In search of the 80% power setting

[North Baltic sea]

Originally Posted by sunchaser

Baltic
There are thousands of Cummins 5.9 owners out there that are quite content to run their engines at 1500 or 1800 RPM. They do this day and night for tens of thousands of hours running at a continuous 110 or 130 or so HP. They are called gensets.

Fuel burn on these 5.9 units is about 5 to 6 gph. So here is my question Baltic, do you see any harm in running your engine at it's prime design range (provided oil and water temps are OK) of 1500 to 1800 RPM for long periods other than it results in a slow boat.

Hi,

I almost time i run 850-1350rmp of my tug (load 30% in that rmp area) qsb works fine and the heat remains normal

This yars I cruised 2580nm, from time to time about 50nm i run fast 6 months period ...

Here in Finland fuel costs US $ 5.8 / gallon and slowly driving I can run at 6-5 nm / gal vs. 12-15kn 1.15 nm / gal, one of the reasons why I bought NT was the ultimate fuel economy vs. the boat size.

If runs quickly i drive that 80% charge for about 15kn, because of the same liters / nm for a period of 12-15 kn.

(sory my bad English)

NBs

[Ski in NC]

Consider also that the 5.9 (and now 6.7) Cummins B motor is used extensively in pickup and medium duty trucks. A pickup driving at 70mph on a highway trip unladen typically gets 20mpg (3.5gph) and runs around 1500rpm. That's about 65hp. These engines are rated at around 300hp-350hp so highway cruising is nowhere near 80%. Even lower load putt-putting around town. Known to run easily to 500k miles, which at an average speed of 40mph, that's 12,500hrs.

Not too far from what trawler duty cycle looks like to the engine. Engine does not know what it is pushing, it just knows it is supposed to turn fuel into spin (and heat and noise!!). Truck, boat, gennie, whatever.

Lots of things to worry about with these boats. Engine duty cycle is very low on the list. It will do what you ask it to do. If duty cycle is reasonable, it will not harm the engine.

[Nomad Willy]

When talking about percentage of load in boat engines turbocharged and NA engines aren’t IMO apples and apples.

If you had an engine that was NA and was rated for continious duty at 2200rpm propped to rated hp and the guy in the next slip had the same engine w a turbo the turbo at 2200rpm would generate far far more heat and would be generating much more hp. But probably using the same con rods, crankshaft, bearings and most other parts most likely excluding exhaust valves and perhaps rings.

So the typical dock talk “3-400rpm down” may not apply. One needs to consult the manual for such information. However if you had a 6-354 Perkins and your friend had a 6-380 Ford you could probably assume they were very close in all respects including continous rpm rating. However one could still have sodium filled exhaust valves so checking w the manufacturer still would be a very good idea.

But most NA engines are probably quite similar as in approximately 300rpm down from rated rpm propped right. It would be interesting to me to see how turbo engines compare to NA engines. Especially those using the same base engine.

[sunchaser]

Eric

Those are good points. It would be interesting to know if pistons, rods, cranks, valves etc are the same whether for a 330 HP Cummins or a continuous duty rated version of the 5.9.

Take the very popular Cummins 5.9 rated at 330HP. The manufacturer states the engine should be run no more than one hour out of eight at full throttle or 2800 RPM. Total marine engine hours no more than 300 per year. As Ski notes, this is the case for marine propulsion or light truck duty.

OK, that same 5.9 block (?) can be used for continuous (prime design RPM) duty at 1800 RPM but limited to 120 to 180 HP dependent upon aspiration and fueling design.

Similar ratings for continuous duty gensets or water pumps(1800 RPM) are done by JD, Cat and Perkins for engines in this size range. I do know that for Perkins Sabre the engine innards are the same whether for continuous at 146 kW or lighter duty at 170 kW (up to 4000 hour per year) such as ferry or commercial fisherman service.

So for Baltic, running at hull speed or in his case 1300 to 1500 RPM, the engine will last "forever." Not so the engine hang ons though where marine age knows no % load.

[Nomad Willy]

Sunchaser,
This question of continious rating has been in my mind a long time .. for no paticular reason though.

For the 5.9 does that mean continious at WOT or just at that rpm?

IMO any of the diesel engines we have here on the forum should last forever given no overloading and good maintenance. But continious rating (propperly loaded) is another issue. But most diesels should be fine 5 or 10 minutes at WOT. And many are probably good for 1/2 hr or so. But most boats are so overpowered that even WOT for any period of time would be pointless except fot periodic engine check. I do WOT 2 or three times a year or to check a prop.

[Nomad Willy]

Ski wrote;
“Consider also that the 5.9 (and now 6.7) Cummins B motor is used extensively in pickup and medium duty trucks. A pickup driving at 70mph on a highway trip unladen typically gets 20mpg (3.5gph) and runs around 1500rpm. That's about 65hp. These engines are rated at around 300hp-350hp so highway cruising is nowhere near 80%. Even lower load putt-putting around town. Known to run easily to 500k miles, which at an average speed of 40mph, that's 12,500hrs.”

Huge difference Ski. Those truck engines accelerate, decelerate and most importantly climb HILLS.

[Ski in NC]

Originally Posted by Nomad Willy

Huge difference Ski. Those truck engines accelerate, decelerate and most importantly climb HILLS.

And if you kick your trawler engine up to higher power setting once a day, you are climbing a hill too!!

[ranger58sb]

Originally Posted by Nomad Willy

Huge difference Ski. Those truck engines accelerate, decelerate and most importantly climb HILLS.

But then they coast down the other side, too...

-Chris

[markpierce]

Aren't engines rated for higher continuous service are detuned versions with lower power settings?

https://www.morganscloud.com/2016/10...s-mean-to-you/

[Nomad Willy]

Originally Posted by Ski in NC

And if you kick your trawler engine up to higher power setting once a day, you are climbing a hill too!!

Yes I mostly agree. But if it’s done I suspect that running it at high bell for at least 10min will be of great benefit but just running the rpm up for one minute to “blow-er-out” won’t be worth doing. Getting the temps up is the important element IMO.

But in defense of the trucks they climb 80 times as many “hills” as the boat engine. Just say’in the comparison is a bit weak.

Chris going down the hills IMO isn’t applicable to this issue.

[Nomad Willy]

Originally Posted by markpierce

Aren't engines rated for higher continuous service are detuned versions with lower power settings?

https://www.morganscloud.com/2016/10...s-mean-to-you/

Mark,
I think that’s what I’ve got and here’s why.
My engine is rated at 37hp by Mitsubishi .. probably some sort of industrial rating. Most of the Mitsu S4L2 engines go to generators and little front end loaders. General industrial use.
Vetus and Westerbeke offer the exact same engine but they rate theirs at 44hp (Westerbeke) and 42hp for the Vetus. All three engines were rated at 3000rpm. So in the case of the three Mitsus no difference in tuning was employed .. I don’t think.

[Irish Rambler]

Constant running for hours on end can glaze the bores and cause excessive oil consumption on some engines. This is the reason to stick to the manufacturers oil type/viscosity ratings and recommendations.
A turbo charged engine running at a constant low speed needs to be run at high speed for 20/30 minutes to raise the engine temperature and burn off carbon deposits from the turbocharger blades.
For a long working life every engine should be run at idle for 5 minutes after a hard run to dissipate hot spots in the engine block, this is especially important for turbo engines whether they are fitted in a boat/truck or car.

[Nomad Willy]

IR,
Never been better stated.

[psneeld]

Constant RPM forever doesnt seem to affect Lehman 120s thankfully.

[ranger58sb]

Originally Posted by Nomad Willy

But in defense of the trucks they climb 80 times as many “hills” as the boat engine. Just say’in the comparison is a bit weak.

Chris going down the hills IMO isn’t applicable to this issue.

My point was only that the comparison isn't all that great. 65 MPH downhill, no load... not much like typical marine constant propulsion situation.

On the idea of continuous ratings mentioned in a few posts... Our 3-cylinder Yanmar genset motor runs at 1800 RPMs and is probably rated to do that all day every day forever. The (almost) same motor in our home tractor runs at way more RPMs (no tach, but I'd guess 3000+) when implements are in motion, and the rating probably takes into account that nobody runs a tractor like that for more than 8-10 hours/day max. (A guess.) I'd also guess that engine would maybe rev even higher if ungoverned.

-Chris