Engine Longevity

The ECU absolutely sets the injection events to the best point in the matrix. It is absolutely possible to optimize parameters for the given engine operating point. Fixed pitch or CPP.

Rufus said:

The prop computer and the engine computer would talk to one another and arrive at the best place to take the engine/propeller combination. I don't believe that could be done without actual torque as an input parameter. For one thing torque limits on drive line components would have to be respected.

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This is done in every modern diesel truck. The engine ECU and the powertrain PCU are in real time communication with all parameters. The torque estimate from the ECU is highly accurate for any operating condition. Together they select gear ratio, torque, and rpm. One of the not so well kept secrets is your Cummins in your RAM truck, while rated at 1000 ft lbs, is not allowed to do that very often due to drive train limitations. In fact on the QSB chart note that the torque falls off as you near max rpm, that is an ECU imposed limit to keep cooling and other things in check. The miracle of computer controlled common rail engines is every operating parameter is just a few lines of code.

On a boat you do not have this freedom as prop and transmission are usually fixed. You have an RPM lever and everything else is a dependent function.

Precisely. No question ECUs can set whatever parameters are requested (SKI's comment above). But the current RPM demand control architecture does not and cannot allow for full optimization per the BMEP chart. A variable pitch prop and the appropriate fuel control architecture probably could. I'm still thinking about the use of a torque estimate versus an actual measurement particularly given the "fluid" operating environment for the propeller.

Running Diesels at Ideal Loading for Longevity

Makes sense.

And after observing good fuel and mechanical maintenance practices, Oil is Everything Else.

I'm sorry, but I way disagree with Mr. Zimmerman. He is basically advising that one should have an engine 3 times larger than is necessary. As if one needs a car that must do 210 mph if one wishes to cruise at 70 mph! Preposterous!
If you think about it, a genset often operates near full load for hours at a time and if well maintained, 12 to 15 thousand hours is not an unreasonable figure for a genset's lifespan. Our Onan passed 19,000 hours and was still running well, though maintenance was becoming a problem with things like freeze plugs and other cooling system parts failing.
Diesels love to be run at their rated continuous operating speed with the correct load. Its all about matching the boat's hull shape and weight, the prop, the trans reduction ratio, and engine hp correctly to get the maximum performance and longevity out of any marine engine. The worst thing one can do is just assume that the former owners propped the vessel correctly. Overloading at low RPMs will kill an engine faster than anything other than a complete lack of use and maintenance, and the less one uses any engine, the more maintenance it will require.

foreverunderway said:

I'm sorry, but I way disagree with Mr. Zimmerman. He is basically advising that one should have an engine 3 times larger than is necessary. As if one needs a car that must do 210 mph if one wishes to cruise at 70 mph! Preposterous!
If you think about it, a genset often operates near full load for hours at a time and if well maintained, 12 to 15 thousand hours is not an unreasonable figure for a genset's lifespan. Our Onan passed 19,000 hours and was still running well, though maintenance was becoming a problem with things like freeze plugs and other cooling system parts failing.
Diesels love to be run at their rated continuous operating speed with the correct load. Its all about matching the boat's hull shape and weight, the prop, the trans reduction ratio, and engine hp correctly to get the maximum performance and longevity out of any marine engine. The worst thing one can do is just assume that the former owners propped the vessel correctly. Overloading at low RPMs will kill an engine faster than anything other than a complete lack of use and maintenance, and the less one uses any engine, the more maintenance it will require.

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Delfin said:

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I've been operating diesel engines for more than 5 decades, from single cylinder air cooled portable ones to a few with single piston displacements larger than the cabin many on here sleep in. Never once ran any of them @ 35%. Heck, on many diesel engines, 35% just barely gets the oil and water circulating correctly.

Delfin said:

That million miles average for semi engines translates to around 20,000 hours or around 100 years the way most people use their boats.

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Exactly.
Which is why i'm so amused by the constant fascination with engine life on TF.

It's probably the least costly aspect of boat ownership.
I'm asked often, with all the cruising i do, 5,000 hours in 5 years, if i'm planning on rebuilding my engine?
Ha !
At a 1,000 hours a year, 20,000 hours will arrive when i'm 90 years old.

As long as a boat owner has a modicum of understanding how engines work (excessive heat or cold is bad), the engine is the least of their worries.

"Diesels love to be run at their rated continuous operating speed with the correct load."

"Never once ran any of them @ 35%. Heck, on many diesel engines, 35% just barely gets the oil and water circulating correctly"

Two quotes on the same subject and both may be true, but only for some engines.

Take Yanmar's liberal definition of continuous operation at 200 rpm off of top. If you do that for long with some of their 70-80 hp per liter engines, they will be lucky to last 2,000 hours. But do that with a John Deere or a Cummins continuous duty definition (most Cummins continuous duty engines are rate at 1,800 rpm for genset use) and you will be ok for 5,000+ hours.

Same thing with the second quote. I ran my Yanmar 370 hp engine at 1,600 rpm or about 55 hp or 15% load and it is quite happy there. But most sailboat engines as well as Krogens and Nordhavns run at 50% all day long.

That is why the concept of running at a recommended pct load is pure BS.

A much much better way of looking at it is Tony Athens rule of thumb (supported by various engine builders data sheets) that 35 hp per liter is a good maximum continuous cruising load. And that rule is only good for high performance turbo charged engines. Many NA engines won't make that at full load.

David

Wxx3 said:

Exactly.
Which is why i'm so amused by the constant fascination with engine life on TF.

It's probably the least costly aspect of boat ownership.
I'm asked often, with all the cruising i do, 5,000 hours in 5 years, if i'm planning on rebuilding my engine?
Ha !
At a 1,000 hours a year, 20,000 hours will arrive when i'm 90 years old.

As long as a boat owner has a modicum of understanding how engines work (excessive heat or cold is bad), the engine is the least of their worries.

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I ran a CAT 3208, which is supposed to be a throw away engine due to the lack of wet sleeves, for just over 1,000,000 miles and it was going strong when I sold the truck it was in. In cruising terms, that's around 20,000 hours. The 3306 I have in Delfin is reputed to be a 50,000 hour engine if you follow CAT's maintenance and load advice, which is > than 30% load. I'll sell her to your great grandchildren and they'll still be able to cruise her for a couple of decades.

IMHO, the 35% load recommended by an expert like Zimmerman seems about right, as long as you spend some time every day or so heating the engine up to minimize slobber and carbon buildup.

I've installed bypass filters and use synthetic oil not because I think that if I didn't my engine would fail, but for the same reason I clean the attic now and again. Pride of ownership, which to me translates to trying to take good care of my toys.

And speaking of CAT:

"If maintained properly, diesel and gas generator sets can operate at light loads for long periods of time with no harmful effects. After operation at low load levels, each impacted generator set should operate under increased load to raise the cylinder temperature and pressure, which cleans the deposits from the combustion chamber."

- http://s7d2.scene7.com/is/content/Caterpillar/C10711038

BandB said:

(snipped...)

Where it becomes really interesting is looking at jet RIB's, both gas and diesel. I might have to do that later, but back to a meeting for now.

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I'm curious. Has your meeting finished yet?

foreverunderway said:

Diesels love to be run at their rated continuous operating speed with the correct load. Its all about matching the boat's hull shape and weight, the prop, the trans reduction ratio, and engine hp correctly to get the maximum performance and longevity out of any marine engine. The worst thing one can do is just assume that the former owners propped the vessel correctly. Overloading at low RPMs will kill an engine faster than anything

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I think I'm a victim of this. My old boat's previous-previous owner took her from CA to Hawaii then on to Aussieland and back. The 1600 gal tank wasn't big enough so he filled the cockpit with fuel drums. Be he also slightly over-propped it with Kort nozzle props, to maximize his efficiency at planned operational speed.

It was a very strange setup, but the old log book was more fascinating to read than anything Melville or Verne. It definitely beat up those Jimmies, but they still ran strong.

I did switch out the props but kept the old ones as spares.

Insequent said:

I'm curious. Has your meeting finished yet?

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Yes, and we've made it home. I haven't looked at those numbers though. Just been glad to be home.

Normally cruise at 6.3 knots at 1800 RPM, representing a 43% load. RPM of 1600 results in 6.0 knots for a 38% load. Regardless, expect the JD 4045 to outlast me.

I am glad to see that my article stimulated some conversation on this subject.

I would like to clarify a couple of points. First, the determination about how hard an engine should be pushed must be based on the rating of your particular engine. Cummins, for example, offers Continuous Duty and High Output ratings (along with others in between). Continuous Duty means they designed it to run at full power nearly all the time (commercial push boats for example).

The High Output rating is what almost all recreational boats have. Cummins specifies a power factor of 10-30% for these engines. Those who have a recreational rated engine and who push that engine at power factors of, say, 50-70% will experience shorter time between overhauls.

Second, I emphasized in the article that it is equally important for those who do run at light loads, to periodically run their engines up to WOT or to 80% load. The article included more detail about that protocol.


I hope these comments are helpful.

Steve Zimmerman

the prop curve is a mathematical estimate of propeller load.

The equation is simple ((running RPM/max Rated RPM)^2.7)100= percent load

The 2.7 exponent is common though exponents from 2.5 to 3 are reported.

((2400/2600)^2.7)*100=80.5 %

Substitute your own numbers and paste it into your search box

SteveZ said:

I am glad to see that my article stimulated some conversation on this subject.

I would like to clarify a couple of points. First, the determination about how hard an engine should be pushed must be based on the rating of your particular engine. Cummins, for example, offers Continuous Duty and High Output ratings (along with others in between). Continuous Duty means they designed it to run at full power nearly all the time (commercial push boats for example).

The High Output rating is what almost all recreational boats have. Cummins specifies a power factor of 10-30% for these engines. Those who have a recreational rated engine and who push that engine at power factors of, say, 50-70% will experience shorter time between overhauls.

Second, I emphasized in the article that it is equally important for those who do run at light loads, to periodically run their engines up to WOT or to 80% load. The article included more detail about that protocol.


I hope these comments are helpful.

Steve Zimmerman

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Thanks Steve both for the article and your comments.

One question I have regarding rating. When I purchased Delfin, she had a new CAT 3306 C rated engine. The previous owner was a Naval Architect whose hobby was buying classic boats and refitting them. More money than brains, apparently, but in any case, his reasoning for using a C rated engine was that since it would be operated at around 25 - 40% load factor, the C rating was fine. I do take it up to EGTs of around 775 degrees every few hours to heat everything up. The C rating has the following parameters: load factor <70%, annual hours <3,000, max power per day < 1 hour.

My question is, how many actual physical differences are there between engines of the same manufacture and model, but different ratings, or are they primarily how the engine is governed? If the latter, then isn't rating somewhat unimportant in a full displacement vessel since whatever the rating, the engine will likely be run at less than 40% load?

Jay on Westerly published a fuel consumption table that pretty much reflects what I see on a Cummins 6CTA 8.3 CPL1929. Using the approach of WOT fuel consumption versus measured fuel consumption over time, I come up with engine loading averaging around 9%. With 360 hours my average fuel consumption was 2.1 GPH (Fuel used divided by engine hours). I can achieve the WOT RPM with my current prop of 2650 RPM with a specific fuel consumption of 23.3 GPH at 2600 RPM on the Cummins Performance Curve. I would call that lightly loaded over time and tracks with our typical running RPM of 1250-1400 (7-8 knots).

Tom

Delfin said:

, but in any case, his reasoning for using a C rated engine was that since it would be operated at around 25 - 40% load factor, the C rating was fine. I do take it up to EGTs of around 775 degrees every few hours to heat everything up. The C rating has the following parameters: load factor <70%, annual hours <3,000, max power per day < 1 hour.

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Surely that one hour per day, sucking like the proverbial, negates any fuel savings gained over the several hours previously by running slow?

Simi 60 said:

Surely that one hour per day, sucking like the proverbial, negates any fuel savings gained over the several hours previously by running slow?

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Good point Simi. Some smart engine guys say that provided your oil temps are 180 to 190F that the one hour "high" load run up per day is an anecdotal reference to the 2 stroke DD era.

Dry stack complicates the issue too with lower exhaust gas temps causing stack coking, thus another reason for some to run periodically at "high" loads.

With all these rules of thumbs I need more hands. Or as many on this thread have said, run sensibly for your specific application.

Gordon J said:

You are my new hero. That you keep the vehicles so long is amazing in this current throw-away society.

Gordon

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I own a 2003 Chevy Duramax with 290,000 miles that runs the same as when new. By-pass filtration since new. No rust to boot.

"Overloading at low RPMs will kill an engine faster than anything"

While this is true , simply increasing the load at lower RPM can increase engine life , reduce fuel burn and make lofe onboard better with less noise and vibration.

The key is a PROPER load for the chosen RPM ,NOT an overload.

With a higher load at cruise , there should never be a need to run at WOT to "clean out the engine" .

An EGT gauge is a great idea , just to be sure, of no overloading.

makobuilders said:

There have been a few comments here about the key to long engine life being keeping the oil clean with aftermarket bypass filters, Gulf Coasts, centrifugal polishers, etc.

However I've always thought that just running the engine properly, monitoring EGT and sticking to the manufacturer's recommended oil change intervals should be good enough, without having to resort to expensive aftermarket items or synthetic oils.

Is there really some magic to these aftermarket items?

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Synthetic oils allow for extended drain intervals so, no, they are not more expensive. Plus, they minimize, comparatively, the start-up wear. By-pass filtration is quite effective at removing soot particles down to 1 micron as opposed to standard filters at 30 microns. Not magic, just science.

sunchaser said:

Good point BK. Interestingly, Steve Z's PM article states 80% load is around 90% rated RPM. He must have been peeking at a JD sheet. On most marine engines, 35% load is 60 - 70% rated RPM.

Regarding pre-failure analysis (or better said repair it before it breaks) it is commonly done for tens of thousands of variable use engines under extended warranty programs. Especially during the last few decades as on engine diagnostics are downloaded during routine maintenance and oil sampling.

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Getting back to Ford Lehmans, a 35% load (65% of rated RPM of 2,500 RPM) yields about 1,650 RPM. I think most Lehman owners run their engines between 1,600 and 1,750 RPM, perhaps 1,800 on occasion when necessary.

Simi 60 said:

Surely that one hour per day, sucking like the proverbial, negates any fuel savings gained over the several hours previously by running slow?

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The 1 hr Max at WOT is the Cat spec for the C rated engine. My specific use pattern is 20-30 minutes with the EGT >= 750 degrees every 24 hours, or daily if we're making shorter day trips. GPH goes from 3.3 at 7.5 knots to 8 GPH at 8.9 knots, so yes, total fuel economy goes down but not enough to worry about. There is no point in my ever going to WOT at 2200 rpm since I hit hull speed at around 1850 rpm and any additional power provides no additional speed and only a slight increase in EGT.

catalinajack said:

Synthetic oils allow for extended drain intervals so, no, they are not more expensive.

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While that is what the oil manufacturer claims, the engine manufacturer's warrantee department may disagree. According to the manuals for the diesels I own (Ford, Yanmar, Cummins, Volvo) there is no allowance in maintenance interval for synthetics.

Delfin wrote;
“My question is, how many actual physical differences are there between engines of the same manufacture and model, but different ratings, or are they primarily how the engine is governed? If the latter, then isn't rating somewhat unimportant in a full displacement vessel since whatever the rating, the engine will likely be run at less than 40% load?”

I see the perfectly powered (loaded) engine in a FD rec trawler as about 60 or so percent. Mine is 50% and I know I could do easily w less power. But it depends on who or what rates the engine. My Mitsubishi is a generic industrial engine. And Westerbeke and Vetus both claim more power .. 44 and 42hp.

Nomad Willy said:

Delfin wrote;
“My question is, how many actual physical differences are there between engines of the same manufacture and model, but different ratings, or are they primarily how the engine is governed? If the latter, then isn't rating somewhat unimportant in a full displacement vessel since whatever the rating, the engine will likely be run at less than 40% load?”

I see the perfectly powered (loaded) engine in a FD rec trawler as about 60 or so percent. Mine is 50% and I know I could do easily w less power. But it depends on who or what rates the engine. My Mitsubishi is a generic industrial engine. And Westerbeke and Vetus both claim more power .. 44 and 42hp.

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My question related more to what the mechanical differences are between engines of different ratings. Is it only the governed rpms, or are their others?

Delfin,
I don’t know.
But exhaust valves may be of a better alloy. Pistons also. Lots of things could be different to handle higher loads and temps for longer periods of time.
Old Dodge flat head truck engines had different exhaust valves and there may have been many more differences. GMC made more than one 6 cyl engine for trucks. The V6 found in the GMC trucks (not found in cars) in the 60’s was designed specifically for trucks. Quite sizeable trucks at that. I remember I was amazed at thecooling system. Was a great engine but not very fuel efficient. Otherwise it would have been a good boat engine.