On May 15, the distress call came from the crew of a 200-ton trawler, broken down and disabled in the Atlantic Ocean some 24 miles from Lands End in Cornwall. Reached and secured by the lifeboat City of London III, the trawler was towed back to harbor long after dark, an exhausting 10 hours later.

The mayday on April 30 arose from two fishermen aboard a lobster boat in trouble off the Wexford coast of Ireland. This time it was the swift response from the lifeboat crews of Kilmore Quay that delivered the distressed men and their boat from peril.

The common factor in these sea stories is the Royal National Lifeboat Institution, also known simply as Lifeboats, which operates 237 life-saving stations along the coasts of the United Kingdom and the Republic of Ireland. This nearly 200-year-old charity maintains more than 350 lifeboats dedicated to saving lives at sea. No matter the time of day or weather, it aims to launch on average within 10 minutes of getting a call for help, a benchmark it proudly met in 2012. Last year alone, Lifeboats launched 8,346 times and rescued 7,964 people – 22 a day.

It costs 140.5 million (U.S. $213.4 million) a year to run the RNLI, which besides maintaining the stations and lifeboats also trains lifeguards to patrol U.K. beaches in the summer and conducts safety awareness campaigns. All costs are covered by private donations and legacies, with zero central government funding. With one all-weather lifeboat costing upwards of 2.7 million and one-third of its operating budget spent on maintenance, extending equipment life has become a big concern. So in recent years Lifeboats has embraced condition based maintenance to reduce unplanned repairs and maintenance on vessels. The payoff has been huge, an estimated 6.6 million saved in 2011 alone.

All-weather lifeboats, which have a range of 250 nautical miles, make up more than a third of RNLIs fleet and include four classes of ships: Severn, Tamar, Tyne and Trent. But unlike other workboats like ferries, tugs or fishing boats, lifeboats see relatively infrequent use, points out Mayank Anand of Bournemouth University in Dorset. They may be called out for an ocean rescue operation once a day during the summer season, or sit unused for weeks on end in remote locales. Although they regularly go out for routine sea trials, lifeboat service epitomizes the extreme stop-start conditions that exact the worst toll on engine life.

Outside of rescue operations, the boats may be used for only one or two hours a week, and remain on standby for long periods. This means the engine oil is not being circulated, and it drains from the engine and stays in the sump, Anand explains. But when action comes, there can be no holding back, he adds. If theres a call for help, the lifeboats must go from a sudden start right to maximum power, and are subjected to high-speed cruising and high loads.

Recognizing that engine readiness is critical to its mission, RNLI turned to Anand, a research graduate, and Prof. Mark Hadfield at Bournemouths school of Design, Engineering and Computing, for help in its oil condition monitoring efforts. Funded in part by BP Technology, they are investigating how well the ships oils are performing, and if theres a clear point at which their useful life begins to deteriorate and engine wear accelerates.

In mid-May, Anand traveled to Detroit to present his initial findings at the annual meeting of the Society of Tribologists and Lubrication Engineers. He began by describing the all-weather lifeboats, each of which carries a crew of six or seven and is equipped with a pair of marine diesel engines capable of speeds to 25 knots. The all-weather lifeboats are scattered across hundreds of locations, many of them quite lonely, he remarked, and with a wide range of temperatures and conditions.

The oldest in the fleet are the Tynes, which are nearing the end of their expected 25-year life. Tynes have twin GM 6V92 marine diesel engines with 425 horsepower each. Next-oldest are the Trent class lifeboats, last built in 2003 and equipped with twin MAN D2840 LE marine diesels capable of 850 hp. Severns have twin Caterpillar 2412 diesels, 1,250 hp each. And the newest in the fleet are the Tamars, which were introduced in 2005, have 1,001 hp Caterpillar C18 diesels, and are gradually replacing the Tynes.

All of the ships use commercially available SAE 15W-50 marine diesel engine oil, and one of Anands first tasks was to review several years of oil condition reports. I was given reports with standard oil sampling and tests, such as ICP, FTIR and kinematic viscosity, he related. There had been 4,000 tests performed from 2009 to 2012 by the RNLI, and my goal was to see if the results could be used to improve the serviceable life of the equipment.

Lifeboats bases its oil change intervals on hours of operation, in accordance with OEM recommendations, but these hours can stretch out over many seasons for some engines, he continued. With the average life of the oil being about 300 hours, some boats may go two or three years without an oil change, except some that may be added every two or three months during inspections.

Reviewing the thousands of reports, Anand began to see some trends. Outside of the hour-based intervals, he observed, engine oils also were changed when a red flag was spotted during routine oil analysis. Narrowing his focus to the MAN engines on the Trent lifeboats, he noted that one key reason for an oil change was ferrous debris, although the lab analyses also spotted fuel dilution and coolant leaks.

Fuel dilution and coolant leaks suggest seal issues and may be easy to fix, but ferrous debris can be a harbinger of engine wear. Of 670 reports dealing with the MAN 2840 diesels, 82 percent had iron above the 22 ppm level, and the iron concentration usually increased with time, pointing to worsening damage. The ferrous levels ranged from 4 to 158 ppm, but averaged 47 ppm, Anand said.

What was the source of this ferrous debris? That part of the puzzle was simple, he said in Detroit. Each MAN D2840 has 10 cylinders and liners, and the liner material is grey cast iron. So obviously that was our main source of ferrous particles. His next steps were to review the wear debris reports on the used oil from the 300-hour point on the Trent engines, to see if they held more clues, and to work with samples of the diesel oil itself.

We decided to analyze the antiwear performance of the oil at regular intervals from zero to 300 hours to see when the wear was starting to happen, Anand said. For this work, he used a device called a high-frequency reciprocating rig, a tribotester that measures pure sliding and reciprocal motion. The 10 hour test at 100 degrees C. would simulate the contact forces between the piston ring and the cylinder liner.

The experiment used two sets of samples, one being fresh 15W-40 engine oil and the other being aged oil taken after 300 hours of service in Trent lifeboats. Each test was run three times, and then the wear scars from the tribotester were compared at microscopic levels. Oil life certainly seemed to make a difference, as the wear scar was about three times larger with the used oil than with fresh.

The next rounds of testing will involve more samples, taken at regularly spaced intervals throughout the 300 hours of service. Ongoing experiments will help us get to the real-time condition of the oil, Anand reported. What we want is a critical limit, a safer limit for when the lube can be used – and when it should be discarded. He hopes to see the research widen to include the Caterpillar engines on the Severn and Tamar ships, as well.

Eventually, the plan is that actual oil condition will determine how often each lifeboats oil is changed, not merely hours of service. This could be useful knowledge also for operators of ferries and other hardworking boats, Anand commented, because they also leave port, zoom up to maximum load, and then shut off their engines when they reach their destination, before starting up again a few hours later.

RNLI aims to minimize the wear and tear of such severe service by keeping its engine oils in the peak of health.