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Old 10-08-2008, 08:23 PM   #21
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RE: Prop-pitch

Eric -

I think you're confusing old engines versus old designs that were intended for 10-20 khr TBOs in trucks tractors, pumps, and such - like the Lehmans and Perks.***

The Lehman "Super 135" and Perkins 6.354 are very similar - around 6 1/2 litres, 135 hp, 1300 pounds. redline 2400-2600.* With clean fuel, clean oil, and enough cooling water, there's probably not much you can do to hurt it.* Run it full throttle loaded down to 1800 RPM, or run it at 20% power for hundreds of hours and it'll just keep taking it.* These are NOT the engines that D'Antonio is preaching about.

Now look at the Yanmar 6BY260.* 260 HP at 4000 RPM, 200 continuous at 3600 RPM.* 3 litre displacement.** Weight is under 700 pounds.

Or the Cummins 4.2 EI 320.* 316 HP at 3900 RPM.* 4.2 litre displacement.* Weight about 1000 pounds.

These are lightweight, high RPM engines that are putting out a LOT of horsepower for their weight and displacement.* Probably a 2000 to 3000 hour TBO.* Overprop one of these, or run it at 20% power all of the time, and you've got problems.* They*have minimal margins.* These are what D'Antonio talks about.

They're a new breed of engine.**Better fuel efficiency, no smoke, but highly stressed and really not much different from gas motors in terms of their longevity.
*
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Old 10-08-2008, 09:29 PM   #22
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RE: Prop-pitch

Chris,
It's hard to imagine running an engine WOT 700 rpm down from max power rpm. Steve D didn't make any exceptions to his 75/75 rule. Perhaps he didn't want to mention it and stir up lots of complications. Since so many trawlers have engines like the 380 Fords and 354 Perkins the majority may be of this type and if so Steve should have addresed that side of his rule. My new engine seems to develop a bit more power ( I don't know how other than to say there's 35 years of new technology ) And the bore, stroke, displ, combustion chamber type and other design features are the same. I'd really like one of you guys on the PMM web site to ask Steve .. put him on the spot.

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Old 10-08-2008, 09:46 PM   #23
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RE: Prop-pitch

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nomadwilly wrote:

You guys say it's much less cause your engines are old. When my engine gets old can I under load too?
You're misinterpreting the use of the word "old," at least the way I'm using it. I mean old design, old technology, old metallurgy, and old operating philosophy (which influenced the design and construction of the engine). NOT old age.

The retired fellow I talked to in Ganges did more than work on thousands of these engines. He said he was also was involved in working with Ford to design improvements to the engines as operational problems surfaced over time. So he was apparently much more than just a shop mechanic.

Quote:
nomadwilly wrote:

Steve D didn't make any exceptions to his 75/75 rule.
From what I have been told about Steve D'Antonio, engine designs older than twenty-five or thirty years don't exist to him. Their technology and operating parameters are so different from modern engines that he doesn't even bother to consider them. I recall reading some article by him (not in PMM) in which he was talking about the proper way to operate and maintain a marine diesel. He acknowledged the old generation of diesels with one sentence--- something to the effect that "of course none of this applies to the old thumpers of the 1960s" or words to that effect.

So I am much more inclined to take the advice of a retired fellow (be it Bob Smith or the fellow I met in Ganges) who spent a career dealing with these engines in real service than I am a writer whose boating world is comprised of modern technology engines that are similar to the "old thumpers" that I have only in that they both burn the same kind of fuel.


-- Edited by Marin at 22:57, 2008-10-08
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Old 10-09-2008, 03:37 AM   #24
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RE: Prop-pitch

You guys say it's much less cause your engines are old.

The usual Ford marinization was like a car engine , it had a 100% rating , but was never expected to operate near it.

Industrial engine marinizations can be operated far far higher on the power curve , and retain good service life.

The industrial preferred load 80% max power at 90%- rated rpm is NEVER approprate for a car or tractor donor.

The Fords do well at 1500 to 1800 , because if you look at the prop curve only a small percentage of max power is required .

An advantage of a car or tractor donor is they are built to suffer far less at the low loads of their normal use.
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Old 10-09-2008, 08:02 PM   #25
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RE: Prop-pitch

Yeah, I agree with Marin (seems to happen a lot) about D'Antonio.* I won't restart the "let's rag on PMM" thread, but the comments still apply.

IMHO, for more serious powerplants discussion, go to boatdiesel.com and pay yer $25.* Tony Athens, Ski, and some of the other guys who moderate and frequent the forums live, work, breathe, and eat diesel.* Lots of good articles, and you can list the forums by engine or transmission type.

I wonder if D'Antonio ever pondered how that Nordhavn 40 they wrote the long article about made it around the world at 1200 RPM on its Lugger - about 35% power for a few thousand hours.* The Lugger - which is a Deere block - is a new engine but an old school design.
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Old 10-09-2008, 09:19 PM   #26
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RE: Prop-pitch

Did that Deere/Lugger suffer?. If not I'll throw in with ya. No glazed cylinder walls, smokin hard starting engine? Ya sure ? I'll quit ragi'n on you guys about the underloading issue. But what if the 75/75 rule applies to turbo engines ... if you backed down 200 rpm you'd probably be under 75% load. I think I'll find my heat gun and see how slow my engine needs to run to have lube oil thats too cool for healthy engine operation. It seems this loading issue is a huge grey area... different cyl walls ( honeing metalurgy ) different piston alloys, different rings ect ect. One thing I've forgotten about the 380 Fords .. they have a very low compression ratio .. 16-1 I think. I think all NA modern engines are over 20-1 yes? I won't buy into over proping though.

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Old 10-10-2008, 07:41 PM   #27
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RE: Prop-pitch

Quote:
FF wrote:

You guys say it's much less cause your engines are old.

The usual Ford marinization was like a car engine , it had a 100% rating , but was never expected to operate near it.

Industrial engine marinizations can be operated far far higher on the power curve , and retain good service life.

The industrial preferred load 80% max power at 90%- rated rpm is NEVER approprate for a car or tractor donor.

The Fords do well at 1500 to 1800 , because if you look at the prop curve only a small percentage of max power is required .

An advantage of a car or tractor donor is they are built to suffer far less at the low loads of their normal use.
FF, you should know that the industrial engines and their operating parameters are mostly due to the fact that they have been de-rated.* SO you build a big engine and rate it at only xxx horsepower at XXX RPMS*for 100% when that same engine is very capable of producing more power at higher RPMS.* The only thing the Lehman guys are doing is "manually de-rating" their engines by operating them well below 100%.

Or you couold say max rated RPM on a Lehman is 2200(when it is 25 or 26)*and everyon is operating them at 1800 so they are operating at 80% or whatever that comes out to be.


-- Edited by Baker at 20:43, 2008-10-10
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Old 10-10-2008, 07:54 PM   #28
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RE: Prop-pitch

John--- Question for you that may or may not be apropos to the discussion. Back in the late 1980s Kenmore Air Harbor installed new P&W PT6A-135s in their two Turbo Beavers which were built originally with old-generation PT6As of 550 shp. The PT6A-135 is rated at 750 shp. However Kenmore de-rated them to 600 shp in their Turbo Beaver re-engining project.

This same engine is used in the single-engine Otter conversion, but in that airplane it is rated at its full 750 shp.

I have never gotten around to asking Kenmore why they derated the engine for their Turbo Beaver project. Do you think it was to prolong the life of the engine or to match the structural limitations of the Turbo Beaver airframe which was originally designed and built for a 550 shp turbine? They also operate six turbine Otter conversions, and they operate the engines in these planes at their full 750 shp rating.

As to industrial diesels, what is the purpose of derating them? Is this to prolong the operating life of the engine?

Thanks,

-- Edited by Marin at 02:05, 2008-10-11
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Old 10-11-2008, 05:05 AM   #29
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RE: Prop-pitch

As to industrial diesels, what is the purpose of derating them? Is this to prolong the operating life of the engine?


ALL engines (unless killed) will have an operating life , that really is a function of how much fuel it can burn to overhaul.

Visit any eng. mfg or converters site and you will find 4 different ratings , on an industrial engine.

1 is pleasure , 300 hrs a year at full bore and only 1 hour in 12 at flank

another would be for launches and patrol boats 1000 hrs at flank a year 4 to 6 at flank in 12

There are others , ending at 24/7/365 for work boats that need this operation.

Interesting most of the different ratings are at about the same RPM, (except perhaps the pleasure 300hour) , only the loads vary.

The engines I would avoid are the ones with NO 24/7 rating at any light load.

Many of the light car takeouts like Volvo and Yannmar have onlt a pleasure rating.

The mfg /converter is RIGHT , these are poor candidated for a trawler , even tho the actual trawler use hours profile fit pleasure ratings.

No you don't have to end up with an oversized engine.

On our new design the engine will operate at flank, at the pleasure boat rating , but will operate at cruise 18K at 24/7 rating , and be really efficient at slow cruise 10-12K by the use of a ZF 2 speed tranny and CPP to actually load the engine at slower rpm.

2- EGT as failure is unacceptable . 6 cyl Fiat , sold as Ivecio marinization , tier 2 with mechanical injection.
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Old 10-12-2008, 11:03 PM   #30
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RE: Prop-pitch

Quote:
Marin wrote:

John--- Question for you that may or may not be apropos to the discussion. Back in the late 1980s Kenmore Air Harbor installed new P&W PT6A-135s in their two Turbo Beavers which were built originally with old-generation PT6As of 550 shp. The PT6A-135 is rated at 750 shp. However Kenmore de-rated them to 600 shp in their Turbo Beaver re-engining project.

This same engine is used in the single-engine Otter conversion, but in that airplane it is rated at its full 750 shp.

I have never gotten around to asking Kenmore why they derated the engine for their Turbo Beaver project. Do you think it was to prolong the life of the engine or to match the structural limitations of the Turbo Beaver airframe which was originally designed and built for a 550 shp turbine? They also operate six turbine Otter conversions, and they operate the engines in these planes at their full 750 shp rating.

As to industrial diesels, what is the purpose of derating them? Is this to prolong the operating life of the engine?

Thanks,

-- Edited by Marin at 02:05, 2008-10-11


It is all about maintenance interval. As you know, airplanes are highly regulated and when you de-rate an engine, you can affect a longer maintenace interval. That also may be the answer to FF's question in that people may buy an industrial engine under contract and swear to maitain that engine in a certain manner and then they agree to guarantee it in a certain manner. Airplane operators are sworn by law. There are so many versions of the PT6 and generally it comes down to the types of inspections you plan on doing and how often you do them. The CFM56 is the same way. Every operator wants to squeeze more flexibility out of their engines so they really are a "living" experiment. Our engines gain power and our airplanes gain take off weight all the time simply by the blessing of the FAA(and R&D and history of course).....anyway......blah blah blah.
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Old 10-13-2008, 10:34 AM   #31
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RE: Prop-pitch

As it relates to a diesel engine?
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Old 10-13-2008, 11:27 AM   #32
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RE: Prop-pitch

Eric wrote-- Did that Deere/Lugger suffer?. If not I'll throw in with ya. No glazed cylinder walls, smokin hard starting engine? Ya sure ? I'll quit ragi'n on you guys about the underloading issue.

Eric---

Last week I asked my contact at Northern Lights/Lugger how the engine in the Nordhavn 40 held up in its low-power cruise around the world. Northern Lights/Lugger was one of the sponsors of that trip (they provided the fuel) so they kept a good track of what was going on. The engine, he said, did just fine. No problems due to underloading. No smoke, no hard starting, etc. He's going down to Southern California soon and he plans to check on the current status of the boat, but in terms of the round-the-world cruise the engine experienced no problems as a result of being run at low power settings.
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Old 10-13-2008, 09:11 PM   #33
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RE: Prop-pitch

Marin, Chris and others,
Thanks for putting up with me all this time. The green light for UL dosn't extend to .. say .. a turbo Cummins like in a Nordic tug at 7 knots ?. One could use extra detergent in thier oil or/and remove or bypass thier oil cooler but what leads to cylinder glazing?. I feel very comfortable in my situation but I'm sure there are people out there that are vulnerable to this problem. There was a discussion on another site about about derating DD to cruise large yachts very slowly. Most are going slow and have never heard of under loading.

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Old 10-13-2008, 11:18 PM   #34
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RE: Prop-pitch

Eric---

This is by no means an area of knowledge for me. We're just operating our 35 year old boat the way it's apparently always been operated, and the way we were advised to operate it by our diesel shop and friends in the marine diesel industry. From what I gather from the folks with older GBs on the Grand Banks owner site, pretty much everyone with the kind of engines we have operates them within the same power range--- 1500 to 1800 rpm. Many of these boats are woodies even older than ours and have their original engines. This may be underloading the engines, but these particular engines seen to run forever when operated in this power range. I would not suggest, however, that what works for a 1950s design Ford Lehman 120 will work for some other type of engine.

Nordic Tug markets their boats as being able to cruise economically at seven or eight knots but cruise fast when necessary at twelve or fourteen or whatever knots. Hence their term "fast trawler." We have friends with a brand new Nordic Tug, albeit with a Volvo diesel as they don't use the Cummins in this model (34') anymore. But so far as I know they cruise it at a very economical 8 knots or thereabouts and have not been warned by the factory not to do this. Now it may be that they are supposed to run it harder for x-amount of time periodically. I'll try to remember to ask them next time I see them.

Also, I neglected to mention that my friend at Northern Lights/Lugger told me the engine in the Nordhavn 40 that did the world cruise had been properly broken in prior to embarking on their long, low-power cruise. I don't know if that makes any difference but it may be a factor.

-- Edited by Marin at 00:20, 2008-10-14
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Old 10-14-2008, 04:26 AM   #35
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RE: Prop-pitch

" but what leads to cylinder glazing?."

The cylinder seals by the combustion gases getting behind the piston rings and forcing then against the cylinder wall to create the seal.

With very low loads the pressure is too low , so blowby and burnished (lightly polished) cylinder walls result, instead of a good seal.

The burnishing will smooth out the honed condition of the cylinder walls , so the engine will wear faster and burn oil more rapidly.

With square cut rings the seal is better at low loads than the more modern trapizoidal.

The Deere that went round may be suffering this problem , no one has disassembeled it to find out.

Also IF the unit has electric injection the computer does change the timing and squirt size to load the engine (advance the timing) to work a bit harder.
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Old 10-14-2008, 09:29 AM   #36
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RE: Prop-pitch

For the Detroit Diesels the 'rating' is changed by the size of the injectors. An 8v92 could be 400 hp or it could be 425 or 350 by the amount of fuel squirted in each time. Different injectors are available depending on how much power you want to produce.

NASCAR uses restrictor plates to limit the amount of air that the gasoline engine can get. I would bet that the airplanes have a similar device if they are derating an engine. Remember that gasoline engines regulate speed by regulating air, diesels by regulating fuel.

The number of and size of explosions in an engine determine it's longevity. While designed to withstand such explosions there is a limit to how many it can stand before it wears out. Take a tennis shoe and drag it across the asphalt. Some wear, but not much. Now put a bowling ball on it and do the same drag. More wear? Bigger explosion in the engine means more pressure on the top of the connecting rod bearings, wrist pin, piston, rings are expanded against the cylinder wall more forcefully, etc.

Modern electronic control engines make things much easier. Fuel can be regulated, timing can be adjusted, lifter openings changed, all by the computer. This is why there is an aftermarket for hop-up chips for your diesel pickup, or your Monte Carlo. You can change the parameters to get more or less of something, usually at some cost somewhere.

30 years ago we put dual quads on our V8's to make them faster. Dual quads allowed us to get more air into the engine and dump way more fuel than the engine actually needed. Mom's car might have the same engine with a 2 barrel carb. She wasn't as fast. She also didn't have to have a valve job as often. Her engine didn't get as much blowby in her crankcase either. So, her oil stayed cleaner longer because the explosion in each cylinder was smaller. Her maintenance schedule reflected the way she drove. My maintenance schedule was dependant on how much money I had. If all things were equal though, I would have changed oil much more often than Mom because I polluted my oil faster.

Ken
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Old 10-14-2008, 12:02 PM   #37
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RE: Prop-pitch

Quote:
Vinny wrote:
Just changing*the time or interval for*valve adjustments, oil change, filter change etc... and then*stating that the engine is now rated at 250hp*@ 3,400 with a TBO of 2,500 hrs*instead of 285 hp @ 3600 with a TBO of 2,000 hrs doesn't make it so.* Something in the engine has to change to slow that puppy down, like valve timing, valve overlap, exhaust restriction something.
I believe in the case of the PT6A-135 turbine I was talking about earlier, the only things that were changed to derate this 750 shp engine to 600 shp were the power settings used, N1, N2, etc.* (I think that's the correct term for the shaft rpms in a turbine--- I haven't flown one for a long time).
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Old 10-14-2008, 05:18 PM   #38
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RE: Prop-pitch

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Vinny wrote: Marin

So then in affect the change in*the power settings is like*putting a governor in place thus chopping 150shp.* Now the maintenance schedule can be changed due to the lower RPM's.

I guess.* The derated version of the engine may use a different prop than the fully rated version as well.
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Old 10-14-2008, 07:26 PM   #39
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RE: Prop-pitch

Yep, I think we're all on the same page, just saying the same thing different ways.
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Old 10-14-2008, 09:11 PM   #40
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RE: Prop-pitch

Ken, I,m not on the over loading over proping page .. not at all. If you have a Ford engine of 120 hp at 2500 rpm and you over prop it 200 rpm at 2300 your'e obviously very over proped at 2300. But going down the engine speed scale where are you NOT overloaded. You don't know. Nobody knows. At what rpm can you operate continiously and get the maximum power out of your engine? You don't know. Maybe 2000 but I would'nt feel comfortable running that engine at 22 or 2100 rpm. The engine would have a max power of about 85 hp .. maby 90 .. but maybe only 80. If you know you'll only need 80 hp then the correct place to be is with a 90 hp engine, then you can prop the engine correctly, as Marin stated long ago on this thread, and operate the engine at the correct load and engine speed. On a full displacement hull over proping works much much better as the boat resistance drops very fast as one,s speed falls below hull speed. This means that if you slow down even one knot the power required is so much less that the engine experiences a large drop in load that can be overcome by over proping but again one looses the ability to run the engine near max power. If one only needs 60 % of the power in thier boat and they can't afford to repower with lower power engines, then over proping becomes a possible half assed solution. Am I on the same page with you Ken ? I guess so since I've said if your'e willing to suffer the consequences and/or the side effects one can do anything one wants.

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