[Codger]

I'm trying to get a handle on the service life of some of the larger power plants.
I can't seem to find any specifics on MTBF or fixed overhaul schedules. Granted, many of the large yachts seem to spend more time at the dock than out on the sea, but is there any information on actual usage hours. I looked at MTU and they go on about 24,000 being in service. An engine that sits for 350 days a years might be in service but so what. If Skat was to spend 180 days a year actually out at sea at cruise speed how long would the powerplants run before having to be overhauled?

[Garry Hartshorn]

Every engine manifacture has a different specification which may change between diffent models but for instance MTU from memory which is a couple of years now does the following

W1 Daily checks, oil level, coolant level, general visual check
W2 250 - 500 hours depending on model and if bypass filters are fitted
an Oil & Filter change
W3 1000 hours adjust valves check injectors
W4 2500 hours water pumps and other ancillary equipment serviced
W5 5000 hours essentualy strip top end
W6 10 000 hours total rebuild

each level also includeds the previous levels of maintenance.

[Codger]

Thanks. That gives me something to work with.
Annualising downtime numbers over a ten year period based on what my usage would be.

Are most of the large yachts actually designed so that pulling a powerplant for overhaul is straightforward?

[YachtForums]

It’s difficult at best to project general answers, as there are so many variables involved. Certainly, engines have a design life. They are generally intended to provide a minimum number of hours for a given application, but this ranges from heavy duty, to continuous service, to light duty. Each manufacturer has different models, with varying design lives, or MTBF (mean time between failure).

We have often thrown numbers around like 1500 hours for traditional gas engines and 5000 hours for diesel engines… between overhauls. These are by no means “real” numbers, they’re just a general rule of thumb we’ve adapted over the years. Your mileage may vary. You could easily double those numbers… if you’re willing to go slow... I’m not.

Keeping a proper maintenance schedule, coupled with staying within the operational parameters the motor was designed for should certainly increase engine life, but there are so many other culprits, it is again… impossible to speculate. Operating conditions and maintenance are the real variable here. No engine will survive without proper maintenance. Overheating just once could ruin an engine, whether it has 20 hours, or 20,000 hours. Failure to maintain the cooling system is probably a more common reason for failure than forgetting to change oil and filters. Another culprit is carbon build-up on the heads and pistons, which is a typical reason for needing an overhaul.

Engine R.P.M. is certainly a consideration. Generally, the higher the RPM’s, the shorter the engine's life will be. Or, the heavier the resistence (load) the more stress is generated. Both will reduce engine life. But pushing the throttle further doesn’t necessarily mean “go-faster”. Displacement boats for example, are a very different scenario. If you have a pure displacement hull, no matter how much more power you throw at it, you won’t go much faster. Any extra horsepower, beyond the speed limitations of the hull is simply wasted.

Within the standard selection of marine diesels, most manufacturers have different ratings for basically the same engine block. For example, let’s take a small, normally aspirated motor rated at 250 horsepower. You can expect to get a full 250 horsepower for long hours. The same basic block with a turbocharger may be rated 350 horsepower. Add an intercooler and some mods, and you’re pushing 400 horsepower. The're all the SAME block, so.. in my futile mind, it’s pretty simple math… the harder you push it, the shorter its life will be. No matter what engine you choose, or comes with the yacht… the life of the engine is directly proportional to the amount the throttle applied. Ask me how I know!!!

Bare in mind, today’s engines are built to much finer tolerances than ever before, hence break in periods have shortened substantially over the years. They will also accept much more abuse and therefore, we can generally expect a much longer life than ever before.

I'm looking for some wood to knock on after that last sentence!

[Codger]

Thanks. I've cacked my share of engines in my life. Playing with methyl ethyl keytone mixes in a Merc 110 BP was dramatic.
Blew a bottle fed Suzuki GSXR last year. Putting a piston through the head of a Lycoming IO360 was very loud and the relative silence afterwards was deafening, makes it easy to concentrate on looking for a place to glide to.
I've also put 300k miles on a benz 300sdl by taking care of it.

This just started as a Hmmmm... what if sort of thing. Calculated that the minimum travel that I'd do in a yacht worked out to 3331 hours at 20 knots in a year. I just used 20 knots as an off the wall number. My life would be much simpler if I'd never come across a photo of Skat. Never would have really contemplated actually travelling on a yacht for anything over a week cruise here and there. I didn't have any idea that the communications systems were available for a yacht until I started looking around this site. Realisation came to me that one could actually live aboard for extended periods and still keep on top of business. Probably sounds silly but that was a real revelation for me.
That 3331 number is what got me looking at maintenance and downtime.

[Garry Hartshorn]

Well put. I agree totally in the most part but assuming that the engine is not flogged to death the modern engines are great and getting better. Compact, light, short stroke, turbo charged, intercooled, high RPM engines inherantly need more maintenance than the older bulky, heavy, long stroke, naturally asperated engines. What really puzzles me is that it is obvious that to go fast you need lots of power and minimum weight so you would not use and older style engine in a 30+ knot yacht but when you are talking about a 12 knot heavy displacement yacht why would you use a high performance engine ????? a bit like putting a Fararri engine in a Mack truck.

As far as to the question about pulling engines for maintenance it is generaly done with the engine in position and most engine rooms are well enough thought out to do this. But I have been unfortunate enough to have worked on yachts where this would be nearly impossible so for all potential yacht owners my advise is take the crew who you will be employing and who's loyalty should be towards you and ask their opinion and weigh that against the opinion of the individual who is working for commision or a short term contract. I did read about a 6'5" engineer it would be unwise in my opinion to put him in a engineroom with the majority of the space had only 5' headroom.

[YachtForums]

Skat... really? Now THAT's a different story. Expect to rebuild atleast every 50 hours... 'cause the US Navy's gonna constantly mistake you for a hostile.

I'd prefer the Millennium 140 when being chased by torpedos.

[Codger]

Back to Skat. Skat can't cruise at 20 knots so the 3331 hours doesn't compute. I'm sure that if i called AMG and asked him to reinvent Skat so that it would cruise at 20 knots it could be done

720-hp 16V4000 M79 MTU are the powerplants. Assuming that regular maitenance can be done just about anywhere. How much downtime would be involved in an overhaul?

[Codger]

Originally Posted by YachtForums

Skat... really? Now THAT's a different story. Expect to rebuild atleast every 50 hours... 'cause the US Navy's gonna constantly mistake you for a hostile.

I'd prefer the Millennium 140 when being chased by torpedos.

Only port of call in the US would be Boston once a year.

[YachtForums]

Certainly Lars can design a new Skat. A hull capable of cruising at 20-knots is very do-able. I happen to know someone who can help.

As for re-builds... the actual labor time is not all that long if you have a proficient mechanic. It could range from a few days to a couple of weeks. On the Millennium 140, a Pax-18 was pulled out and replaced in 2 days, in order to make it to the Ft. Lauderdale Boat Show last year. By the way... that motor didn't come out in one piece, nor did the new one go back in as one piece. Moral... throw enough money at something and you can create a time warp.

The real time will be consumed in sourcing the parts and machining the existing components. Add a multitude of other things that can go wrong in the dis-assembly and/or re-assembly... and the hours turn into days. It's not really the time these projects take... the real cost is in the time they take away from your business. That being said, hiring a good mechanic and chief engineer... is money well spent.

[Garry Hartshorn]

3331 hrs a year

W1 15 minutes per engine
W2 3 hours per engine
W3 1 day per engine if no major faults or problems
W4 2 days per engine if no major faults or problems
W5 10 days per engine if no major faults or problems
W6 Never done one

Most yacht engineers are capable of up to W4 though many prefer to have a tech on site for a W4 which in my opinion is a good insurance policy. But as there are many complex systems on a large yacht you should expect the engineering downtime to be around 1 month per year, but this may vary quite a lot depending on age, quality and accessability of equipment.

[Codger]

"Moral... throw enough money at something and you can create a time warp. "

I think I used the old line, dating myself, put enough power to it and you can make a brick fly.

I'm really trying to stay away from the calculating the dollar side of it. More, just the phyical feasibility of a yacht. I've been through rebuilds of other large diesels and the completion target moves from day to day.

[Codger]

Thanks Garry
A month a year in downtime is the number that I was looking for.

[brianwill]

From the original thread question, Carl had it right on. Proper maintenance and keeping the rpms at maximum continuous (or less) will significantly extend engine life. Put the hammer down and you lose longevity at an exponential rate. Some of the newer high rpm diesels are needing overhauls at 1000-1500 hours--just like a gas engine but a whole lot more expensive to buy and overhaul.

[Mark in SBA]

In addition to revs, doesn't proper loading also result in increased MTBO? With the much larger diesels, such as Cat's 35 and 36 series, I've seen a quite a few controllable pitch propellers or diesel/electric drives used as a means to optimize loading. Also, wouldn't engine electronics also tend to increase overhaul intervals vice traditional mechanical governors and injector pumps?