Babying a diesel engine

[Squanderbucks]

Most Diesel engines come in various setups for the same engine block at different hp ratings. These ratings give specifications about what power output should be done. Example. Full throttle not more than 2 hours out of 8 running. Or not above a certain rpm for mor than 8 hours out of 24. ETC.
but basically if you prop the boat right do it is able to achieve at least 100 rpm OVER the rated WOT setting then you should be able to run the engine at any speed you want up to around 80% or do indefinitely. WOT occasionally if needed for short bursts. But definitely Not lugging along at 1100-1200 for long periods. Also best way to kill a diesel is to Over Prop it not allowing it to achieve top rated RPM.

[Hoodsail]

This season will be shooting for 7knots with my westerbeke w30!! Definitely going to “run it like I stole it”!!

[Cadence]

Originally Posted by Fore and Aft

As a marine surveyor I go on a lot of sea trials and I often hear owners say they do not push their Diesel engine beyond a certain rpm. I used to be in the same mindset thinking that the lower rpm will help the engine live longer?
But for years I have been observing trucks, earth moving equipment and even my Kia diesel car (320,000km). These engines all still last a long time despite being flogged fairly hard. So is it really going to make a difference to my engine life if I run my Yanmar 2GMF at 2000 or 3000 rpm?
Cheers

JMHO! Running at 3/4 rated will probably help on wear eg. bearings. Not wrapping it up periodically is going to establish a cylinder ridge which will play hell with the rings when it is wrapped up.

[SteveSadler]

Unlike a car engine, marine diesels are low HP for their displacement, so running at full throttle won't cause excess wear. The most common problem is carbon buildup. To prevent that the exhaust temp must be hot enough to completely burn all the fuel.
Most sailboats run at low loads for best fuel consumption, but running at full throttle for 20 minutes will prevent carbon buildup according do Volvos manual. I had white smoke at higher rpms when I bought my boat, so I pulled the injectors and found large gooey chunks of carbon blocking the nozzles.

[Cpt Mark]

Originally Posted by slug

diesel engines are rated by duty cycle ...load rating

Continuous duty industrial engines..load rating 100... can run continuously at 100 , full load, and achieve the designed service life

Typically a pleasure boat diesel is load rated at 30

I've never seen a load rating on any diesel engine. Where did you get this from?

[Cpt Mark]

Small boat diesels are designed to run at certain rpms. You have a max rpm and if you're propped correctly you should be able to achieve that rpm and run like that all day long.

What you will also do by running at max rpm is burn a lot of fuel for not a lot of extra speed so often times someone might say the sweet spot is XX rpms and by that they mean that at this rpm I get the best marriage of GPH and MPH.

[Cadence]

Originally Posted by Cpt Mark

Small boat diesels are designed to run at certain rpms. You have a max rpm and if you're propped correctly you should be able to achieve that rpm and run like that all day long.

What you will also do by running at max rpm is burn a lot of fuel for not a lot of extra speed so often times someone might say the sweet spot is XX rpms and by that they mean that at this rpm I get the best marriage of GPH and MPH.

I'd agree. And the sweet spot (as you call it) isn't brain surgery you can hear it.

[slug]

Originally Posted by aquafacts

I have been a diesel mechanic my whole life - (45 years experience and counting) I have worked on big ones (500 hp), little ones and everything in between-stationary, off road/ agricultural/over-the-road trucks and most recently (25+ years)numerous brands of marine DIESEL engines. I maintain and repair diesels and do many re-powers each year - mostly in sailboat service. NEWS FLASH - We KILL them with KINDNESS ! Think about how a diesel engine operates in generator service - starts up cold - governor take it right up to it designed RPM -(very close to designed MAX rpm and out of your control) before oil press. barely gets up and no load -they scream wide open and last 20,000 hours + before re-con (not replacement). I teach Diesel maintenance courses and tell people - don't baby them - "drive it like you stole it " Clean air, clean fuel, clean oil - run as close to max operating temp (but not overheat) and they will last indefinitely.

Remember a marine diesel has many bolt on rotational components pto..alternators, sea water pumps, couplings

All of them have a rotational life

Also consider heat build up in confined..many times poorly designed engine rooms ...high output..high heat

I prefer to “ baby “ a diesel

75 percent cruise ..with occasional 100 percent power blasts

[dadster3]

The answer is in your engine owner/operating manual. I can't believe it would not be there, but if not, the service manual will have it. My impression is that the OP is getting a lot of opinion which may or may not be right. Read your manual.

[bongo]

As a marine engineer with extensive diesel experience I can offer a few rules-of-thumb. Main Engines on container ships can be 40,000HP+, but a diesel is a diesel.
1)We commonly operate the “motor” at 80% of design load. Idling for long periods is bad.
2)If an engine gets “de-rated” it commonly needs to have different turbos and other accessories replaced too.
3)We baby them on the way up to operating temp/rpm, and we baby them on the way down from sea speed. The power is increased or decreased according to a load program curve.
4)On my own boat, with a Westerbeke 40, I pitched the prop so that I could not quite get to the maximum RPM. She runs at hull speed at ~2200RPM. Pushing it harder just burns more fuel. The temp and the oil pressure are good, and the vibration/noise is minimum. I like the engine to be loaded up at a somewhat lower RPM, (no turbos to consider). So, I agree with many of the people above. And make sure you use a lube oil meant for Diesels and not gasoline engines, and change it regularly. And, as mentioned above, listen to your engine.

[slug]

Originally Posted by Cpt Mark

I've never seen a load rating on any diesel engine. Where did you get this from?

https://www.volspec.co.uk/pdfs/Rating-Definitions.pdf

https://www.cummins.com/engines/marine-ratings

https://dicksimonyachts.com/blog/boa...em-definitions

Slight difference in terminology between manufactures

[rbk]

Originally Posted by bongo

As a marine engineer with extensive diesel experience I can offer a few rules-of-thumb. Main Engines on container ships can be 40,000HP+, but a diesel is a diesel.
1)We commonly operate the “motor” at 80% of design load. Idling for long periods is bad.
2)If an engine gets “de-rated” it commonly needs to have different turbos and other accessories replaced too.
3)We baby them on the way up to operating temp/rpm, and we baby them on the way down from sea speed. The power is increased or decreased according to a load program curve.
4)On my own boat, with a Westerbeke 40, I pitched the prop so that I could not quite get to the maximum RPM. She runs at hull speed at ~2200RPM. Pushing it harder just burns more fuel. The temp and the oil pressure are good, and the vibration/noise is minimum. I like the engine to be loaded up at a somewhat lower RPM, (no turbos to consider). So, I agree with many of the people above. And make sure you use a lube oil meant for Diesels and not gasoline engines, and change it regularly. And, as mentioned above, listen to your engine.

That’s another good point about babying up and down. See plenty of people both gas and diesel get out of the harbour and put the rpm from just above idle to cruising rpm say 800-2200 (4-5k on gas jobs) and let the boat speed catch up and the same coming down; come screaming in until right at the harbour then drop from full speed to near idle. I’ll increase/decrease the rpm on the way up in 2-3 increments until it’s at cruising rpm same coming back. I’m also in the habit of taking a look at the engine running on cool down to see if anything stands out before shutting it down. Then check all fluids before closing up, even if we’re running again in the morning. Then i recheck fluids before starting.

[kenbo]

Originally Posted by bongo

As a marine engineer with extensive diesel experience I can offer a few rules-of-thumb. Main Engines on container ships can be 40,000HP+, but a diesel is a diesel.
1)We commonly operate the “motor” at 80% of design load. Idling for long periods is bad.
2)If an engine gets “de-rated” it commonly needs to have different turbos and other accessories replaced too.
3)We baby them on the way up to operating temp/rpm, and we baby them on the way down from sea speed. The power is increased or decreased according to a load program curve.
4)On my own boat, with a Westerbeke 40, I pitched the prop so that I could not quite get to the maximum RPM. She runs at hull speed at ~2200RPM. Pushing it harder just burns more fuel. The temp and the oil pressure are good, and the vibration/noise is minimum. I like the engine to be loaded up at a somewhat lower RPM, (no turbos to consider). So, I agree with many of the people above. And make sure you use a lube oil meant for Diesels and not gasoline engines, and change it regularly. And, as mentioned above, listen to your engine.

I'm not sure how you're defining hull speed but to many it's 1.34 x square root of the LWL. On your boat that's 7.8 kts., so with 26,000 lbs. displacement that's 51 hp at the prop. I'm fairly certain that your 37hp W40 isn't doing hull speed at 2,200 rpm. At 2,200 your W40 is producing about 14 hp at the prop. Which I estimate to be around 5.2 kts.

[Cadence]

Originally Posted by bongo

As a marine engineer with extensive diesel experience I can offer a few rules-of-thumb. Main Engines on container ships can be 40,000HP+, but a diesel is a diesel.
1)We commonly operate the “motor” at 80% of design load. Idling for long periods is bad.
2)If an engine gets “de-rated” it commonly needs to have different turbos and other accessories replaced too.
3)We baby them on the way up to operating temp/rpm, and we baby them on the way down from sea speed. The power is increased or decreased according to a load program curve.
4)On my own boat, with a Westerbeke 40, I pitched the prop so that I could not quite get to the maximum RPM. She runs at hull speed at ~2200RPM. Pushing it harder just burns more fuel. The temp and the oil pressure are good, and the vibration/noise is minimum. I like the engine to be loaded up at a somewhat lower RPM, (no turbos to consider). So, I agree with many of the people above. And make sure you use a lube oil meant for Diesels and not gasoline engines, and change it regularly. And, as mentioned above, listen to your engine.

JMHO, I think you are over propped loading the engine.

[a64pilot]

There are many misconceptions, for one it’s more common than you think for a major engine manufacturer of large Agricultural / Commercial engines to ensure that wide open, isn’t really wide open. Derating a motor leads to a long life and that leads to a good reputation.
They are very often derated and this is done to ensure long life, remove or defeat the governor and they are capable of much more power.
To see motors that are often run hard, look at the big Sportfishing crowd, I mean the big boats that are often run at 200 “off the top” or so, and ask how long they go between overhauls.
Ask the guys with the big turbo DD’s how long they last, where a NA DD if not run too hard will last nearly forever, literally.
I used to run into this line of reasoning all the time with customers and turbine engines, they would say it’s rated for continuous operation at 101% NG and xxxx C temp, why shouldn’t I run it at those numbers, well the reason is it will shorten the engines life is why, sure do it, but your going to pay a lot more at TBO time.

The argument of generators running wide open all the time is a little incorrect, they usually run either 1500 or 1800 RPM, and that’s not often wide open on a motor that is in other uses rated for much higher RPM, their really isn’t small special generator motors, they are simply off the shelf little motors selected for their output power at 1500 or 1800 RPM, and yes look at how long they last, they often last a very long time.
Now great big huge power station generators may well have special motors, but not smaller ones.
For sake of argument how long does a high speed 3000 or 3600 RPM generator lasts as compared to a 1500 or 1800 one, I don’t think anyone will tell you the higher RPM ones last longer.

Wear goes up as a factor of the energy in the rotating components, and RPM increases the energy greatly.
Structurally RPM isn’t the limiting factor, rotating assemblies are capable of insane RPM’s, it’s actually piston speed, a short stroke motor can turn much higher RPM than a long stroke one.

It’s not that Diesels like to be run hard, it’s that very often due to their low RPM and power output per cu in compared to say a car motor, they will tolerate being run near max output better, because max isn’t really usually all that high.

Run one pretty hard in surges if you will to break it in, be sure to run it real hard more and more often as it accumulates hours, and then once your certain the rings have seated, then you can baby it for a good long life. Don’t start out babying a brand new motor, you need to run it hard enough to seat the rings first. It’s cylinder pressure that forces the rings against the cylinder walls that seats the rings, and that pressure comes from a lot of fuel being burned and driving the pressures up as a factor of heat.
Engines are not powered by explosions, they are powered by the rapid expansion of air from the temp of fuel burning, explosions are called detonation, which will quickly destroy an engine.

But also wake one up gently, allow it to warm up slowly and once the oil temp is up, then you can throw the power to it if you like, and also allow it to cool down slowly before shutdown to prevent heat soaking, especially in a turbo motor.

But the normal way most all of us operate our boats is near perfect, most of us crank our motors up in neutral and bump the RPM to about 1000 or so and then go about getting the anchor up and stowed. That is a near perfect warm up in my opinion, then we usually go slow approaching an anchorage, stop, drop anchor and back down on it and leave the motor idling until we have the snubber set, and that’s about a perfect cool down, again in my opinion.