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Old 01-04-2011, 08:57 PM   #1
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Horsepower versus Displacement

There have been a couple of threads that have discussed HP and how much a particular boat needs. Was looking on Yacht World for how large a boat I could find with a Lehman 120.

Saw a 50' Marine Trader last winter with a single Lehman 120.

LOA 50'
Beam 15' 5"
Draft 4' 8"
Displacement 46,000


This one certainly has to be one of the biggest with a single 6 cylinder diesel.

LOA 56'
Beam 16'
Draft 7'
Displacement 140,000

Engine* DD* 6-71* 170 HP!*

http://www.yachtworld.com/core/listi..._id=51769&url=


Ted
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Old 01-05-2011, 07:01 AM   #2
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RE: Horsepower versus Displacement

Quote:
O C Diver wrote:

There have been a couple of threads that have discussed HP and how much a particular boat needs. Was looking on Yacht World for how large a boat I could find with a Lehman 120.

Saw a 50' Marine Trader last winter with a single Lehman 120.

LOA 50'
Beam 15' 5"
Draft 4' 8"
Displacement 46,000


This one certainly has to be one of the biggest with a single 6 cylinder diesel.

LOA 56'
Beam 16'
Draft 7'
Displacement 140,000

Engine* DD* 6-71* 170 HP!*

http://www.yachtworld.com/core/listi..._id=51769&url=


Ted
Here is another

http://www.yachtworld.com/boats/2011.../United-States

*
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Old 01-05-2011, 08:19 AM   #3
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RE: Horsepower versus Displacement

http://www.pacificboatbrokers.com/de..._Number=NW3266
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Old 01-05-2011, 08:19 AM   #4
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Horsepower versus Displacement

Roughly it takes 2 hp per ton (2240lbs of displacement) to move at cruise,

3 Hp per ton is about all most folks will be willing to pay for that purchase trawlers.

5 Hp per ton is about all a displacement boat can handle without making huge waves.

The "doccument " USCG tonnes is VOLUME , not weight, don't be fooled.


Displacement 140,000 Engine* DD* 6-71* 170 HP!

so 140,000 divided by 2240 is 62,6x2 is 125 HP or x 3 is 187hp.

AS DD are properly rated if you can achieve rated RPM ,* cruising at LRC should be quiet (I'd guess 1500@ SL x 1.15 for the 125 HP)* at say 7 to 7.5 K

Fuel burn , guesstimate* 125HP divided by 16 is 7.8 or about 1 mpg.





-- Edited by FF on Wednesday 5th of January 2011 09:27:54 AM
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Old 01-05-2011, 02:31 PM   #5
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RE: Horsepower versus Displacement

Our Roughwater trawler is 80,000+ lbs with a single DD 671, 170 hp that can cruise between 7 and 10 knots with a max of 12 knots.* At 10 to 12 knots we are pushing a lot of water and the bow wave is quite big.*


*
80,000/2240=35.7 X 2 =71.4 hp** **35.7 X 5 = 187.5 hp.* Hull speed is 7.2 to 9.4 knts.
*
Many of the older commercial fishing trawler are/where powered with DD 671s.* Some have repowered as 170 hp was not big enough when dragging all fishing gear. *****
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Old 01-05-2011, 09:24 PM   #6
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RE: Horsepower versus Displacement

Radiant Star (mentioned on the forum several times before) has 240hp and a disp of 90 tons. That gives her 2.66 hp per ton. She came to Anacortes Wa on her own bottom from Scotland so it would seem she had sufficient power. As a fishing boat in the North Sea she probably operated considerably below that w a full load of fish. I looked at a 36' Fisher that has less than 4hp per ton and my own Willy has 5hp per ton. Eight ton boat over powered w 40hp. That's hard to process.
O C,
If you have a 50' 70 ton boat w a 120 Lehman (2.4hp per ton) you're not going to be slog'in along at 1600rpm. You'll be at 2100/2200 rpm burning 4.5 to 5 gph. And you'll burn more fuel if you have a 500hp engine slog'in along.
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Old 01-06-2011, 04:23 AM   #7
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RE: Horsepower versus Displacement

5gph for a Lehman will have reduced service life,

it is not a HD engine and most are happier at 3 gph and under .
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Old 01-06-2011, 10:39 AM   #8
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RE: Horsepower versus Displacement

Well.........You have a lot of company w that opinion but I think you'd all be surprised to find out they can probably work hard like most any other diesel.
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Old 01-06-2011, 10:41 AM   #9
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RE: Horsepower versus Displacement

We cruise at 1200 to 1500 rpm with a 3 to 1 rations, turning a 38 dia. 28 pitch prop and get 2+ mpg.* Many of the older commercial tugs turned about 500 to 1000 rpm turning huge props, 6 to 10 ft in dia.* My diver was used to working on small pleasure props so when he dove on the Eagle he was impressed until he dove on the 70 ft tug next to us was a 6 to 8 ft prop.* Turn a small prop at high rpm or turn a large prop at low rpm.* *So it depends on the hull, engine and running gear. ****

*
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Old 01-06-2011, 10:54 AM   #10
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RE: Horsepower versus Displacement

"5gph for a Lehman will have reduced service life,"

Can a 120 Lehman even burn that much?
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Old 01-06-2011, 11:11 AM   #11
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RE: Horsepower versus Displacement

I had a book on a 120 Sabre (same Ford 380 cu in engine) and it says 6 GPH WOT propped for 2500 rpm.
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Old 01-06-2011, 12:05 PM   #12
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RE: Horsepower versus Displacement

Quote:
nomadwilly wrote:

I had a book on a 120 Sabre (same Ford 380 cu in engine) and it says 6 GPH WOT propped for 2500 rpm.
Here is a link to an online manual:

http://bf494.co.uk/assets/Ford_Lehman.pdf

They Claim 114 continuos BHP at 2500 RPM. Assuming no more than 16 HP per gallon, that would be 7+ GPH WOT.

Ted

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Old 01-06-2011, 12:19 PM   #13
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RE: Horsepower versus Displacement

Quote:
nomadwilly wrote:

Well.........You have a lot of company w that opinion but I think you'd all be surprised to find out they can probably work hard like most any other diesel.
No, they apparently can not.* The base engine that was marinized to make the FL120 (and other marine variants) was designed in the 1950s to be a "heavy" truck engine for Ford trucks both in Europe and in the US.* For that purpose it proved to be a dismal failure.* The engine did not hold up at all under the higher loads, higher rpms, and constantly changing loads and rpm that you have with over-the-road use.*

I had read about this a number of years ago but a couple of years ago I got to talking to a fellow in Ganges who until his retirement had owned a large engine overhaul facility in England.* He asked me what kind of engines we have in our boat and when I said FL120s he said he'd worked on hundreds if not thousands of those engines over the years (the stock Ford of England Dorset base engine, not the Lehman marinized version).

He confirmed their total unsuitability for being operated at high loads and high rpms but went on to say that they proved to be excellent in industrial and agricultural applications like cranes, generators, big pumps, combines, etc. where the loads are relatively low and the power requirement is relatively constant.* (Which I had read earlier as well.)

I asked him why the engine proved to be so bad for heavier work like the trucks it was designed for and he said that when operated hard, particularly when operated hard at higher rpms, the moving components simply don't hold up.* He said the crank bearings and rod bearings are vulnerable to high wear under high loads.* The engine overheats very easily under high loads.* He said the number one killer of that engine is too much heat.* The head gasket, he said, is a major weak point.* Any overheat at all and it will go, and then the head will warp almost immediately.* He said most of the Ford Dorset engines he and his shop had overhauled had failed because of overheating, particularly in the early days when they were being installed in trucks.

He also said the CAV/Minnimec/Simms in-line injection pump is a very high wear item if the engine is operated at higher rpms.* His shop was constantly replacing and rebuilding them--- in his opinion the pump is a fundamentally poor design and was not built all that well.* Along with overheating, he said the injection pump greatly contributed to the engine's failure as a truck engine.

He gave me some advice on running our FL120s that was in line from what I had been told by friends in the marine engine industry.* He said that if we ran our engines in the band between 1500 and 1800 rpm they would last "forever."* He said to never run them too cool-- they need to be at their proper operating temperature to maximize service life.* The proper temperature range is from 180 to 190 degrees (coolant temperature).* And he said to NEVER let them overheat.* Even a little bit.* He said if the temperature ever starts climbing above 190 degrees shut it down immediately.

So.... good, reliable, high TBO engines but only if operated in a relatively narrow rpm band at conservative loads.* Push them too hard and they will begin to have all the problems that caused them to be dropped from highway use within a few years of their introduction.

*
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Old 01-06-2011, 02:32 PM   #14
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RE: Horsepower versus Displacement

Eric is right on, the Lehman as well as the DD two strokes, older design Perkins, Cats*etc had their day, many many days ago. That does not mean*that the Lehmans can't keep on going, it just takes TLC and not running them on the pins for hours on end. Last summer I talked and cruised with several Lehman owners who echo the same as Eric.

As with gas engines, light and heavy diesels have come a long way in the past 30 years. More sophisticated electronics are part of the equation, not always for the*better either in marine adaption when meeting Tier 11/111 requirements
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Old 01-06-2011, 02:53 PM   #15
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RE: Horsepower versus Displacement

Well it looks like the Sabre people disagree w your guy Marin. 114hp at 2500rpm is WAT above 90% load. Why would they say their engine can do that if it could'nt. And why would Lehman, in their search for a base engine choose an engine that can't take heavy continuous loads. That's what marine engines do,except old men driving trawlers that can't afford 4gph or have a boat overpowered by the non-professional manufacturer. I can't read the manual very well but it looks like their endorsing very heavy continuous loads.
By the way Marin (since I'm pick'in on you (and you can take it)) there's no such thing as revolutions per minuites. One minuite of time or it makes no sense. Nit pick of the day.
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Old 01-06-2011, 07:16 PM   #16
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RE: Horsepower versus Displacement

Quote:
nomadwilly wrote:

1.* Well it looks like the Sabre people disagree w your guy Marin. 114hp at 2500rpm is WAT above 90% load. Why would they say their engine can do that if it could'nt....

2.* By the way Marin (since I'm pick'in on you (and you can take it)) there's no such thing as revolutions per minuites. One minuite of time or it makes no sense. Nit pick of the day.
1.* Nobody's saying the engine can't do it, just that it can't do it very long.* A 1950s engine is a 1950s engine.** To think it can deliver the same longevity under hard use as a newer generation engine*is not a smart assumption except in the eyes of your diesel shop, which will love you for it.* The diesel shop we use has seen a lot of failed Lehmans over the years, and they told me not long after we bought our boat that in almost all cases the root cause of the failure was running them too hard, too fast, and too hot for too long.* Failed head gaskets were the most common specific cause of the failure they said.

Lehman created the FL120 in the mid-1960s.* At that time there were not a lot of engines on the market that would lend itself to this kind of conversion so their choices were limited.* Also, people viewed engine operation in the '60s considerably differently than they may do today.* Cruise rpm ranges for these engines were conservative.* Our owners manual itself does not call out any specific cruise power--- it simply says (verbatim)*"Cruising rpm varies with the conditions and type of engine fitted.* Please check with your dealer for his recommendations."* Our manual includes a separate page from the GB dealer who sold the boat new in 1973.* The page contains a list of operating and maintenance recommendations and intervals.* Under "recommended cruise power" it says 1600 to 1800 rpm.*


2.* You're right but....* I see "rpms" used in print*to mean a range of rpm.* What's plural is not the word*"minute" but the whole acronym.* So it means "more than one specific rpm."* But.... just because I see the term "rpms' used by various motoring journalists doesn't mean it's correct.* It may just mean that we're all wrong
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Old 01-06-2011, 09:54 PM   #17
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RE: Horsepower versus Displacement

" Nobody's saying the engine can't do it "
I've have said the engine probably can do it.
As you know I despise your attitude that if it wasn't made yesterday it can't possibly be any good. A continuous rating is proof that the engine is rated to do what is speced to do. Does it not say it's rated to do 114hp at 2500rpm continuously?
"The diesel shop we use has seen a lot of failed Lehmans over the years"
Indeed. I've seen 7 of them lined up in a row at Doc Freeman's.
"Also, people viewed engine operation in the '60s considerably differently than they may do today." How did you know how people ran marine engines in the 60s ? They were'nt as concerned w fuel consumption as we are today and in the 60s the only diesel engines found in any numbers was the 6-71 and some of it's relatives and they were only found on 50 footers and other large boats. Diesel engines were too heavy, stinky and expensive for yachts. And the commercial boats as I recall were run hard.
"Cruise rpm ranges for these engines were conservative." I think you're just mak'in that up. How could you know what the habbits of diesel marine engine operators were in the 60s???
" Under "recommended cruise power" it says 1600 to 1800 rpm. "
American Marine is a boat manufacturer not an engine manufacturer. And in my opinion AM (GB) has made some irresponsible decisions regarding other things so why not dictate other bad stuff.
Even if I am correct in that they DID recomend running the engines at 114hp at 2500rpm I certianly would'nt do that. But I would run one at 2100 if 2500rpm is attainable at WOT.
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Old 01-06-2011, 10:12 PM   #18
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RE: Horsepower versus Displacement

While I don't mean to get in between the Nomadwilly/Marin discussion, I*would suggest that*more modern engines are probably really no different than the FL, if you run them hard near their upper load design limits, you will experience reliability/longevity issues.*
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Old 01-06-2011, 11:15 PM   #19
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Horsepower versus Displacement

Quote:
Eric---- This will come across as one of those overly defensive responses I've been accused of making from time to time, so keep in mind that you asked.......




nomadwilly wrote:

1.* I've have said the engine probably can do it.

2.* As you know I despise your attitude that if it wasn't made yesterday it can't possibly be any good.

*3.* A continuous rating is proof that the engine is rated to do what is speced to do. Does it not say it's rated to do 114hp at 2500rpm continuously?

*4. How did you know how people ran marine engines in the 60s?

5.* in the 60s the only diesel engines found in any numbers was the 6-71 and some of it's relatives and they were only found on 50 footers and other large boats. Diesel engines were too heavy, stinky and expensive for yachts.

6.* "Cruise rpm ranges for these engines were conservative." I think you're just mak'in that up. How could you know what the habbits of diesel marine engine operators were in the 60s???

*7.* But I would run one at 2100 if 2500rpm is attainable at WOT.
1.* You're wrong in this case. Ford said it was a crappy engine and*it was*their engine.* It's why they yanked it from their engine lineup for trucks just a few years after its introduction.* The engine was on the chopping block for discontinuation when somebody thought to try it as a stationary engine running a generator.* It managed to do this without self-destructing as it had in the trucks and since Ford of*England*had a lot invested in it they decided to see if they could*market it as an industrial engine.* For this low-load, low-speed purpose it proved quite good.

2.* If everyone thought like you we'd all still be flying around in*rotary-engine biplanes and using scythes to cut the lawn.* Strictly in my opinion, yesterday's*stuff has historical and sentimental value.* Other than that, it's pretty worthless if you want*to use it for anything important, particularly something of a commercial nature.** Some people prefer to cling to the past.* I'm not one of those people.

Some people say new stuff is too complicated, too unreliable, and it will never be as good as the*old stuff.* Used to be if you bought a car you had to have a guy walk in front of you with a flag to warn people you were coming.* Cars were considered newfangled, complicated, unreliable, and downright dangerous.* How'd that work out?* (Our new Range Rover didn't come*with a flag guy.**Did the dealer rip us off?)

I have no patience or use for old stuff unless I can't afford to replace it with new stuff, which is often the case.* So I'll use the old engine or car or boat or plane or computer or whatever, and I'll treat it right and operated it properly because I need it to work for me, but that doesn't change the fact that*it's old and I'd love to be able to toss it in the dumpster and replace it something brand new.* I've quoted in the past*the famous Boeing engineer, Ed Wells (the "father of the B-17"), who in the early*1950s when asked about the risk of switching from piston to turbine engines*answered, "Life's too short to waste it*working on propellers."* That sums up perfectly my feeling about all old technology.

3.* Yes, but that doesn't mean it will have a long life if operated this way.* "Continuously" is a relative term.* All it really means is that the engine will operate continuously at this power rating until it fails.* It's like a lifetime guarantee on a part.* The part is guaranteed for the life of the part, not your life, your boat's life, your car's life, etc.* It's actually a pretty meaningless guarantee if you think about it.* Ford didn't say, "This engine [the Dorset]*will operate continuously at this power rating for 1000 hours or 3000 hours or 10000 hours."* They simply said it would operate continuously at this power setting for some indeterminate amount of time without a catastrophic failure.* As it turned out in the trucks it was designed for, the indeterminate amount of time was pretty damn short.

Engines come with warranties. Or the engine is included in the overall vehicle, boat, etc. warranty.* My Ford F-250 with the*"bulletproof"*300 cubic inch six in it had a 50,000 mile or three year, whichever came first, warranty on it.* That's not very long.* And at 52,000 miles the engine split its number three cylinder wide open while idling at a stoplight.* Bad block casting the repair shop determined.* Ford said, sorry, the warranty was up at 50,000 miles so it's not our problem.

So how do you define how much time "continuous" represents?

4.* I've talked to people who had or ran*boats in those days.* Including the captain/manager of a 120' corporate yacht who has probably*had more boating experience with both recreational and commercial vessels*than everyone on this forum combined.* We bought our GB while I was actively working with this fellow and he gave me the benefit of his experience using these types of engines in the late 60s and early 70s.

5.* Grand Banks boats*have always been diesel powered since their introduction in the early 60s.* So were Alaskans.

6.* Again, from talking to them.* And I'm not talking just boats here.**We had family friends who had 16,000 acres of wheat and oil in Nebraska in the 60s when I was in college at Colorado State.* I spent some school breaks with them and the husband spent a lot of time talking engines and combines and tractors and whatnot with me because I was interested in that stuff.**He was all about maximizing the service life of his equipment because it had a direct impact on his bottom line.* And because of my mother's job in Hawaii, I got to know several commercial tuna fishermen in the '60s.* Same deal-- I was a kid interested in boats and engines so they told me about them--- most of their aku*boats had 6-71s in them.

7. Your diesel shop would love you if you did that for a few years because it would mean they could all keep making their Porsche payments


-- Edited by Marin on Friday 7th of January 2011 01:32:33 AM
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Old 01-07-2011, 03:27 AM   #20
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RE: Horsepower versus Displacement

A visit to any engine mfg site will show at least 4 power ratings.

IF there is only one , its not suitable as a boat engine , for long at its HP rating.

AS we get into flyweight engines , car transplants Yannmar , VW, BMW , Toyota the problem grows.

AS many tiny engines are turboed to huge advertising HP numbers the difference between add hp and 24/7 hp grows.
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