Under loading.

"relevant temperatures are achieved"

If oil temp is critical to long and happy low load engine life there are any number of thermostats that can be used to bypass the oil cooler for the desired temp.

An Auto style EGT gauge is east to install, and the newest are NOT critical to the sense wire length.

$ 112. or so free shipping.

GlowShift EGT Gauge - Amazon.com‎

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Steve DAntonio said:

In most cases, if your engine doesn't have a load % indicator, then you can rely, roughly, on % rpm of rated wide open throttle (WOT). For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load. Load and rpm curves are not superimposed on each other, they diverge but not significantly. Bottom line is the 75% number isn't terribly critical, it need not be exactly 75%, that's a figure I use to ensure the engine is loaded while on sea trials, for realistic temperature measurements.

Before doing any of this, however, make certain your engine reaches rated WOT under load. Ideally it should exceed this rated number by 20-40 rpm, i.e. using the above example 3030 would be ideal, which tells you the engine isn't overloaded (acutely, this can kill an engine far quicker than under-loading), and that your prop is properly matched to the engine. If your engine doesn't reach rated WOT rpm find out why, and propeller adjustment should be the last option. Before that check injectors, valve adjustment, fuel supply and exhaust back pressure. I've encountered excessive back pressure on vessels fresh from the builder, so don't rule that out on a new vessel. In many cases, a prop pitch reduction only masks other problems, and when this is done it essentially de-rates the engine, you aren't getting the HP you paid for.

Click to expand...

Sorry for the long quote. It it a pain to do on the iPad I am on.

Thanks again Steve. I am very interested in all of this stuff right now as I;
a) have no experience with Diesel engines beyond smallish sailboat diesels.
b) I have an offer on my first power boat and a survey coming up in a couple weeks.

I have a Cummings mechanic doing the mechanical survey and he will be able to check everything out but I am trying to glean as much info as I can in the meantime so I can try to better understand what the heck he will be trying to tell me.

dhays said:

I am still confused as to how to determine % Load. I know it isn't rpm but how? Is it the amount of hp being produced, i.e. If the engine is dated for 300hp and based on manufacturers curves show you are producing about 100hp is that 33% loading?

Click to expand...

Short answer, yes.

Assuming it is propped to reach rated wot rpm the prop curve shows the load vs rpm. As you can see it is very non linear. In fact the perkins chart above tells us it was calculated based on a 2.7 exponent. If you plot the curve
(rpm /wotrpm)^2.7= you will reproduce the prop curve. You can just plug that equation into google search and it will do all the work.

The above exponent is a guess by the maker and some use 2.5 to represent how the typical propeller loads the engine.
The best measure, unless you have electronic systems, is actual fuel used vs max fuel use.

Steve DAntonio said:

In most cases, if your engine doesn't have a load % indicator, then you can rely, roughly, on % rpm of rated wide open throttle (WOT). For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load. Load and rpm curves are not superimposed on each other, they diverge but not significantly.
.

Click to expand...

Our main engines do diverge significantly. If we ran at 75% RPM, we would be well below 75% load. On our generators with much smaller engines the difference between the curves is less. However, with any sort of a performance chart and fuel consumption chart it's easy enough to approximate the load.

Edit:

I just quickly looked at our data on several engines, all on planing hulls. Interesting as our maximum cruise target is 80%. So, 80% load is the following percentages of RPM. 87%, 89%, 88%, 89%, 88%, 88%, 92%, 88%, 90%.

Steve D wrote;
"For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load."
Steve tell us this is a typo.
I have a 3000rpm engine and consider it 50% loaded at 2300rpm.

manyboats said:

Steve D wrote;
"For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load."
Steve tell us this is a typo.
I have a 3000rpm engine and consider it 50% loaded at 2300rpm.

Click to expand...

I can't believe he wrote that. Taking the same engines I did above, at 75% RPM here would be their loads:

% Load at 75% RPM: 51%, 48%, 50%, 52%, 51%, 52%, 47%, 55%, 52%.

That is a huge difference and, in my opinion, running at those loads would not be an adequate sea trial. Hopefully, he'll correct himself.

BandB said:

I can't believe he wrote that. .

Click to expand...

Elementary issue with self anointed experts. Once again, it illustrates need to pick your information sources carefully. Which is why many of us go to engine maker, boat diesel and proven hands on (issue specific) yards and mechanics.

That's a low one Tom.

"self anointed"?
I believe it was PMM that "anointed" Steve. But he was probably well anointed before that.
I have high regard for him.
But then I'm probably self anointed.
Sounds like a religious high.

manyboats said:

That's a low one Tom.

"self anointed"?
I believe it was PMM that "anointed" Steve. But he was probably well anointed before that.
I have high regard for him.
But then I'm probably self anointed.
Sounds like a religious high.

Click to expand...

Wifey B: Is "self anointed" a form of masturbation?

Greetings,
Mental masturbation...

RT Firefly said:

Greetings,
Mental masturbation...

Click to expand...

Stretching the definition of mental there RTF.....

I explained it more than several times before. Unfortunately, that's more than enough.

Greetings,
From an outside source: "
There is a world of difference between the load under which an engine is operated and the load factor for which it is rated. The same engine may have 3 or 4 load factor ratings and just suggesting that a certain percentage of instantaneous load is what a boater should aim for is.....(expletives deleted). Polite translation-incorrect.

Any engine that is normally operated at 1/5 - 1/10 of its rated output would be a great candidate for very short operation times before oil changes

Oil is cheap, engine rebuild/replacement is seldom cheap.

With the 200 hours of annual operation , 4 oil changes rather than 1, might take decades to spend on oil what an engine refresh would cost.

So, I don't get this angst about not working a Diesel engine. Truck drivers often sit in truck stops 12 to 48 hours idling their engines just to have AC. In my own trucking company our engines almost always reached 1 million miles, sometimes more. And think of the cases when the same drivers idle their trucks in the winter for heat.

Apologies, that was a typo, it should have been 2850 (and this is an unforgiving group, self-anointed, ouch), however, the point remains the same and I should have emphasized this in an earlier post. The reason for the 75% load figure is to simply ensure the oil and combustion chamber temperatures are optimized. I've chosen that number based on hundreds of sea trials I've undertaken, all of which have included oil and exhaust temp measurements (as well as throttle position, another critical figure when evaluating prop match), on vessels whose instruments included %load. In some cases I have been able to achieve similar readings lower load, but not always, and it depends very much on the vessel, hull shape and engine. More often than not, however, the 75% load figure achieved the goal I was seeking.

Therefore, please don't fixate, and I take the blame for not making this clearer, on the exact loading or rpm, the goal is to heavily load the engine. Again, a 3000 rpm WOT engine run at roughly 2800 will raise combustion and oil temp to the levels that minimize the formation of soot, varnish and sludge. Some cruisers do this by running at 100% throttle, however, I don't believe that's necessary routinely, although you should do it seasonally to ensure the cooling system is working properly, as 75% load achieves the desired goal. Most engine manufacturers provide graphs that show load at rpm, if you have access to one for your engine then that will definitively tell you at what rpm you reach 75% load.

Steve

My intemperant riposte aside for which I apologize, this under loading issue seems a bit like a red herring for our small trawlers. With the thousands of trawler engines out there and most loafing along at low power settings why are the shops not filled with glazed pistons and rings?

Diesel mechanics that are true experts like Ski could tell my self anointed a$$ I'm wrong but IMHO under loading is a non issue in comparison to engine malfunctions with cooling systems, fuel systems and tanks, exhaust systems/elbows, starters, alternators, batteries/associated electrics and hoses.

In fact I've never heard yards or mechanics fretting about glazed rings in a propulsion engine only on TF and dock talk.

FF said:

Any engine that is normally operated at 1/5 - 1/10 of its rated output would be a great candidate for very short operation times before oil changes

Oil is cheap, engine rebuild/replacement is seldom cheap.

With the 200 hours of annual operation , 4 oil changes rather than 1, might take decades to spend on oil what an engine refresh would cost.

Click to expand...

FF,
Best idea I've heard in a long time. A by-pass on the oil cooler would help too IMO.

Steve D Antonio,
I think you may be overstating your case a bit thinking you may not get you're point across unless you do. I do that on TF ... a bit of shock and holy cow gets attention when cold hard facts or old opinions go over the top.

75% load is a lot more load than many here would do even breifly. There's probably a lot here that have never been to WOT. I agree w you. We should load our boats about like a 36 Chevy going 55 or so down the road. Work to be sure and a bit hard but nowhere like scream'in. I think for many you should be a light to emulate but I do agree w those that know that all engines aren't the same. My old Perkins 107, my fairly new S4L2 Mitsu and a new high tech engine are indeed different.

I REALY like your avatar.
Eric

JDCAVE said:

Thanks Ski. Your experience in this matter gives me piece of mind. Once at operating temperatures, I normally set my Lehman 135 at 1800 and leave it there for the most part, and that gives me 7.5 kts. I rarely go above 2,000. WOT is 2650, I beleive, and according to one of the engine surveys I have, this indicates the boat is properly propped.


Jim
Sent from my iPad using Trawler Forum

Click to expand...

Yes, thanks Ski, but then I wasn't worrying about it.

Pretty much no matter how I run it, the Lehman (SP135) last last longer than I.

I used to run, 1600 to 1800 rpm, but my range now is 1500 to 1700, solely based on economics. The 100 rpms, raises speed about 8%, but consumption about 25%.

And I only use "military power" when I find myself in the wrong place at the wrong time as then I don't notice the noise

Richard

A friend of mine recently sold the last 42 made, he was first owner. It had a NA 6068 which just loafed along at 1800 RPM or less its entire life. You know how easy the 42 hull is driven, doubtful it spent its life at more than 35% M2 (132 hp @ 2400 RPM) load power rating. At time of sale it was nearing 7000 hours and passed inspections just fine.

Best you pull your pistons and check for glazing before you get vessel to PNW.

Steve DAntonio said:

Apologies, that was a typo, it should have been 2850 (and this is an unforgiving group, self-anointed, ouch), however, the point remains the same and I should have emphasized this in an earlier post.

Click to expand...

Was this entire section a typo then?


One of the entire points on this subject was that one cannot use % RPM as % Load. They are very different and in most cases % load is significantly less than % RPM.

It just seems like you misspoke, which we all do at times. Then just say you did. Clearly the 2250 wasn't a typo in the context of the paragraph it was in as it is 75% of 3000.

I'm not an expert, don't claim to be, I'm not published, don't have my own website to display my expertise, know very little about diesel engines compared to most here, but I know enough to know how seriously wrong that quoted section was and that entire premise of using % RPM.

Perhaps self-anointed was a bit strong, but when you do hold yourself out to be an expert, then the burden of accuracy and knowledge is higher than on the rest of us.

Greetings,
Mr. BB. Well said. I could expand on your thoughts but I don't want to be relegated to "scraping paint" as some who have been a bit more outspoken.

Steve:

I think that your 75% power loading rule of thumb is way off base.


Many here on TF have Lehman 120 or 135 engines or Perkins 135 engines. According to your rule of thumb you would have to run them at about 2,400 rpm to make 75% load. I will bet that no one here runs their engines that hard.


Most run below 2,000 rpm and Wxx3 above runs his as low as 1,500 rpm or about 30 hp (less than 25% load) with no problems.


And on the other end of the spectrum, how long do you think that the Yanmar 6BY 3.0 liter, 260 hp engine will last making 195 hp at 3,600 rpm or more than 1 hp per cubic inch of displacement? That is like running your BMW at 120 mph all day long on the Autobahn to keep it "loaded" at 75%.


David

djmarchand said:

Steve:

I think that your 75% power loading rule of thumb is way off base.


Many here on TF have Lehman 120 or 135 engines or Perkins 135 engines. According to your rule of thumb you would have to run them at about 2,400 rpm to make 75% load. I will bet that no one here runs their engines that hard.


Most run below 2,000 rpm and Wxx3 above runs his as low as 1,500 rpm or about 30 hp (less than 25% load) with no problems.


And on the other end of the spectrum, how long do you think that the Yanmar 6BY 3.0 liter, 260 hp engine will last making 195 hp at 3,600 rpm or more than 1 hp per cubic inch of displacement? That is like running your BMW at 120 mph all day long on the Autobahn to keep it "loaded" at 75%.


David

Click to expand...

We have a Yanmar 4BY3 in a RIB. WOT is 4000 RPM, 75% load is 3500 RPM and gives us a speed of about 35 knots. We use the boat as a tender, not to cruise so run to that load perhaps 10 minutes out of 4 to 5 hours. I should point out that ours is 180 hp vs. the base engine of 150 hp, so 75% load on ours is equal to 90% load on the basic engine.

This comes back to manufacturers recommendation and use of engine. Plus for those engines that haven't been run over a certain load for the last 30 years, I'd definitely not recommend suddenly seeing how they would do.

We also vary speeds. I'll pick one boat that it's recommended cruise by the builder and engine manufacturer is 65-70% load. This is a load to be run for hours and hours. I would say we run it something like this:

100% load, 1% of the time
80% load, 4%
65-70% load, 50%
30-65% load, 25%
15-30% load, 15%
Under 15% load, 5%

The point is that every engine on every boat has different most appropriate loads under which to be run.

I don't think Steve's 75% is off necessarily. On a performance boat we'd do that. But it's a generalization that isn't right for all situations. As to a Sea Trial, I'd definitely run up to and beyond the 75%.

It seems to me that if you can develop full rated RPM with your power plant given the prop and weight in operation of your boat, the best way to look at engine loading is over time. Since you typically calculate engine load not as a percentage of rpm but of fuel burned over time (GPH) versus the fuel burned at full rated RPM. My 420 Cummins 6CTA develops nearly 2700 rpm at WOT. The Cummins data sheet says at WOT it should burn 24 GPH. Over a 900 mile trip, based on fuel burned and engine hours, I used fuel at a rate of 2.5 GPH. I would put that at 10.4% loading. Typical cruise RPM was between 1250 and 1350. It seems in this situation loading as a percentage of RPM doesn't work out mathematically unless fuel burn is a linear function which according to the manufacturer's graph it isn't. Once the turbo starts to generate boost pressure at about 1800 rpm fuel consumption starts to climb on a steeper slope. According to the fuel curve, I would reach 18 GPH (75% loading) at 2300 RPM. 75% of maximum rated RPM would be 1950.

All this doesn't really matter since I still plan to run most days at 1250 to 1350 RPM as I am into long range not the extra 3 or so knots 15 GPH would get me. I will do some temperature profiling of the motor with an IR heat gun just so I know where it is operating. Nobody complains about my wake now. At 10-11 knots I will definitely get noticed.

Tom

Wxx3 said:

I used to run, 1600 to 1800 rpm, but my range now is 1500 to 1700, solely based on economics. The 100 rpms, raises speed about 8%, but consumption about 25%.

Click to expand...

I run my 2 DD 8.2's at either 10kn or 17kn, about 90% of the time. That will determine their loading history, which becomes moot, as I see it.

tpbrady said:

I It seems in this situation loading as a percentage of RPM doesn't work out mathematically unless fuel burn is a linear function which according to the manufacturer's graph it isn't.

Click to expand...

I've yet to see a situation where it does work. Every one I've seen RPM % is higher than load % except at WOT. The margin between them gets smaller the closer to WOT you get but even at 75 and 80 % load there's still a significant difference.

Following are the calculations for my engine at the desired cruise speed of 7.5 knots. According to the manufacturer we should expect 15,000 to 30,000 hour engine life with proper maintenance, although I would be at the lower end of that scale. Even 15k hours should last me the rest of my lifetime. The engine will still have about 25% reserve power, which is less than the mainstream way of thinking of course (see thread "Total and Reserve Power").

BTW, this works out to 2.2 hp per cubic inch displacement.

SISU 49CTIM PERFORMANCE at cruising speed, based on a 2.7 PROP LOAD curve
Note 1: Engine rating class A = constant full load

makobuilders said:

BTW, this works out to 2.2 hp per cubic inch displacement.

Click to expand...

That ratio seems very high, what CID and what HP rating?

sunchaser said:

That ratio seems very high, what CID and what HP rating?

Click to expand...

It is 4.9 liters, 300 cubic inches, 180 hp max rating.