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Old 06-06-2020, 05:47 PM   #21
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My N46 with a Lugger, dry stack, when we brought it down from Long Island and outside, we ran it WOT 12 to 24 hours a day and night. The only problem was, it would approach ‘over temp’ so we’d cut back a bit on the throttle until the temp returned to normal. This started about mid FL. Everything was boiled out (keel cooler and engine).... so I attribute to the temp of the FL water. I did like the Lugger. I was your basic engine, nothing fancy or electronic, it worked or didn’t work and it always worked.
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Old 06-06-2020, 08:38 PM   #22
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Checking your engines at WOT is an important diagnostic tool. It starts with doing so the first time to make sure the engines and boat are performing as they should. You should exceed the rated RPM at WOT if you're running with very light load, typically 50-75 RPM. It's also a means of checking the two engines against each other if you have twins. If you can't hit that max RPM, something is wrong. It can be many things and the props are just one. However, if you're over-propped, you're over-propped and that doesn't just impact you at WOT. It may be you run low enough RPM that it doesn't significantly impact you, but if you run at 70-80% load then it could cause issues.

Now, once you have everything set, occasional checking at WOT is a quick and easy way to find out if something has changed. You may quickly identify what has changed, perhaps a dirty bottom, perhaps damage to props, perhaps engine just not performing. But this is a means of quantifying before and after and targeting work to regain what was lost. We consider no engine maintenance to be complete without a WOT check.

Perhaps this is more important to us because of the speeds we run, but I think it's more likely we'd just notice it more quickly. If you're losing 5% whether you're fast or slow, you still have an inefficiency.
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Old 06-07-2020, 09:30 AM   #23
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Thanks for all the help guys. I might add that the survey was done in late Sept. so maybe the bottom was a little dirty and reason for not hitting the 2800 rpm.
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Old 06-07-2020, 09:47 AM   #24
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An engine is overloaded throughout it's operating range if over propped. That is, it is working harder to generate X amount of RPMs no matter the value of X. It's like lugging your car engine at various speeds. For some insight into this, here is one article from a respected source.

https://www.sbmar.com/articles/engin...ngine-loading/
https://www.sbmar.com/articles/engine-life/
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Old 06-07-2020, 10:12 AM   #25
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Originally Posted by caltexflanc View Post
An engine is overloaded throughout it's operating range if over propped. That is, it is working harder to generate X amount of RPMs no matter the value of X. It's like lugging your car engine at various speeds. For some insight into this, here is one article from a respected source.

https://www.sbmar.com/articles/engin...ngine-loading/
https://www.sbmar.com/articles/engine-life/
Sorry, that's just not true. Modern engines with electronic fuel injection control, often have a gauge that shows percentage of load for that specific RPM. My engine is way over propped (not all by choice). Yet, when cruising at 7 knots, the percentage of load for 1,500 RPM is between 45 and 50%. Further, the installation met John Deere's warranty requirements as the engine computer tracks time above 80% load. As the dealer explained it to me, you can prop the engine to reach WOT, but if you have an engine failure as a result of towing stuff, they won't warranty it. Their warranty considerations are partially based on your percentage of time above 80%, regardless of RPM. The computer will record loads in excess of 100%. They can look at the computer to see how you operate or abuse the engine.

Ted
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Old 06-07-2020, 10:20 AM   #26
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Sorry, that's just not true. Modern engines with electronic fuel injection control, often have a gauge that shows percentage of load for that specific RPM. My engine is way over propped (not all by choice). Yet, when cruising at 7 knots, the percentage of load for 1,500 RPM is between 45 and 50%. Further, the installation met John Deere's warranty requirements as the engine computer tracks time above 80% load. As the dealer explained it to me, you can prop the engine to reach WOT, but if you have an engine failure as a result of towing stuff, they won't warranty it. Their warranty considerations are partially based on your percentage of time above 80%, regardless of RPM. The computer will record loads in excess of 100%. They can look at the computer to see how you operate or abuse the engine.

Ted
Different manufacturers and engines have different requirements. IIRC, Cummins says that if it can't reach rated rpm under a few different conditions depending on the application, no warranty for you. And some engines are more sensitive to high loads at low rpm than others just by their nature.
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Old 06-07-2020, 10:56 AM   #27
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The engine is designed to be run at wot, not in gear, right up until it hits the governor. This is called high idle. Then the engine is designed to be run at wot in gear and should hit the governor or the limits of the running gear. Under load.

As to how long the engine is certified to run at wot, depends upon the rating of the engine. My Cummins is rated M1 which means it can run at wot for 24 hours, which is probably what it would do if it was attached to a pump or a generator. Another model of my engine is rated wot for 1 hour every 24. So no blanket pronouncements over wot for all engines.

Wot tells you if everything is running as the factory intended. All of the engine parameters should be within the limits set in the manual while at wot.

One of the main problems with wot is that the average boat owner babies their engines and rarely runs them wot, thinking for some reason that wot will hurt their engine, which is not true. The other issue is that wot is incredibly noisy and sounds like the engine will literally leap off its mounts. It probably won’t but the sound is overwhelming so many will not complete a wot test.

If something blows at wot, it was weakened or damaged already and would have let go under worse circumstances. This way it was found under “test” conditions.

A Lehman was not a success as a truck engine but it excelled in combines and generators where it would run 30,000 hours plus at wot, never or rarely shutting down.
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Old 06-07-2020, 11:06 AM   #28
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Check your tachs.
Then if still overpropped cut some off your props to raise the rpm (not rpms). Find a good prop man to determine where and how much to cut. There are guys bangíin on props and there are good prop men.
And if youíre overpropped wanting to know if itís too much think would it be too much if it was underpropped? In this case of 100rpm Iíd rather be 100rpm underpropped than 100 overpropped. I think all the variables would, over time, cause a lack of WOT rpm .. not an excess.
If the prop man thinks he can bring the rpm up to 2875 by removing 1Ēof pitch Iíd go that route. 2900 would be fine too as itís unlikely youíll ever gain WOT rpm. But you will loose rpm.

But I am no engineer. And most here would rather be 100rpm over than 100rpm underpropped. And your rated rpm is not a redline at all. Itís just the rpm that your engine develops itís maximum power. Most engines can operate 3-400rpm over rated rpm, especially at lower loads. Talk to a good prop man or (best) an engineer.

Also if youíre going to run your engine at 30% load or less all the time disregard my post and just run it like it is.
Doesn't the idea behind getting 100 RPM over WOT spec apply more to a boat in relatively light load with the idea that the WOT under the inevitable later increased loading will sag somewhat?
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Old 06-07-2020, 11:16 AM   #29
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If I read the post right he had a lot of load in that boat. I really don't see where hundred or 75 RPM deserves much attention
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Old 06-07-2020, 11:29 AM   #30
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If I read the post right he had a lot of load in that boat. I really don't see where hundred or 75 RPM deserves much attention
Kinda where I was headed.....
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Old 06-07-2020, 11:33 AM   #31
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Different manufacturers and engines have different requirements. IIRC, Cummins says that if it can't reach rated rpm under a few different conditions depending on the application, no warranty for you. And some engines are more sensitive to high loads at low rpm than others just by their nature.
Absolutely understand that different manufacturers have different warranty requirements. That's why I didn't make a blanket statement. Guess JD is more realistic in this regard.

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Old 06-07-2020, 11:46 AM   #32
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The engine's governor controls RPM rate and limits maximum RPM, assuming sufficient fuel and air flows are available.
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Old 06-07-2020, 05:53 PM   #33
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High idle term

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Checking to see that the engine revs up to its "high idle" speed (wot, no load, in neutral) is to confirm that nothing else is limiting rpms, like not hitting the throttle stop, governor malfunction, etc.

Then with that confirmed you can check the wot rpm under load with a phototach or a phototach calibrated dash tach. If the engine is not reaching the rated wot rpm then the engine is under too much load and it should be reduced by cleaning the bottom or a prop adjustment if it is clean.

David
Sorry David not picking on you specifically but Iím seeing this constantly throughout the form and was using it as an example. Was wondering why do people keep using the term high idle to describe max no load rpm. High idle is either a term used to diagnose a problem with an engine when you cannot get the engine down to its rated idle speed or an option or setting on some diesels to run Small accessories off of a main engine while itís idiling and not under load such as alternators, air compressors or hydraulic pumps just to name a few since most of them are designed to run most efficiently at a certain rpm which is usually higher then a regular idle but no where near a max no load rpm. Btw Im certified to work on and have gone to specialty schools for Cat, Cummins, Detroit diesel, yanmar and mercury outboards( eh it was free so why not much prefer diesels) . Also when it comes to loading of engines Iíll just use this as an example since The manual for a ford Leighman is the last manual Iíve read and know it off the top of my head. Without getting too deep into things there are generally different ratings for engines such as max no load rpm, max load rpm, and max continuous load rpm. And there may or may not be some sort of overlap between them. A ford Leighman 120 has a max no load rpm of 2650 . Itís max load rpm is 2500rpm at 120hp and itís max continuous load is 2500 rpm at 114hp, so how you would read that is if you wanted to be able to use max rpm continuously you would need to have it slightly under propped so at 2500 rpm your propeller is only requiring 114hp from your engine. If you were trying to have it use all 120 hp at 2500rpm it should only be run at that load for a specific amount of time without any damage Or accelerated wear to the engine. That time is also generally specified in the manual, which it is not in the ford Leighman manual. Considering that it is not specified I personally would not use max load rpm for more than about 3 hours. That seems to be on the lower end for a time limit on those types of ratings but thatís just my oppinion on that, when it comes to a ford Leighman if an engineer told me less Iíd defer to his judgment. Also while on the same thing the max continuous hp rating would be 114 so That would mean if you have the propeller set up to load the engine to 120hp at 2500rpm the max continuous rpm would be at the rpm curve for 114hp.
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Old 06-07-2020, 06:34 PM   #34
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Your rated RPM should be hit while carrying your typical load. So saying 7 POB might reduce RPM is not correct . You should hit rated RPM with full fuel ,load and typical seas state.
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Old 06-12-2020, 01:34 PM   #35
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Dont over think it, the engine needs to be able to hit whatever WOT is stamped on it. It should be able to obtain that with whatever max load you think you might be carrying around.

If you cant hit that number, then have some pitch taken out of the prop then try it again. Dont talk yourself out of this by over thinking it.

Missing WOT by 100 or so rpm's wouldn't stop me from buying a boat, but I would get it fixed as soon as possible so I can move on to stressing about some other stuff.
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Old 06-12-2020, 01:43 PM   #36
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I have heard you guys post about the need to have your engines be ble to hit WOT. I obtained past survey data (for a boat I am considering) from 3 years ago. WOT for the CAT 3116 -300HP is 2800rpm. The survey says it hit 2700 for one engine and 2710 for the other engine. Fuel tanks were full and 7 people on board. This is a miss of about 4% on the rpms. Is this too far off and something to be concerned about or within the margin of error. It obviously didn't worry the current owner as he bought the boat. But what if it comes up the same on my survey? Thanks again.
Hitting WOT is done rarely. I wouldnít worry about a 4% under rev, specially if full fuel, and full boat. Another consideration could be a clean bottom and clean props.
Those could make the difference.
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Old 06-12-2020, 01:51 PM   #37
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Your rated RPM should be hit while carrying your typical load. So saying 7 POB might reduce RPM is not correct . You should hit rated RPM with full fuel ,load and typical seas state.
Thatís why Many say 50 to 100rpm over rated is ideal. Then when you do get the max load and bottom growth you may still not be overloaded w the lever ďon the pinĒ. Loads and growth are given variables on all boats. And they increase 10 times (or more) as often as they decrease.
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Old 06-12-2020, 04:17 PM   #38
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Actually for Cat 3116 engines with serial numbers beginning with the prefix 4KG, 2800 is the max rpm you should see, ever. The governor which is built into the injection control will limit the rpm. The "high idle" speed (full throttle with the gear in neutral) setting should be 3075 rpm, per the engine data plate.

It sounds to me like the governor setting might be a little low, which is fine. I'd be more concerned with the cooling system. Can the engines sustain full power without overheating? Fouled heat exchangers and failed seawater impeller are common.

You want to be able to count on getting full power to outrun weather, for example.

I also recommend getting Caterpillar S-O-S analysis of both lube oil and coolant. That is the gold standard in determining engine condition

Also, be aware there is a service bulletin on 3116 and 3126 engines directing the use of MONO-GRADE SAE 30 or 40 line oil exclusively. All oil should be API symbol CF or higher.
Do NOT use multi viscosity oils such as Shell Rotella 15W-40. Caterpillar sells a product called SAEO which is blended for 3116 and 3126 engines. My Cat dealer sells it at the same price I pay for Mobil Delvac.

Good Luck! Feel free to ask questions - I've been working on Cat engines a long time.
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Old 06-12-2020, 04:48 PM   #39
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Interesting post so far, but I went back and read the original post - in summary on a heavily loaded boat, with unknown bottom and prop cleanliness, and engines of unknown age with tachs of unknown accuracy it was 100rpm short of its WOT. 4%?

I reckon those poor old engines need a bloody medal, not people suddenly ripping off their props and attacking them with a hack saw.

Yes I understand the importance of over and under propping but in this case I think its close enough for Government work (to quote a saying I learnt when living in the US)
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Old 06-12-2020, 06:20 PM   #40
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I usually agree with Ted and this is no exception. Those 300 HP. 3116 are great engines, I had a boat for 20 years with twins and had very few problems, biggest problem was a tiny hole in a fuel line that JB Weld took care of. My boat would hit the top RPM as long as it wasnít heavily loaded when heading to the Bahamas. Those few hundred RPMs never worried me.

Service the engines as needed and enjoy it.
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