Wide Open Throttle

bayview said:

The full load or max power curve indicates the peak output capability at various RPM.

I thought that any point on the curve would be OK and that was how engines were derated. Tony Athens specifically said no. Derated engines are rated at lower output than the max power curve of the highest output model according to Tony.

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We source a fair number of primarily Deere, Cat, and Cummins industrial engines, and the power, torque, fuel burn rate, and other curves are different for each HP rating of the same engine. Injectors, timing, possibly cams, and programming can vary depending on the power or duty-cycle rating. Look at John Deere 4045 power units, which vary from 80 hp to 173 hp, all rated at the max of 2400 rpm. I'd have to dig through paper files to find Cat C15 and C18 ratings for duty-cycle ratings from A through E, as they no longer put those details online.

But a C18 A-rated 'prime power' will run at full power all day and all night, while the standby E-rating has severe restrictions on percentage of run time at various loads and the uninterrupted time at those loads. But they have a much higher power rating for the same engine. They just won't last as long working like that. Which is fine for applications that don't require continuous output at those higher hp levels, but do require intermittent and infrequent high output duty cycles.

I don't know T. Athens, but I would say he's correct.

Tom.B said:

View attachment 77282

Here is the tag.

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My TAMD40A's WOT loaded and unloaded is the same, 3100 RPM but I would never cruise at 2900 RPM. Usually I want to be about 1600 to 1800 RPM. Its a comfortable sound level and 7 knots. WOT only gets 8.5 knots. Why waste the fuel? Every now and then I take it to WOT unloaded for maybe 20 seconds to see if anything has changed. I wont take it to WOT loaded again (did it once before I purchased it) because it smokes there.

This conversation is very different than it was 8-10yrs ago. Then few w FL’s were brave enough to run 1800rpm.
And most it seemed were overpropped and I think that is even changed more.

jimisbell said:

My TAMD40A's WOT loaded and unloaded is the same, 3100 RPM but I would never cruise at 2900 RPM. Usually I want to be about 1600 to 1800 RPM. Its a comfortable sound level and 7 knots. WOT only gets 8.5 knots. Why waste the fuel? Every now and then I take it to WOT unloaded for maybe 20 seconds to see if anything has changed. I wont take it to WOT loaded again (did it once before I purchased it) because it smokes there.

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That makes sense for displacement boats. We, on the other hand, are a planing boat. The difference in low and high make a huge difference in efficiency through the water. Our boating needs always has us balancing speed, time, and fuel burn expectations.

You should, however, run your motor at loaded WOT (or 200 below it) for a little while every time you’re out to prevent the muck buildup in the exhaust.

Andy has a great point about noise at WOT.

I have to admit, the first year I had the FL and ran it 2500rpm for 10-11 hours getting to montauk from NYC, I pulled into montauk lake, snuck up on the leeward side of star island, threw in anchor and cut the engine.

I broke out an MRE, sat on the back deck waiting for the MRE to heat up. It was so quite and beautiful with one exception, the ringing in my ears from the engine. I actually thought I hurt my hearing, lmao. I also developed a head ache. Lmao. No joke.

The following year I spent a ton of money sound proofing the hell out of the engine box. I put so much insulation I had to move the throttle, oil filter mounts and some other stuff so I could fit 2 inches of expensive sound proofing. It cut the noise by 50%. Well worth it.

Was just a great point Andy made about the noise, and a funny story for the post.

Just a heads up. I am replacing the alternator this week on my Lehman 120, so I called Brian from American diesel to get the alternator (nothing wrong with alternator, just wanted more amps to charge batteries). I am hoping to take pics and post in this section about it)

While in the phone I asked about WOT. He said that he would not suggest WOT for a big trawler, but said on a little boat like mine (26 foot Croverbuilt) that WOT is fine. Just FYI,

WOT for a big trawler...Never? Only to check engine health?

Sorry about not being clear. On a big trawler, he said that running WOT all the time like I do was not a good idea.

I did not ask about the specific durations of WOT and how long it’s acceptable. Just wanted to point out that in a 26 foot semi displacement hull like a Groverbuilt, WOT all the time is fine.

I go WOT for a minute or so fairly often to check fuel flow, cooling system and other functions. Been do’in that ever since running up the full throttle not long after we bought Willy caused the engine to quit. I wanna know if alls well down there and a short run wide open tells a lot.
But I usually run 700rpm down from WOT. 50% load on our FD boat. Rated at 3000rpm and we run at 2300.

psneeld said:

200 under max rpm is the cruising speed rpm rule of thumb for every commercial operation that I have worked with if they didnt have a specific one in mind.

Didnt always run there, but if we were trying to make a good time or distance we did.

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Those are commercial rated engines not pleasure rated high output per liter.

TomandJeri said:

We source a fair number of primarily Deere, Cat, and Cummins industrial engines, and the power, torque, fuel burn rate, and other curves are different for each HP rating of the same engine. Injectors, timing, possibly cams, and programming can vary depending on the power or duty-cycle rating. Look at John Deere 4045 power units, which vary from 80 hp to 173 hp, all rated at the max of 2400 rpm. I'd have to dig through paper files to find Cat C15 and C18 ratings for duty-cycle ratings from A through E, as they no longer put those details online.

But a C18 A-rated 'prime power' will run at full power all day and all night, while the standby E-rating has severe restrictions on percentage of run time at various loads and the uninterrupted time at those loads. But they have a much higher power rating for the same engine. They just won't last as long working like that. Which is fine for applications that don't require continuous output at those higher hp levels, but do require intermittent and infrequent high output duty cycles.

I don't know T. Athens, but I would say he's correct.

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Tom: Do I understand correctly that while both high and lower rated engines have the same WOT RPM that if I over laid the max power curves the lower rated engine curve would be lower that the high rated engine at all RPMs?

bayview said:

Tom: Do I understand correctly that while both high and lower rated engines have the same WOT RPM that if I over laid the max power curves the lower rated engine curve would be lower that the high rated engine at all RPMs?

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In a nutshell, yes. I'm looking at an old QSK19 brochure for mining applications (Tier 1) right now, since it was the first one in my legacy engine file, and the curves are grossly different for the 450 hp w/ peak torque@ 1500 rpm on up to 800 hp w/ peak torque @ 1500 rpm, though the rated hp is at higher rpm generally for the higher hp versions, but not always. The curves do have a different shape, though, and aren't just extended to higher rpm for higher hp rated engines.

In the case of the 4045 T3 Deere engines, they all have max hp at the same rpm. I glanced at an intermediate hp unit, too, and it also peaked at the same 2400 rpm.

http://uploads.gocdn.us/52/314/4045HF485_173_2400[1].pdf

http://uploads.gocdn.us/52/198/4045TF280_80_2400[1].pdf

These aren't marine specific engines, but it demonstrates the concept that the curves vary with rated power within the same engine model, and that they're not just limited in rpm. At least the engines I deal with mainly work that way.

bayview said:

Those are commercial rated engines not pleasure rated high output per liter.

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But it was used also when running recreational boats for a Marine Max dealership.

Most people dont think anything of it.

Seems like many things discussed here are ultra conservative.

Sure owners tend to be conservative because they want their engines to last.

Dealers are short term owners covered by warranty and want to show the best performance to prospective buyers. Boat show delivery skippers run fast as well.

Help on what WOT means for a gasser. I see lots of good info here on the diesels, but what about this engine. See pic. Manufacturer states WOT is between 5000-5400. Does this mean I am ok running this up to 5400 for a few minutes with no engine damage? I am not comfortable doing this, but what if a surveyor wanted to do this as part of sale? The most I've run this engine up to is 4000 RPM - at that RPM I am doing about 33 MPH on calm waters.

It should not hurt the engine to run WOT for a few minutes if there isn’t anything wrong with the engine. Don’t go over 5400.

They are giving you a range of WOT operation to help you choose a good prop.

At 5000rpm or less you run the chance of overloading the engine.
At 5400rpm I think they are calling this a max WOT just like we do in trawler land.

The range is probably there to accommodate typical props an owner might choose.

I ran into this when my 60 Suzuki was new. I think it was 5350 to 5800rpm.

On my Willard I loose/gain about 200rpm per inch of pitch change. My engine develops it’s rated power at 3000rpm. They could have said in the manual 2700 to 3000rpm to test props. There’s another engine speed above rated power and that’s where the governor limits higher engine speed. Kind of a red line. But in most diesel manuals for higher rpm they specify how long you can run at WOT (max).

But 5400 may not be the rpm that you can operate at WOT continuously. I’ve not seen continuous operation gas engine specs. But I think using 5000 to 5400 is mostly to test props. I’d say if you have a clean bottom use anything between 5000 and 5400 should be what you can achieve at WOT. I would try to get a prop that would run up to 5400. If you had a big load on your boat you will get a lower WOT rpm. Lets say you get 300 less w extra fuel and 5 people aboard. If you propped to 5000 rpm and then loaded up your boat you’d only be turning about 4700. That may not be good. I personally like to prop a bit light so as dirty bottoms and lots of people onboard come into play your engine will be happily singing along positively not overloaded.

But Mark if your going 33mph at 4000 maybe at 5400 you’d be running 43mph. The engine dosn’t care how many mph the boat’s going. It just cares if it’s being over rev’ed or over loaded. You probably don’t know what your rpm never to exceed speed is. But I’m guessing if you prop your boat so max WOT gives you 5000 to 5400 you will not be able to overe’rev your engine.
Think of this;
They recommend you running up to 5400.
They recommend you run at 5000.
I read they recommend running anything less than 5400 at WOT.
But what you run continuously would probably be somewhere between .... I decided I really shouldn’t say .. and couldn’t say. Perhaps max continious engine speed is specified by intake manifold manifold vacuum. That would very nicely take into consideration load.

Go to the engine manufacturer for more information.
Not mechanics, sales people or people like me and others “on the dock”.

Thanks for great info. This is one of those B3 outdrives with twin counter rotating props. The props are the ones that came from Sea Ray factory. 43 mph on a 7700 lb boat - I am not sure I want to go that fast - Sea Ray says the boat will do 41 mph so your calcs are accurate. When we put this boat for sale next year I've been reading surveyor reports and they like to run the engine through its paces, and I didn't want to do something stupid��

Do you have closed cooling or raw water cooling? One of the main issues with WOT testing is engine overheating. That is one of the main reasons to do it, to find out if the engine will overheat or not. I would recommend you do it before the survey and sea trial to see how it goes. Go through the whole boat and look for issues that the surveyor will look for and fix them before they become an issue.

The cooling is raw water intake exhaust is underwater through the outdrive. Ok once I get her back from annual maintenance I will run her up to 5000 and see what happens. Having it still under warranty is nice for peace of mind. Thx.

If it is still under warranty then it is the time to give it a WOT run for at least 5+ minutes, it it craps the bed under warranty is the time to find out. Good luck.

On the advice of my VERY knowledgeable mechanic, who has been taking care of my misc. diesels for like 20 years, I run my FL 135 (32' GB) up to max throttle (2450 in my case) every few months for maybe 10 minutes. First, this should never damage the engine unless there is already something really wrong with it--in which case it's better to find out about it now. Secondly, I do this to slightly stress the engine systems under somewhat controlled conditions, rather than having a surprise problem many miles from home. Usually, the coolant temp rises a little bit, but not enough to set off the alarm. Once the temp did go up enough to set off the alarm, then came back down soon after I came back to cruiising rpm of 1800. Turned out the heat exchanger needed cleaning, no big deal. So yes, running the engine up to WOT once in a while is a just good maintenance procedure.
Oldersalt
"Everything on your boat is broken. You just don't know it yet."

Oldersalt said:

On the advice of my VERY knowledgeable mechanic, who has been taking care of my misc. diesels for like 20 years, I run my FL 135 (32' GB) up to max throttle (2450 in my case) every few months for maybe 10 minutes. First, this should never damage the engine unless there is already something really wrong with it--in which case it's better to find out about it now. Secondly, I do this to slightly stress the engine systems under somewhat controlled conditions, rather than having a surprise problem many miles from home. Usually, the coolant temp rises a little bit, but not enough to set off the alarm. Once the temp did go up enough to set off the alarm, then came back down soon after I came back to cruiising rpm of 1800. Turned out the heat exchanger needed cleaning, no big deal. So yes, running the engine up to WOT once in a while is a just good maintenance procedure.
Oldersalt
"Everything on your boat is broken. You just don't know it yet."

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I agree!

Just ran our mains WOT for 4 minutes over the weekend, temps were good. 69GPH not so much.

The rooster tail and wake would have made for jet ski heaven!

Oldersalt wrote;
“On the advice of my VERY knowledgeable mechanic, who has been taking care of my misc. diesels for like 20 years”

Mechanics are for replacing parts, troubleshooting, estimating repair costs and other mechanical doings.
When you want engineering information including performance limitations you need an engineer or a manufacturers representative that has close (preferably) working experience w engineers.
Mechanics are for bending wrenches but many are very experienced in their trade. Some have a great “gift of gab” that makes them appear to be much more knowledgeable than they are.
Be especially cautious if you hear a mechanic promote things that are spelled out clearly in the manual with different numbers or practices not spelled out in the manual.
If you can’t get the information you need from the manual contact the manufacturer. 9999% of the time you will get the correct and best information.

My boat's maximum speed is achieved at 2200 RPM (normal cruise at 1800) while the engine (John Deere 4-cylinder, naturally aspirated, 80-horsepower) is capable of a wasteful fuel-consumption 2400.

Nomad Willy said:

Oldersalt wrote;
“On the advice of my VERY knowledgeable mechanic, who has been taking care of my misc. diesels for like 20 years”

Mechanics are for replacing parts, troubleshooting, estimating repair costs and other mechanical doings.
When you want engineering information including performance limitations you need an engineer or a manufacturers representative that has close (preferably) working experience w engineers.
Mechanics are for bending wrenches but many are very experienced in their trade. Some have a great “gift of gab” that makes them appear to be much more knowledgeable than they are.
Be especially cautious if you hear a mechanic promote things that are spelled out clearly in the manual with different numbers or practices not spelled out in the manual.
If you can’t get the information you need from the manual contact the manufacturer. 9999% of the time you will get the correct and best information.

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So are you advocating not listening to his mechanics advice? He has trusted him for 20 plus years... Do you listen to Hattons advice or are you thinking they are trying to sell you parts on the engine you purchased? Hatton mechanics trying to rip you off?

I agree with doing a brief (a minute or 2 is plenty) WOT check every few months. Confirming that it comes up to the expected RPM and temperature doesn't climb excessively is a good check. If you see an issue on the WOT test, it's an indicator that something isn't right, even if it's not bad enough to show up otherwise yet.

markpierce said:

My boat's maximum speed is achieved at 2200 RPM (normal cruise at 1800) while the engine (John Deere 4-cylinder, naturally aspirated, 80-horsepower) is capable of a wasteful fuel-consumption 2400.

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Why are you overpropped Mark?
Trying to save a bit of fuel?

Years ago I usta downshift when slowing down or coming to a stop.
I suggested that my mother do the same.
She thought about it and said; “what’s more expensive engines or brakes”?
As you can see .. mom was smart and I was a young kid.

In the overpropping issue I’d rather do what is best for my engine. The tiny bit of fuel one saves from overpropping is fly stuff compared to engines.

Actually the best way to slow down a car is to take your foot off the gas pedal a bit sooner and save both the engine and the brakes... And in our motorhome I use the exhaust brake absolutely as much as possible since I really don’t want to buy a brake job in it.