In search of the 80% power setting

[North Baltic sea]

Originally Posted by rgano

I have no idea what curves you are looking at, but they surely are not the ones from my engine's manual. Look back at the PROPELLER power curve numbers I quote, and look again at the curves of the 6LPA-STD from the engines maintenance manual. At 3000 RPM I am taking a mere 120 KW of the available 220 KW. This engine is loafing at this 54% power setting. Come on guys, it's not rocket surgery. It's just fun with numbers in a fun hobby.

This yanmar page, i thel cranksaft Kw and you write tehority propel out put and i dot no what is your gearbox and propel, therefore crankshaft readig ...


If you have these facts known, why are you asking for clear things?

https://www.yanmar.com/media/global/...2datasheet.pdf

NBs

[Nomad Willy]

Originally Posted by FlyWright

Sometimes you just have to feel the boat to see what's the right power. Each boat has its sweet spot. Step away from the numbers and listen to your boat. You'll find the sweet spot.

“Sweet spot”
What can that possibly be other than a low vibration rpm.
And engines could care less about vibration.

Maximum power output should have to do w pressures and heat and other related things. All about engineering and nothing to do w feelings and sweet spots. IMO

[BandB]

So, you don't want to run at 80% load, then don't do it. Modern set ups actually give you load information. Otherwise you just go by % of fuel flow for an estimate. Your engine manual says 2800 to 3600 RPM but they don't say you have to run it at that or have to run at 3600 RPM. 3600 RPM is probably about 80% load. Our boats have best cruising speeds between 65% and 78% of load, based on actual performance charts we've made. I would not run constantly at 3600 RPM but would be comfortable running within the recommended range with occasional 3600 RPM for a few minutes. I'd on rare occasions run at 3800 RPM to insure I'm still getting peak RPM.

[Nomad Willy]

I’m quite sure when they say run at 2800 to 3600 they are giving a lot of slop to the prop loading issue. 2800 to 3600 could mean 65% to 85% load. Lots of leeway so it means little.

[North Baltic sea]

Here is my tug and cummins qsb 5.9 380hp, max rmp 3000 and about 2700 rmp 80% load. Load% varies slightly throughout time, due to waves.


I can not say where that 80% load my Cummin means, enybody knows?


Link to video

[Lepke]

If you run at 80% of hp your engine probably will go double or even triple the hours between overhaul compared to wot. The whole point is keeping the exhaust gas temperatures down. In most makes and models of diesels, EGTs should remain below 1200°F. Basic aluminum melts at about that temp. While steel and cast iron melt at about double that temp, metal degradation and wear start to happen at 1200° to 1250°F in long runs. Oil doesn't lube as well at extreme temps. That's based on heavy duty engines, not recreational grade engines that use smaller castings and cheaper alloys. Turbos at max hp can turn 100,000 rpm and burn the oil in the bearings.
A pyrometer is the best indicator. But you shouldn't need a pyrometer unless you're running a commercial engine at near rated hp continuously. Like a tug on a long tow.

[bayview]

North:

Here is the calculation of your prop curve using a 2.5 exponent. I am curious how well it fits at other RPMs


(2710/3000)^2.5=0.77556837258

[High Wire]

Yanmar 6LHPA has a continuous rating at 3680 rpm. Find the NMPG peak rpm under that and you're good IMHO. Fastest speed for the least fuel/load. Every boat is different and the engines don't know what boat they are in. If there is no peak, then your favorite sweet spot. There is no magic number where say 3400 is bad but 3399 will run forever. Every moving part in an engine wears at a different rate. No doubt they all wear on a exponential curve. Obviously more power equals more wear.
I remember that 80% thumbrule from the 70's USCGAux Boating Skills and Seamanship class. 70% for gas. Broad guidance for those that would otherwise run WOT all day until their engines blew then need a tow.

[markpierce]

I reach maximum (hull) speed at 2200 RPM (with 80 HP JD) at 72% power (actual vs. maximum fuel consumption). Going to 2400 RPM (engine's maximum: 4 GPM) does nothing but increase fuel consumption. Can run at max. boat speed all day, but that increases fuel consumption by 100% for only one knot increase of speed compared to an efficient 1800 RPM.

[Screaming04]

As the proud new owner of a JD 6068T that has 18,000 hrs without a rebuild, cold starts instantly and has zero blowby, I'm cured of the "80%" and "400 off the top" myths. This engine was run at about 50% wot or 33% continuous duty rated load for 21 years by the same owner. Keel cooler flow was restricted to maintain engine temps.

I'm of the opinion now that running lower rpm hurts nothing as long as you're in the recommended operating temp range.

[Irish Rambler]

Kiss, keep it 200 rpm below max rpm BUT, remember to change rpm every hour, slack it back a bit for 10 mins then back to cruising, give it some welly for 10 mins then back to your cruising.
With meticulous servicing your diesel will see you under the sod before it finally rings down FWE..

[DavidM]

Originally Posted by Screaming04

As the proud new owner of a JD 6068T that has 18,000 hrs without a rebuild, cold starts instantly and has zero blowby, I'm cured of the "80%" and "400 off the top" myths. This engine was run at about 50% wot or 33% continuous duty rated load for 21 years by the same owner. Keel cooler flow was restricted to maintain engine temps.

I'm of the opinion now that running lower rpm hurts nothing as long as you're in the recommended operating temp range.

David

[Nomad Willy]

Originally Posted by Screaming04

As the proud new owner of a JD 6068T that has 18,000 hrs without a rebuild, cold starts instantly and has zero blowby, I'm cured of the "80%" and "400 off the top" myths. This engine was run at about 50% wot or 33% continuous duty rated load for 21 years by the same owner. Keel cooler flow was restricted to maintain engine temps.

I'm of the opinion now that running lower rpm hurts nothing as long as you're in the recommended operating temp range.

“50% wot or 33% continuous duty”
Meaning 1/2 of the throttle stick movement?
33% of what for continuous duty? Could be less accurate than dock talk.
And lower rpm means little compared to lower load.
And coolant temp is controlled by the thermostat so why restrict the flow?

If running at 33% of max fuel burn one would be much better off indeed. I’ve broached the possibility that just removing the oil cooler would get the oil temp up higher and that is probably much more beneficial than artificially controlling the coolant. But good idea about getting the “engine” temps up.

So your engine seems fine at 18K hrs. But that dosn’t assume that it could be even better if the engine had run at 50-60% fuel load. Just say’in.

I prefer to run at 50% fuel load but it’s just my opinion.

[Screaming04]

By 33% load I mean 33% max fuel burn. 50% wot rpm means 50% max Rpm. Max rpm for the 154hp continuous duty is 2400 he ran at 1200. I’m guessing 50hp.
Engine runs 20 degrees cold without restricting keel cooler flow.
What a warm welcome.

[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.

[Lepke]

Cummings, Detroit, Cat main engines usually are not troubled by constant running at low rpms. West Coast salmon trollers often ran 12-14 hours continuously at just above idle. Tuna jig speed is about 1/2 throttle also for the whole day. In the late 70s, early 80s there were many boats with WWII surplus diesels that had never been overhauled.
At lower speed a diesel doesn't run as efficiently, but so much fuel is saved at lower speed, it's not noticeable.
I had keel coolers on my commercial fishing boats. They're usually a little oversize to cover all water temp conditions. They usually have a valve to restrict flow so the incoming coolant isn't too cold for proper engine operation.

[BandB]

Originally Posted by sunchaser

prime design range (provided oil and water temps are OK) of 1500 to 1800 RPM.

Where did you come up with "prime design range" and how did you decide it was 1500 to 1800 RPM?

[guy with a boat]

Originally Posted by Screaming04

What a warm welcome.

Welcome to TF. Don’t be bothered by the grumpy old men. They generally mean well even if the delivery can sometimes use some improvement.

[sunchaser]

Originally Posted by BandB

Where did you come up with "prime design range" and how did you decide it was 1500 to 1800 RPM?

The Cummins 5.9 has a huge population of genset applications. Gensets in this size operate at either 1800 - 60 hertz or 1500 - 50 hertz RPM. The gensets get most often parked in a trailer and are expected to run trouble free for many thousands of hours. So they have a starting design use as gensets at that specific RPM.

Longevity is paramount. Fuel consumption is closely monitored. Some engines get sent to the scrap heap because they're fuel hogs in genset use. Rebuild ease is essential with overall life before throw away expected to approach 30,000 or more hours.

The 80 to 150 kW range is very popular and competitive with about half a dozen other brands competing. This is where the 5.9 shines, genset duty at 1500 or 1800 RPM, it's prime design RPM range. At these RPMs, %operating time, warranties, achieved reliability and front end costs tend to rule purchase decisions.

[BandB]

Originally Posted by sunchaser

The Cummins 5.9 has a huge population of genset applications. Gensets in this size operate at either 1800 - 60 hertz or 1500 - 50 hertz RPM. The gensets get most often parked in a trailer and are expected to run trouble free for many thousands of hours. So they have a starting design use as gensets at that specific RPM.

Longevity is paramount. Fuel consumption is closely monitored. Some engines get sent to the scrap heap because they're fuel hogs in genset use. Rebuild ease is essential with overall life before throw away expected to approach 30,000 or more hours.

The 80 to 150 kW range is very popular and competitive with about half a dozen other brands competing. This is where the 5.9 shines, genset duty at 1500 or 1800 RPM, it's prime design RPM range. At these RPMs, %operating time, warranties, achieved reliability and front end costs tend to rule purchase decisions.

The one in the Genset is designed for 1500-1800 RPM but at moderate loads, certainly not over 80% load and probably not over 70%. However, the design criteria for the propulsion models is not the same as that for the gensets. I think you're stretching it to call that prime design range for the marine propulsion engines.