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Old 08-14-2012, 05:30 PM   #21
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When was the last time you had your boat at WOT.....................

The question is.

For how long and how often should you operate the engine at WOT.
1) This past May.

2) A couple minutes.

My boat's owners manual suggests running the boat at WOT occasionally to see if it still reaches the recommended WOT RPM (in my case, 3900). If it doesn't there's a problem that should be corrected.
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Old 08-14-2012, 05:55 PM   #22
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Ran up to WOT underload yesterday but only for 30" or so. Got 2100rpm with a slimy bottom. Usually get 2200rpm. The high idle for our particular engine is 2345rpm. In the case of older motors (Cats anyway),this figure is unique to each engine and is recorded on the data plate along with maximum power - 540hp at 2100rpm.
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Old 08-14-2012, 08:24 PM   #23
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Based on recommendations from Bob Smith at American Diesel, we run our FL 120 at WOT for about 5 minutes almost every time we are under way for a day. Bob recommends this as a regular engine check and the exercise the engine. It always seems to be happier after we do this. Chuck
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Old 08-14-2012, 08:29 PM   #24
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Based on recommendations from Bob Smith... It always seems to be happier after we do this. Chuck
Don't forget that he makes a living selling engine parts.

A freshly washed car always seems to run a little better too.
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Old 08-14-2012, 08:48 PM   #25
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Don't forget that he makes a living selling engine parts.

A freshly washed car always seems to run a little better too.
Yes but several other engine manufacturers say the same if you have been running at idle or low RPMs most of the day. I know after a day of trolling with my 3208 powered sportfish...she blew a lot of smoke upon first runup. after trolling.

Your thoughts on the pros/cons????
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Old 08-14-2012, 08:58 PM   #26
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The Cat 3208T in my Black Fin has a high idle of 3200 Max under load 2800 and max continuous 2600. I usually cruise at 2200-2400.
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Old 08-14-2012, 09:06 PM   #27
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When I repowered my old Mainship , Cummins (the distributorship)told me to run it up every time I was comming back into port. That was a way to make sure everything was up to snuff, and if something went wrong you were comming back to port anyway.
I didn't do that every time, but many times.
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Old 08-14-2012, 09:12 PM   #28
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Same for Perkins.

After extended periods of idling, recommendation is to run the engines at WOT under load, 2800 rpm in my case, for at least 10 minutes prior to shutting them down.

I'm an advocate for following the manufactures recommendations. There are too many boat yard mechanics out there, with "Urban Legend" information they're only to happy to pass on.

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Old 08-14-2012, 09:20 PM   #29
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Same for Perkins.

After extended periods of idling, recommendation is to run the engines at WOT under load, 2800 rpm in my case, for at least 10 minutes prior to shutting them down.

I'm an advocate for following the manufactures recommendations. There are too many boat yard mechanics out there, with "Urban Legend" information they're only to happy to pass on.

LB
Yes but a lot of sharp boatyard mechanics fixed problems that the manufacturers barely stood by through the years...

Good and bad on both sides. Hard to know who to trust sometimes.
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Old 08-14-2012, 09:24 PM   #30
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Good and bad on both sides. Hard to know who to trust sometimes.[/QUOTE]

--------------------------------------------------------

That is exactly my point. . .
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Old 08-14-2012, 09:28 PM   #31
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Good and bad on both sides. Hard to know who to trust sometimes.
--------------------------------------------------------

That is exactly my point. . . [/QUOTE]

But you made it sound like blindly following manufacturers recommendations was where it was at.
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Old 08-15-2012, 02:51 AM   #32
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Ran my JD at 1800 RPM for several hours recently, and near the end of the run, opened the throttle wide momentarily to reach maximum-governor-regulated RPM of 2400 (engine rated for maximum of 2500). This time the engine had a hard time reaching 2400 and the engine "bounced" between 2200 and 2300. Felt like a fuel-supply problem, solved by switching between the two Racors. Time to change that filter!
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Old 08-15-2012, 06:06 AM   #33
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Yes but several other engine manufacturers say the same ...

Your thoughts on the pros/cons????
Probably can't hurt much, probably doesn't do much other than burn off the oil and stuff that condenses in the cold exhaust manifold.

Marin might be a bit overly conservative in his approach but it works for him and it avoids the condition where a problem is most likely to occur, during acceleration or deceleration. An engine is less prone to mechanical damage if it operates in a steady state condition, steady speed, steady load, steady temperature. It is when the hardware is stressed by acceleration, temperature changes, and increasing or decreasing load that a failure is most likely to occur.

Marin's description of his mentor's advice is sound, it falls under the "local knowledge" umbrella. Sometime the user base learns things about an engine that the manufacturer didn't or couldn't predict. If the user base is large enough and old enough the users figure out what to do and what not to do.

Marin's often mentioned P&W 985 is a great example, there have been many improvements to that engine based on user experience and it serves them well. The users and caregivers of those engines may be a bit more technically sophisticated than many recreational boat drivers but that doesn't mean that the collective experience of Lehman (or other engine) owners and users is not worth considering.
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Old 08-15-2012, 06:31 AM   #34
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Full throttle no load should probably be checked (15 seconds) each year on comissioning.
With a warmed up engine. It is a problem finding tool.

Running on the pin underway should cause no hassles for 10min every so often also as a check ,10 min will find any problem.

A realistic high cruise is down 10% (in RPM) or usually 300 rpm down from the RPM found on the full throttle in gear.

EG engine 2700rpm no load, 2500 full tilt underway , 2200 rpm is your get home , damn the fuel burn or wake speed.

"High Idle" is a special condition used on coaches and some machinery to operate heavy loads like an air cond unit .

I have never heard the term used to describe the no load gov setting.

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Old 08-15-2012, 09:17 AM   #35
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"High Idle" is a special condition used on coaches and some machinery to operate heavy loads like an air cond unit .

I have never heard the term used to describe the no load gov setting.

FF
It's in my Cat manual.
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Old 08-15-2012, 01:34 PM   #36
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It is also called high idle by Cummins.
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Old 08-15-2012, 01:51 PM   #37
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Marin might be a bit overly conservative in his approach but it works for him and it avoids the condition where a problem is most likely to occur, during acceleration or deceleration.
I'm sure I do take a more conservative than "normal" approach to operating engines. But fixing them is expensive, or if I do it myself a time-consuming pain in the ass, and replacing them is even more expensive. So my objective in operating an engine--- any engine--- is to maximize its service life and the time between when something has to be fixed or replaced.

That's not to say I don't use them as they are designed to be used. I use the full rated manifold pressure in the radial when I take off, I drive my car at 70 or 80 mph when I can. But I don't ask more of an engine than I actually need to accomplish something.

I consider myself very fortunate that I have been in aviation and boating at the tail end of what I consider to be their "golden ages" in terms of the people in it. Guys like Bob Munro who started Kenmore Air Harbor and did more with floatplanes--- both flying and fixing them--- than most other men in the same business. On the boating side, it's been people like Bob Lowe who founded the Grand Banks owners forum and who made a successful career as a shipwright and boatyard owner fixing, restoring, upgrading, and maintaining boats like Grand Banks, wood and glass. And our acquaintance in the UK who became an absolute master at diagnosing, fixing, and overhauling diesel engines.

These were people who did what they did through common sense, an inherent ability, self-reliance, and who worked at at time when one was required to do a lot on their own. Bob Munro was a brilliant seaplane pilot, but he was also a brilliant powerplant mechanic. Whatever happened to his plane during a flight he could fix when he got back. Or on the spot if necessary. As opposed to people today who are forced down a limiting path by countless regulations and requirements and with whom the attitude is often "it's someone else's problem." I have learned to have a tremendous respect for these "old guys" because today, when they say something having to do with their field of expertise, they are almost always right even if it flies in the face of the armchair theorists.

This WOT topic comes up from time to time on the Grand Banks Owners forum. Bob Lowe had a response fairly recently that has stuck with me so I went back and found it. Here is what he had to say in response to a member who advocated taking the engine in his GB to WOT for five minutes every time the boat was run. ---------

"The purpose of the WOT runs is to stress test the engine components for weakness. Same as when you go to the doctor and he puts you on the treadmill and stresses your heart. Of course, some people have a heart attack while doing the stress test.

"My personal opinion is that I do not want my boat to have a heart attack when I am out cruising so I make sure to properly maintain those components that can fail, such as raw water pumps, water pump, fuel pump, and so on and make sure to change oil and filters as needed and maintain the cooling system, hoses and belts to keep the engines in top condition. I believe that is the best insurance against premature failure.

"The added wear and tear of the WOT runs may give one confidence that the engine is in good condition, but is it worth it if it also stresses the engine components to near failure and results in premature failure?

"Just as I don't go to a doctor for stress tests on my heart to satisfy his curiosity, I don't do stress tests on my engines to see if they will fail. Instead, I try to keep all components in top condition and I also carry plenty of spares to fix any but the most severe failures."
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Old 08-15-2012, 02:14 PM   #38
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Bob Lowe had a response ...
"The purpose of the WOT runs is to stress test the engine components for weakness."
I don't necessarily agreee with that. If the manufacturer rated the engine to produce 99 horsepower continuously, then it is designed to be run that way 24/7 until it wears out. If it is rated at 110 for 1 hour out of 24 and 99 for the other 23 then it can be used that way.

If WOT delivers the rated ouput or less and is within the specs there is no valid reason to self-impose some other restriction based on docktalk. There may be real world conditions such as Marin mentioned with the Minimec fuel pump but that one seems to be related to frequent speed and load changes, not continuous operation.

The question was "For how long and how often should you operate the engine at WOT?" The answer is as long as the manufacturer says you can run it at that power or until you get tired of buying fuel. Operating at rated output is not conducting a "stress test." That has already been done in the manufacturer's test cell so he could develop the charts you need.
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Old 08-15-2012, 02:36 PM   #39
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You're correct, but..... The issue, at least for me, is not will an engine run continuously at WOT but for how long? Absolutely, it can run at rated power 24/7 until it wears out but in the case of a powerplant like an FL120, that "wearing out" is going to occur pretty soon if it's run that way. As opposed to going 12,000 to 14,000 hours in recreational boat service given proper operation, servicing, and maintenance, which is the reputation that particular engine has when it's run in the 1500-1800 rpm range.

Engine manufacturers all provide the maximum rated power of the engine, but I've only ever had two owners manuals say that "this engine is rated at x hp continuously for y period of time."

The radial in the airplane I fly is rated for full power (450 hp) for exactly one minute. If you don't back the power down to METO (Maximum Except Takeoff) or less at that one minute mark, all bets are off as to the longevity of the engine. In the Cessna 206 I used to fly, its Continental IO-520 was rated at 300 hp for five minutes at which point the power had to be backed off. In both cases these limitations are spelled out prominently in the operators manuals.

But there is nothing in our FL120 manual that says how long the engine can be run at maximum power. So it's a crap shoot if you choose to operate that way. You can do it, but I suspect you will soon be on the phone to Bob and Brian Smith at American Diesel.

As to newer engines, I'm sure they can do it, too, for at least as long as the warranty is in force.
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Old 08-15-2012, 02:37 PM   #40
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A friend of mine is a mechanic. For Chrysler.

the engine computer has an ap that records the ammount of time a diesel truck is used as it is intended.

There is seldom greater than 2% of the time a diesel pickup actually is under load.

SD
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