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Old 08-30-2010, 08:02 PM   #1
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Lehman 80-HP

Turns out the little 31-foot Lien Hwa Sea Horse trawler that I thought was powered by a six-cylinder, 120-hp Lehman is powered a four-cylinder, 80-hp Lehman (my mistake).* I* gather these were very popular in*twin-screw Taiwan trawlers like the CHB34 and as auxiliaries for larger sailboats or motosailers

I have a few questions for the Forum.* First, what ought to be the fuel consumption of this engine?* Second, as long as I don't run her too hard--and am happy with running at seven knots or so--is there any reason this would not be a good powerplant for this trawler?* And finally, is replacing this engine with a 120-hp Lehman an incredibly complicated process?* I wonder about motor-mount location issues and such.

Thanks in advance for your replies.
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Old 08-30-2010, 09:00 PM   #2
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Lehman 80-HP

The 80hp (or 90hp depending on which manual you read) is essentially the 120 hp engine with two cylinders lopped off. Obviously it's not that simple but that's what it is. The FL120 operators and parts manuals actually cover three engines--- the 4 cyl NA, the 6 cyl NA and the 6 cyl turbocharged.

I've not heard or read much about the 4 cylinder version. American Marine (Grand Banks) never used them so far as I know except in a very small number of twin engine GB32s which were built with two of these engines each. And there may have been a few GB32s that got one of these engines instead of an FL120 but I'm not sure if my memory is correct on this or not.

In terms of power for a 31 foot boat I would think it would be more than sufficient. Repowering with an FL120 would probably be more trouble than it's worth. And there are much better, lighter, more efficient engines around to repower with anyway if you really want to do that.

You might want to call American Diesel (Bob and Brian Smith) for an opinon on swapping out a four cylinder Lehman for a six. They could tell you what's invovled, but I suspect it's more than is worth putting into the boat in question. Since you're going to be redesigning and fabricating the engine mounts anyway, it would seem to make more sense to re-power with a modern powerplant in the same physical size range of what's there now.

-- Edited by Marin on Monday 30th of August 2010 09:03:11 PM
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Old 08-31-2010, 04:11 AM   #3
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Lehman 80-HP

31-foot First,

as long as I don't run her too hard--and am happy with running at seven knots or so-

what ought to be the fuel consumption of this engine?

With perhaps 28 ft lwl it will be far easier to run 6K or even 6.5 (maybe) than 7K

While the boat may actually go 7K it will take probably double the fuel as 6K.

Measure the LWL and take the sq root of it.

Multiply that number by .9 for LRC long range cruise or by 1.15 for economical (fuel stops easier) coastal cruising.

With no wind LRC fuel burn should be just above 1 gallon per hour Coastal closer to 1 .75 .

Just a guess but 7.5K would be full throttle , 4.5 gph, NOT RECOMENDED for more than a 5 min speed trial.

If you want to go faster use statute miles , the numbers will seem bigger.

OR get a boat with double the LWL , for a 8K cruiser.



-- Edited by FF on Tuesday 31st of August 2010 04:13:31 AM
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Old 08-31-2010, 08:56 AM   #4
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RE: Lehman 80-HP

I have one in a 35 foot ex-fishing boat. *It had a 160 hp Isuzu truck engine in it when I got the boat and I swapped it out for a 30 year old 80hp Ford that came out of a 45 foot sailboat for a re-power. *It runs fine and average speed is 6-6.5 knots and I estimate around 4-5 litres per hour consumption. *I have a 3:1 gear box so can swing a fairly big prop. *Both the engine and gearbox were freebies but still have lots more life left in them.

I tend to agree with Marin that if you wanted to re-power for more HP then a modern 4 cylinder of similar or smaller physical size would be an easier fit and still give some more power. * Marin is also right about the similarity with the 6 cylinder Ford, so reliability is the same so no gain in that regard by changing to the bigger engine.
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Old 08-31-2010, 05:14 PM   #5
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RE: Lehman 80-HP

Chris:
For what its worth, I have a Perkins 4-236 (4 cylinder, 236 cu. in, 60 HP) and it does just fine. I burn a little more than 1 gph at 1600 rpm. Boat weighs 24,000 lbs. with fuel and water. Your 80 hp ought to work just as well.
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Old 08-31-2010, 11:05 PM   #6
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RE: Lehman 80-HP

Chris,
I've actually owned both engines. The 90 is a 4 cylinder version of the 120. The 90 I had in an Albin 27 Sport Cruiser. The Albin toppped out at a little over 14 knots and would cruise all day at 13 knots. I don't remember what rpm I ran her but it was probably fairly high. The 90 is a nice little engine but like the 120 loud as hell.
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Old 09-03-2010, 04:01 AM   #7
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RE: Lehman 80-HP

Quote:
Gulf Comanche wrote:

Chris:
For what its worth, I have a Perkins 4-236 (4 cylinder, 236 cu. in, 60 HP) and it does just fine. I burn a little more than 1 gph at 1600 rpm. Boat weighs 24,000 lbs. with fuel and water. Your 80 hp ought to work just as well.
Mike
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You sure about that? *I thought the 4236 was an 85hp engine and the 4154 was 60 and the 4108 was 50? *I had the 4236 in my Prairie....great little engine!!!
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Old 09-03-2010, 10:50 AM   #8
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RE: Lehman 80-HP

Chris,Another opinion:
Keep the 80hp. Load the engine properly with the propeller that allows 2500rpm at WOT.
Load the engine while cruising such that you burn AT LEAST 2 gph, That will be a 50% engine load. Then just keep your tanks clean and cruise.
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Old 09-03-2010, 01:24 PM   #9
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RE: Lehman 80-HP

John:
60hp was how the PO (original owner) advertised and sold the boat to me. He had the boat custom built so I assumed 60hp is correct. I have read that the 4236 is 85hp, so that has always kind of bugged me.
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Old 09-04-2010, 04:02 AM   #10
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RE: Lehman 80-HP

"60hp is correct. I have read that the 4236 is 85hp, "

There probably both "right".

Go to any site from an engine mfg , and you will find at least 4 hp ratings.

All the way from the "pull the boat out of the hole in to a plane rating" ( usually 30 seconds) to the 24/7/360 rating.

The differences will frequently be 50% or more.

For a displacement boat the 24/7 ratings should be the key , and remember you want to USE 70- 80% or so of the 24/7 during LRC (long range cruise) 90% is fine for coasters where fuel access is no concern..
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