Making maintenance wait

Making an engine last as long as possible calls for careful maintenance. The major overhaul – usually about halfway through an engine’s expected service life – is particularly costly. With some of the mtu Series 4000 marine engines, customers will now be spared this for much longer because the Rolls-Royce Service team has lengthened the times between major overhauls by a significant amount. Indeed, in some cases, a major overhaul will now be avoided completely. This is going to save money, time and resources – as well as cutting carbon emissions.  

Servicing the engine on a ferry or tugboat can quickly become very time-consuming, depending on the situation – during major overhauls, some vessels even have to have their hulls cut open to get the engines out. For the operator, this means high cost and loss of revenue due to what can be up to three weeks of downtime. Rolls-Royce has now addressed this very problem, analyzing vast amounts of data in a two-year project to pinpoint the actual service lives of its mtu commercial shipping engines with even greater precision. The outcome is that the time between overhauls (a.k.a. TBO) is now being significantly extended – and has even doubled in some cases. “We can announce with some pride that this is a major milestone,” said Andreas Müller-Hirlinger from the Commercial Marine sales team.  

In-depth data analysis behind longer TBOs

This milestone is all down to a program of detective work which saw Rolls-Royce's Service Engineering team collate over 50,000 records containing information on the differing load profiles of engines in the field. The team used an elaborate algorithm to sift through this mountain of 'big data'. “Our Service Engineering team led by Jens Schneemann has calculated the wear and tear on engines much more specifically based on individual usage profiles, examining which engine components are worn and in what way,” continued Andreas.   “Using this information, we've been able to make much more accurate predictions about how much longer the engine can ultimately run for, and when what maintenance is due.”    

Until now, the service life of an engine has been determined by how long it can last assuming it is subjected to a full-load usage profile. However, the data has shown that the majority of engines are not at all subjected to a life at the limit. As a result, overall service life has now been extended by a significant margin. “If an engine is not operated at full load, it will naturally last a lot longer,” explained Müller-Hirlinger. Also, the Service Engineering team has pinpointed the engine components that determine the TBO. “The team quickly agreed it was the crankcase and crankshaft. When these are worn out we don't really have any chance of maintaining the engine in the vessel's hull – that's when it has to come out.” Based on the new findings, the team has set the service lives of these two components at up to 90,000 hours. “Before that, there's no need to take the engine out. We can maintain everything else aboard the vessel.”

Less maintenance and longer intervals between overhauls

The team validated its evaluations by buying back old engines with high operating hours. “Colleagues conducted in-depth analyses on the components and measured the wear and tear on them. This has all led to a much sharper picture of what we can trust our engines to do,” said Christiane Kleck, Senior Manager, Marine Service Sales. The next step was for the team to develop a TBO calculation model. This two-stage approach also guarantees the dependability of the new intervals, having been determined via the new computational model and also validated on real-life engines from the field. “That is proof-positive,” concludes Andreas Müller-Hirlinger.
The Rolls-Royce Service Engineering team then adjusted the maintenance schedule for the engines accordingly, re-jigging it to allow as many components as possible to be serviced at the same time, and in so doing achieved yet another cut in TBO. “It was important to us not to jeopardize the reliability of our engines,” said Kleck. “It's still our primary strategy to do preventive maintenance instead of waiting until something breaks.”

What do customers stand to gain from higher TBOs?

For the customer, raising the TBO means, above all, a massive cost saving, because it saves up to one major overhaul during the lifetime of the engine. The elimination of a major overhaul also minimizes the organizational and cost inputs, meaning the vessel operator suffers less – potentially zero – downtime. “In a best-case scenario, an optimized tugboat engine will run for 54,000 hours. A tugboat is considered to have an average service life of 25 years. This means a tugboat is spared a lot of maintenance over its lifetime – that's huge when you consider what it sometimes takes to maintain a tugboat engine,” said Kleck. “In a worst-case scenario, the hull has to be cut open and welded back together again. By optimizing the evaluation of engine data and by improving maintenance schedules and intervals, we're saving the vessel operator serious amounts of money.”

“For us as shipowners, it's important to know the total cost of ownership of our engines in fairly precise terms,” said Lars Peter Mortensen, Technical Manager of Danish tugboat company Svitzer, reflecting a commonly held view. “It looks like the extended TBO is going to cut expected maintenance and associated cost by a significant margin, with some major work not needing to be scheduled during the life of our fleet given our low annual operating hours and engine loads.” He added that when it comes to ordering new vessels and supplying engines, the TBO profile of engine manufacturers certainly has an impact on decision-making. “With a longer anticipated TBO – and accompanying reduction in the total cost of ownership – Rolls Royce Power Systems becomes a more attractive proposition for future orders.”

Another plus is that the longer TBOs mean fewer spare parts and engines have to be produced and transported over long distances, thereby reducing carbon emissions and helping protect the environment.

Extended TBOs to be rolled out to other engines too

Right now, the new TBOs apply to Series 4000 engines for vessels such as ferries, tugboats and yachts. “However, our Service Engineering team will gradually be working its way through other series as well,” said Kleck. Things are already happening in the industrial range, for example for haul trucks and excavators, and colleagues will also be turning their attention to the mtu Series 2000.