 95 percent of commercial ships are driven by one or more propellers. Each propeller is attached to a carbon steel shaft that is connected to a power source, typically a marine diesel engine, inside the hull of the vessel. The shaft is housed in a stern tube, which extends from the engine to the propeller through a carefully engineered opening in the hull under the vessels waterline. Two sets of journal bearings inside the stern tube support the propeller shaft and allow it to rotate efficiently.
In the 1950s, Carter explained, new seal technology was developed for propeller shafts. Lip seals made of elastomer with bronze housings made it possible to use mineral oil-based lubricants and metal bearings to support the propeller shaft. At both ends of a stern tube, lip seals prevent loss of lubricant as well as seawater ingress. But each seal is designed to allow a nominal amount of oil to lubricate the lips so the propeller shaft can rotate within the seal. This leads to amounts of lube continually escaping into aqueous environments as part of normal operational consumption. Additional lubricant may be released into the water as seals undergo wear or are damaged when propeller shafts entangle with fishing nets, ropes or other hazards.
A 2009 analysis of in-port lubricant discharges and leakages from vessels visiting over 4,700 ports across the globe indicated that between 4.6 million and 28.6 million liters of lubricating oil leaked each year from stern tubes alone. Dagmar Schmidt Ektin of Environmental Research Consulting, who conducted the study, estimated that vessels spent three times as many days at sea as in port. Assuming comparable leakage rates at sea as in port, total stern tube lubricant losses would be between 20 million and 120 million liters per year.
To reduce the environmental impact of lubricant discharge from stern tubes and other oil-to-sea interfaces, the VGP stipulates use of environmentally acceptable lubricants in such equipment. To qualify as an EAL, a product must satisfy EPA standards for biodegradability, minimal toxicity and bioaccumulation.
In general, EALs have been formulated with base oils made from esters, polyalkylene glycols, or blends of esters and polyalphaolefins. A recent white paper from Munich, Germany-headquartered Kluber Lubrication recommends ester-based formulations for VGP lubricant applications. According to Kluber, ester-based oils exhibit excellent biodegradation, non-bioaccumulation and low-toxicity characteristics. Operationally, they tolerate a wide range of temperatures and have high viscosity, lubricity, corrosion protection and oxidative stability properties. The paper emphasized the compatibility of many esters and seal materials.
The white paper explains that two principal types of esters are used in VGP-compliant lubricant formulations: triglycerides from vegetable or animal sources, and synthetic esters produced in chemical manufacturing processes. Because triglyceride esters tend to break down through oxidation at high temperatures and through hydrolysis in the presence of water, the company concludes that these esters are more appropriate for hydraulic fluid and grease applications than stern tube lubricants.
Synthetic esters, in contrast, can be designed with optimum chemistries for specific applications. Klubers white paper explains that one type, saturated branched polyolesters, has greater resistance to hydrolysis and are appropriate for stern tube and other marine lube applications. Kluber recommends avoiding emulsifiers, removing free water, maintaining low temperatures and monitoring lubricant condition in order to prolong service lifetime of ester-based stern tube lubes.
RSC Bio Solutions LLC, based in Charlotte, North Carolina, has an alternative approach to formulating EALs for marine applications, using base stocks made from sugarcane.
Bernard C. Roell, vice president of research and development, explained to LubesnGreases that the company had success selling vegetable oil based hydraulic fluids for equipment used in landscaping and golf course maintenance, but these natural esters had limited hydrolytic stability and were less appropriate for marine lube applications. He was also concerned that PAOs, PAGs and some synthetic esters might be regulated out of some lubricant applications in the future, since the European Unions Ecolabel requires a minimum of 45 to 70 percent of a compliant lubricants carbon composition come from renewable sources.
To address these real and potential challenges, RSC Bio began working with Novvi LLC. Novvi is a joint venture started by Emeryville, California-based Amyris Inc. and Brazilian sugar company Cosan S.A.; American Refining Group and Chevron bought into the venture in the second half of last year.
Novvi develops, produces, markets and distributes base stocks and lubricants made from Cosans sugarcane. Syrup from the sugarcane is converted to beta-farnesene, which Novvi calls Biofene, a renewable hydrocarbon molecule. NovaSpec-branded base oils are produced from the beta-farnesene. Products based on NovaSpec have been commercialized to meet VGP 2013 requirements.
RSC Bio used NovaSpec base oils to develop its Futerra-branded lubricants for marine and other applications. Released in early fall last year, Futerra is an Ecolabel certified line of hydrocarbon and related (HEPR) type EALs. Roell noted that while Novvi produces some hydraulic fluids and compressor oils for marine applications, RSC Bio formulates higher viscosity marine lubes for hydraulics and stern tubes, and plans to introduce gear oils and greases in the near future.
Roell claims that they outperform other EALs in several key areas, such as durability, oxidative stability, hydrolytic stability and compatibility with seal materials, including nitrile rubber. Of particular interest for stern tube lubricants and other marine applications, he noted that Futerra lubes demulsify (separate from water) like mineral oil counterparts, reducing the risk of hydrolysis and extending service life.
Thordon Bearings, the Canadian manufacturer of marine and industrial bearings systems, has taken yet another approach to develop VGP-compliant technology for stern tubes. Carter explained that, prior to invention of seals for stern tubes, seawater was used to lubricate extremely dense wood bearings for propeller shafts. Even after lipped seals and petroleum stern tube lubricants were implemented in over 95 percent of commercial vessels, they were not accepted for military and coast guard use. For these critical applications, there was risk of catastrophic loss of lubricant, which would allow propeller shafts to overheat and bearings to seize, leaving a vessel dead in the water.
Thordon worked with navies worldwide to develop bearings and hardware for pumping seawater into stern tubes to lubricate propeller shaft bearings. Carter explained that Thordon equipment pumps seawater through grooves in the upper half of elastomeric polymer journal bearings. When the propeller shaft reaches a critical speed, a hydrodynamic water film is created to support the shaft, similar to an oil-lubricated bearing. Thordon supplies protective coatings for propeller shafts to prevent corrosion from seawater. No aft seal is required to separate oil-based lubricants from the aqueous environment, although a forward seal is used to prevent seawater from entering the engine room.
According to Carter, more than 40 navies worldwide use Thordon seawater-lubricated bearings for propeller shafts, including those of the United States, Canada, Germany, Italy, Australia and Brazil.
Thordon has applied its military experience to commercial vessels because seawater is an EAL that satisfies VGP requirements. Carter noted that over 2,000 commercial vessels currently use seawater-lubricated propeller shafts. These include eight dry cargo ships owned by U.K.-based Carisbrooke Shipping, five of ConocoPhillips oil tankers and 17 Carnival cruise ships (plus two on order). China COSCO Shipping operates 12 bulk carriers and three car carriers with the bearings, and has 20 more systems on order.
Many smaller vessels also use such equipment. The majority of pushboats propelling cargo barges on the Mississippi River and its tributaries use water-lubricated propeller shaft bearings, as do many tugboats, fishing boats and yachts, Carter says.
Continuously pumping clean seawater efficiently removes heat from bearings with no risk of oil leakage. This means the ships also comply with the International Maritime Organizations Polar Code, which came into force in January and prohibits discharge of any oil or oily mixture, including EALs, from vessels operating in polar waters.
While the up-front cost is greater-approximately $300,000 for seawater-lubricated versus $200,000 for oil-lubricated stern tube systems-Thordon points out that the seawater system eliminates operating costs such as mineral oil at 33 cents per gallon or EALs at around $2.77 per gallon, plus oil analysis and used oil disposal costs. Seawater-lubricated systems typically have a 20 to 25-year operating life, and even longer in some ships. The typical lifespan of a commercial ship is 25 years, according to Thordon. Further, the propeller shafts emit low levels of noise and vibration, which can be an advantage for cruise ships.
Will seawater prove to be the ultimate EAL for lubricating stern tubes and other oil-to-water interfaces, or will it remain a niche technology?
Mary Moon, Ph.D., is a chemist with hands-on R&D and management experience in the lubricating oil and grease and specialty chemicals industries. She is skilled in industrial applications of tribology, electrochemistry and spectroscopy. Contact her at mmmoon@ix.netcom.com or (267) 567-7234.