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Old 05-01-2012, 07:34 AM   #21
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Going to "high idle" is a standard test on diesels of the size we use. Yes it is somewhat scary the first time you do it, at least it was for me.

I remember when I repowered my old Mainship in 2000 with a brandy new Cummins 6BTA , I had just finished getting power to the starter so I cranked it up and it was running maybe 5 minutes as I was checking for leaks, etc.
The sales/tecnician guy from the Cummins distributor shows up to see how my install is going. First thing he does is say "let's see how this thing checks out", and runs it up to high idle and checks the rpm with a hand held. "3050. Perfect" he says.
Kinda scary the first time.
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Old 05-01-2012, 09:13 AM   #22
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C lectric's, Eric's and Jay's responses should be bookmarked for the next inevitable "no, no not full RPM in neutral!" or "should I prop for full rated RPM?" diesel engine discussion. Nice to have experienced hands on board.
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Old 05-01-2012, 09:43 AM   #23
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My 120 lehman would reach only 2200 in neutral or in gear still running great after the 1500 hrs I put on it
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Old 05-01-2012, 11:04 AM   #24
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C lectric,
I think the newer outboards have "rev limiters". Seems to me my e-tec Evinrude book says something about that. Do you know about that?

jleonard,
I thought it was just plain crazy (like Art) and was very nervous the first time I did it. The engine was new too.

Tom,
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Is 30 the length of your boat or your age? Must be your age as the boat looks longer. You could fix that problem you describe but some people (like FF) like to overprop. It's sorta OK if you NEVER run your engine anywhere near is rated power and rpm. I'm guessing you run at 1500-1600rpm. It would probably be bad to run that engine at 2000.
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Old 05-01-2012, 11:14 AM   #25
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Motion 30
There are lots of vessels out there where the throttle stops limit RPM to say 85% of full rated RPM, Good thing too. Many of these vessels are over propped and if they were run at full rated RPM would overheat and or suffer from too high EGTs. Tony Athens had a response to this same question today on boatdiesel regarding re-powering an old Chris Craft.
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Old 05-01-2012, 12:55 PM   #26
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Have never heard of this on a marine engine...if it's rated at xxxx rpm...that's what it is rated for if properly propped/loaded when you push the throttle to full (properly adjusted).
Now the question is..what rating...diff manufacturers call it diff..but if it's continuos duty (commercial) or intermittent (pleasure craft) etc..etc... the the "rated" rpm is usually lessened and governed so.
If that's what you mean..then I agree...
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Old 05-01-2012, 01:51 PM   #27
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Interesting Discussion

My Detroit's are rated at 2800rpm. My high idle is set at 2300rpm digital tachs. My full rpm in gear is 2300rpm. I surveyed two 48's with Detroit's both were set identically. Hull speed for is reached before max rpm @1800rpm. I was told by my mechanical surveyor this was ok and probably set this way as full rated power was not needed. What say you?
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Old 05-01-2012, 04:26 PM   #28
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Tom,
Thanks

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Is 30 the length of your boat or your age? Must be your age as the boat looks longer. You could fix that problem you describe but some people (like FF) like to overprop. It's sorta OK if you NEVER run your engine anywhere near is rated power and rpm. I'm guessing you run at 1500-1600rpm. It would probably be bad to run that engine at 2000.[/QUOTE]

The boat with the lehman was a MT 34 , and yes cruised around 1650rpm she is sold now, new boat has 3208t would love to have twin 120s
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Old 05-01-2012, 05:03 PM   #29
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You're very right psneeld and usually in your owners manual the continuos limitations are laid down. I think for my Mitsu it's up to an hour at WOT. Do'nt remember what the max continuos limitations are but I think it's 2800rpm. I'd run it at 2800 all day long but I'd either look at the book or just not run continuos above that. One needs to keep in mind that if you're 5% down in rpm you're prolly at least 20% down on load/power. My engine has an industrial rating of 37 hp at 3000. Vetus markets a marineized version at 42 hp and Westerbeke sells the exact same engine at 44 hp.

Scary,
I'd say it's not right as you do'nt know how you're propped. You may be quite overpropped and have no way to know. Without the governor you may top out at 2400.
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Old 05-01-2012, 05:54 PM   #30
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Sometimes you can't reach WOT due to excess back pressure on the exhaust.
Nothing to do with the prop. Before re propping I would check that first.

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Old 05-01-2012, 11:10 PM   #31
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Scary,

I think what you have was done most likely by Hatteras. Indicated by the fact that two others you found were setup the same.
Also that your book says rated rpm is 2800 so, to me, there has been some customizing.

Your boat is a full displacement hull or nearly so built to be an economical seakindly boat at hull speed, not planing or semiplaning.

Hatteras used the DD because they were good strong engines capable of operating many thousands of hours with decent service and servicing.
However, Hatteras realized the engines were capable of producing much more power than the hull could use so there is a limiter somewhere to prevent engine abuse and wasting large amount of fuel.

Hatteras could have asked DD to modify the injection pump and reduced the rating but I think, can't say for sure, that if done by DD, DD would have left a RATED and a HIGH IDLE that were different. The fact that your APPARENT rated and high idles are the same tells me the throttle is limited somewhere by a stop.

You can check if you wish but since your hull likely cannot use any more power there is no point other than just to know. They apparently left you with somewhat more power than the minimum to move the boat at hull speed to account for head seas or winds. Good and I'd be surprised if that were not so.

With this setup Eric has a point that you could be overpropped and not know it. If the engine had been derated by DD and a new rated and high idle left then you could use those differences to determine propping suitability. With a stop the governor could feed more fuel than the engine can use at that max rpm if the load is too high. The best way to monitor is the use of a pyrometer and watch for high EGT in your case.
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Old 05-02-2012, 07:05 AM   #32
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"Hatteras could have asked DD to modify the injection pump and reduced the rating but I think, can't say for sure, that if done by DD, DD would have left a RATED and a HIGH IDLE that were different. The fact that your APPARENT rated and high idles are the same tells me the throttle is limited somewhere by a stop".

2 stroke DD are set to the power required by the injectors.

They (the injectors) ARE the injection pump.

The proper technique to reduce engine power on a DD is to install an engine with fewer cylinders.

That way they all work at over 60% , so the efficiency is high.

Probably the add dept nixed the more rational/efficient engine choice .

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Old 05-02-2012, 11:06 PM   #33
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Interesting comment

[QUOTE=FF;85206]"Hatteras could have asked DD to modify the injection pump and reduced the rating but I think, can't say for sure, that if done by DD, DD would have left a RATED and a HIGH IDLE that were different. The fact that your APPARENT rated and high idles are the same tells me the throttle is limited somewhere by a stop".

2 stroke DD are set to the power required by the injectors.

They (the injectors) ARE the injection pump.

The proper technique to reduce engine power on a DD is to install an engine with fewer cylinders.

That way they all work at over 60% , so the efficiency is high.

Probably the add dept nixed the more rational/efficient engine choice .

QUOTE] The 58 lrc was available with the 4-72 and the 6-72 so there you have it. Most west coasters preferred the 7-72 over the 4-72 for the wave conditions on the west coast. I believe there are a few 48's with 120 hp Lehmen's so Hatteras must have felt 120hp was the right amount of power. I don't use anywhere near that cruising.
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Old 05-09-2012, 10:01 PM   #34
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Bottom and prop condition also affect whether a mill will reach theoretical WOT under load particularily when the vessel is geared and propped to be at or above hull speed at WOT, and does not have an abundance of horsepower, meaning enough to bring the boat on a semi plane.

Secondly most modern diesel manufacturers recommend 'racing' the engines as well as a limited amount of time at WOT under load as maintenance practices for the fuel injection system, the high engine rpm and load removing combustion residues from injectors as well as breaking carbon deposits from ring sets.

I can not speak for Lehman engines, but this is the case for Cat and Yanmar. In the vessel cited above, a 48 LRC Hat with dual 120 hp engines would not be able to push itself very far up the bow wave even at WOT, thus hull growth and prop condition would definitely affect hp demand and impede attainment of theoretical WOT under load.
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Old 05-09-2012, 10:30 PM   #35
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"mill"???
You mean engine?
I have'nt heard that expression since I was a teenager.
Are yiu a teen ager?

What's "theoretical" WOT? WOT is WOT.

One dos'nt gear/prop to achieve a boat speed......you gear/prop to achieve a specified engine speed that insures a certain engine load. Whatever the boat goes the boat goes.

"racing" engines for recommended maintenance? Interesting approach. Sounds like it could have merit though.....if the engine was loaded correctly.

"Growth and prop condition" is usually considered maintenance.

Sounds like your'e from another planet. Florida.....oh I see.....you are from another planet. Being from Alaska (at the moment) it seems that way anyway.

Interesting comments Tim and I believe there are many here that speak for and against Lehmans.
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Old 05-10-2012, 06:39 AM   #36
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Quote:
Originally Posted by manyboats View Post
"mill"???
You mean engine?
I have'nt heard that expression since I was a teenager.
Are yiu a teen ager?

What's "theoretical" WOT? WOT is WOT.

One dos'nt gear/prop to achieve a boat speed......you gear/prop to achieve a specified engine speed that insures a certain engine load. Whatever the boat goes the boat goes.

"racing" engines for recommended maintenance? Interesting approach. Sounds like it could have merit though.....if the engine was loaded correctly.

"Growth and prop condition" is usually considered maintenance.

Sounds like your'e from another planet. Florida.....oh I see.....you are from another planet. Being from Alaska (at the moment) it seems that way anyway.

Interesting comments Tim and I believe there are many here that speak for and against Lehmans.
Funny...I understood what he was saying....unfortunately there really isn't better standardized "terminology" with engines through the years. My Lehman manual calls it "gross power" xx hp at xxxx RPM....never heard it referred to that before that manual. So his use of WOT was what the manuf. says you get at the pins whereas others know WOT is what you get at the pin. Certainly we all agree that growth loads up the engine and may reduce the recommended max RPM...and a vessel engined near it useful power versus overpowered suffers speed while all will suffer fuel burn.

Many of the higher speed, modern diesel manufacturers recommend so many minutes of max throttle if you have been underloading them for long periods...some I have heard /read recommend it at the end of the day no matter what...just to make sure.

Mill???? hear it every once and awhile...but not like yesteryear...maybe more aviation oriented because I don't hear it as much since I've been away from aviation..
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Old 05-10-2012, 12:02 PM   #37
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psneeld,
I remember "mill" as a slang term used by hot rod guys and wanna be's. In car magazines too but have no idea if it's used today.

It does sound like tinb7734 is into faster boats. That's fine......I'd rather go twice as fast as I go in Willy.

And yes .....lots of trawler guys never ever run their engines at full or near full power. They think ther'e engines are going to fly apart or somth'in. But if they are over propped it's just as well. But they need to find out. Under propped a little (50 - 100rpm) is fine too as far as I know but I think running at WOT for brief periods is most valuable as a test to learn that nothing performance wise has changed. But MOST importantly it needs to be done as a step to insure a boat's engine is correctly matched to it's load......the propeller and gear ratio. When I first bought Willy (w her original Perkins) the engine ran perfect until I opened her up and after about a minute the engine quit. We need to know if our "mills" are there for us to perform at 100% or more importantly to know if there is something wrong.
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Old 05-10-2012, 12:56 PM   #38
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Quote:
Just a little deuce coupe with a flat head mill
But she'll walk a Thunderbird like (she's) it's standin' still
She's ported and relieved and she's stroked and bored.
She'll do a hundred and forty with the top end floored
She's my little deuce coupe
You don't know what I got
(My little deuce coupe)
(You don't know what I got)
I think this is the only time I can remember someone referring to "mill".
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Old 05-10-2012, 01:49 PM   #39
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Quote:
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psneeld,
I remember "mill" as a slang term used by hot rod guys and wanna be's. In car magazines too but have no idea if it's used today.

It does sound like tinb7734 is into faster boats. That's fine......I'd rather go twice as fast as I go in Willy.

And yes .....lots of trawler guys never ever run their engines at full or near full power. They think ther'e engines are going to fly apart or somth'in. But if they are over propped it's just as well. But they need to find out. Under propped a little (50 - 100rpm) is fine too as far as I know but I think running at WOT for brief periods is most valuable as a test to learn that nothing performance wise has changed. But MOST importantly it needs to be done as a step to insure a boat's engine is correctly matched to it's load......the propeller and gear ratio. When I first bought Willy (w her original Perkins) the engine ran perfect until I opened her up and after about a minute the engine quit. We need to know if our "mills" are there for us to perform at 100% or more importantly to know if there is something wrong.
I think tinb7734 knows that and is saying you'll never get to WOT if you're all dirtied up..
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Old 05-10-2012, 01:57 PM   #40
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Interestingly: The word "Mill" referring to auto engines was a slang term used (and I think the term may have actually originated) in the clandestine distilleries’ "Booze Running" days... reason was... “Gin Mill" to bootleggers was a common term. The drivers took up the word in reference to their engines because they found that the engines performed even stronger if they added some of what they called the “high test” (98 proof or better) distilled alcohol to their fuel. Thus, they started a slang term, calling their engine their “mill”

How do I know this: Starting in 1976, at 6K ft. elevation in Sierra Nevada Mountains, for 7 years I was in construction partnership with a tough old boy named Ivan (and I do mean tough!). He and I became primary masonry and concrete contractors on an 18 hole golf course, octagonal Club House protruding out the side of a mountain cliff, and the adjacent 750 condominium project. Ivan was in his 60’s I was in my 20’s. He was the money and biz smarts, I was the estimator and job site ramrod. I learned a lot from Ivan. We together hired workers and had up to 50 on payroll in the best of times. Ivan and I became great friends and worked very well together, made lots of money, and shared many a drink and raucous night! To the point - -> Ivan had been a hot-rod driving booze-runner, back in his very young days! He told me many a story. The reason for calling the engines the Mill was one of them. Ivan would only run illegal booze in Chryslers because he said they were the fastest cars then on the road. In the 70’s and early 80’s he still would only drive Chryslers. He told me that things were in his favor in a road race with the cops with a Chrysler but that all changed when the cops got radios in their cars and he got nabbed because of that. He quit driving booze after that.
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