Horsepower versus Displacement

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O C Diver

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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/listing/boatMergedDetails.jsp?boat_id=2200072&ybw=&units=Feet&currency=USD&access=Public&listing_id=51769&url=


Ted
 
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/listing/boatMergedDetails.jsp?boat_id=2200072&ybw=&units=Feet&currency=USD&access=Public&listing_id=51769&url=


Ted
Here is another

http://www.yachtworld.com/boats/2011/Jet-Tern-Marine-Selene-Ocean-Trawler-1668264/Seattle/WA/United-States

*
 
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
 
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. *****
 
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.
 
5gph for a Lehman will have reduced service life,

it is not a HD engine and most are happier at 3 gph and under .
 
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.
 
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. ****

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

Can a 120 Lehman even burn that much?
 
I had a book on a 120 Sabre (same Ford 380 cu in engine) and it says 6 GPH WOT propped for 2500 rpm.
 
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

*
 
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.

*
 
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
 
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.
bleh.gif
 
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.
bleh.gif
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
smile.gif
 
" 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.
 
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.*
 
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.......
smile.gif





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
smile.gif



-- Edited by Marin on Friday 7th of January 2011 01:32:33 AM
 
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.
 
Marin,About #1 YOU are wrong. "Iv'e said the engine probably can do it" I did say that.
Anyway if I repeat you'll repeat and that serves no purpose that is positive.
But I do need to make an adjustment to my position in that you are partially correct on several issues. My Mitsu is rated for 1 hr WOT but I wouldn't do that. I saw a Mitsu on Yacht World that had over 10000hrs on it and it didn't get there at WOT. But it could have at 80% load. Diesel engines in industry do it every day. If your Lehman engines are actually weak and can't haul the mail so be it and I'm glad I hav'nt got one. I looked at perhaps over 100 boats powered by Lehman's and I don't recall any repowers. And I don't think for a minute they were ALL baby'd. Most of the engines had 4 to 6000hrs TT or since MOH. Like most anything there's a sweet spot that works best. Engine rpm and load sweet spots are almost always a point of minimal vibration. Has nothing to do w what's good for the engine or where the most torque is developed or where the lowest fuel burn is experienced. I would run my Mitsu at 2500rpm most of the time if I felt like it and that is equivalent to 2100 on the Lehman. Maybe it would'nt last 15000hrs but it would probably last 10000hrs and there's basically no chance that's going to happen.
Ha Ha * * ...I just thought of somth'in * *... I repowered my Willy that had a perfectly good 4-107 Perkins so maybe you're right * * new things are good!
 
nomadwilly wrote:

Marin,
1.* If your Lehman engines are actually weak and can't haul the mail so be it and I'm glad I hav'nt got one.

2.* Ha Ha * * ...I just thought of somth'in * *... I repowered my Willy that had a perfectly good 4-107 Perkins so maybe you're right * * new things are good!

*
1. The Ford Dorset (base engine for the FL120) is indeed a weak engine when operated in the manner it was originally intended to be operated, as a "heavy" truck engine.* In that sort of service, pulling heavy loads up hills, keeping up with the increasing highway speeds of the late 1950s, etc. it could not "haul the mail."

However, as Ford discovered, the same engine did very well in stationary industrial service and then as a powerplant in relatively low-power, low-load applications like combines, farm tractors, and so on.* So in boat service, if operated conservatively (as opposed to the way Ford had hoped the engine would perform) it is a long-lived, reliable engine as thousands of boats have proven over several decades.

Based on the history of the engine I have read and what I have been told about the engine by people who dealt with them for decades in the US and the UK, you can't get in trouble with a Dorset (FL120) unless you operate it in the manner in which it was operated in Ford's trucks--- high loads, high rpm.* That's when the engine will eventually bite you and enrichen the mechanics at your diesel shop.

2.* A popular repower for Grand Banks that were built with the FL120 or FL135 is the 150hp N/A Lugger (I don't know the* model number).* The Lugger is very close in size to the Ford engine but is based on a modern diesel (John Deere I think) with high reliability, good efficiency, and enough power to let the boater run the GB's semi-planing hull at a faster speed without stressing the engine.* Should we ever decide to spend the money to re-power our boat, this is the engine we would use if it was still available.


-- Edited by Marin on Friday 7th of January 2011 12:32:56 PM
 
DavidM wrote:

New can be better, but not necessarily for low speed trawler use. I'll give you an example.

The newish Yanmar 4JH4 HTE is a 2 liter turbocharged 110 hp engine. You might think that it would be a good engine to push a 20,000 lbs trawler to hull speed producing 60 hp. Maybe but it would be producing 30 hp per liter to do that. And you have the extra complexity of a turbo and intercooler.

Then look at the John Deere 4045D a newish 4.5 liter naturally aspirated engine. It has an M2 commercial rating. It would be a good choice for that 20,000 lb trawler as the 60 hp would only be 13 hp per liter.

Big iron beats sophisticated turbo charged in all respects for a displacement speed trawler in my book. Unfortunately there are really no new 6 liter and up normally aspirated engines. So if you want a new 30,000 lb trawler it will come with a turbocharged engine.

David
I was thinking more like 20,000 pounds would require 30HP and 30,000 lbs. would require 45 HP. Think you have several non turbo sub 2700 rpm choices that can produce 30 to 45 HP all day.

Ted

*
 
Marin,
They made the Lehman conversions for many years. If it was known (how could it not be) that they were weak then why did'nt Lehman get another engine to marineize?Luggers popular in GBs? Never seen one listed or otherwise. I saw one GB that had a Deere in it but you said that was original. If that GB36 w the 55 Yanmars was FG and on the west coast I'd have been on it * * ..prolly.
 
nomadwilly wrote:
1. They made the Lehman conversions for many years. If it was known (how could it not be) that they were weak then why did'nt Lehman get another engine to marineize?
2. Luggers popular in GBs? Never seen one listed or otherwise.
1.* They did.* It's called the FL135.* Also, by the time Lehman got around to marinizing the Ford Dorset into the FL120 it had been in industrial and agricultural service long enough to have built a good reputation in this service.* It was only used in trucks for a few years.* And as you said earlier, there weren't that many diesels around in the 60s that lent themselves to marininzations for smaller boats.******

2. Perhaps the people who own them don't want to sell them.* Who knows?* But Alaska Diesel-Electric aka Northern Lights/Lugger told us they have re-engined quite a few GBs, not just in this area but all over.* Woodies and glass boats both.* I don't know exactly how many "quite a few" is.* This came out in a discussion we had with them not long after we bought our own GB and were exploring the options to get rid of the two FL120s.

There are several people on the GB owners forum who have GBs that were re-engined with Luggers.* From the accounts I recall reading, it's an excellent conversion for a GB32 or GB36.* For what most GB buyers want today the 150 hp Lugger is too small for the GB42 although if one didn't want to go much faster than 9 or 10 knots a pair of them would work great.* The FL120 was the standard powerplant for the GB42 until they moved up to FL135s and then larger engines like Cats and whatnot.




-- Edited by Marin on Friday 7th of January 2011 02:31:56 PM
 
I notice the wood GBs are going for cheap. Seems strange people would invest large amounts of money in a boat that won't deliver at sale time. But that guy w the little Yanmars sold his. What would 2 new luggers installed cost?
" They did.* It's called the FL135." That's the same 380 cu in Ford as the 120 isn't It?
Also you don't see many 135s so they let a lot of lemons out the door before doing anything about the "problem".
Anything w a Lugger would be nice but in a yacht any other engine would do just as fine. I could have put a 40hp Lugger in Willy but as soon as I got a wiff of the price I was outta there. It was ridiculous! I do recall MER was advertising a near slip-in Deere for a Lehman replacement but I've not seen one of them either. I have seen a lot of Lehman rebuilds though. You say that's usually over heating? I wonder how many over heated Lehman's got that way from bad design or operator negligence. I'd vote on the latter.
 
nomadwilly wrote:

1.* I notice the wood GBs are going for cheap.

2. What would 2 new luggers installed cost?

3. " They did.* It's called the FL135." That's the same 380 cu in Ford as the 120 isn't It?* Also you don't see many 135s so they let a lot of lemons out the door before doing anything about the "problem".

4. I wonder how many over heated Lehman's got that way from bad design or operator negligence. I'd vote on the latter.
1.* Wood anythings (other than Gar Woods, Hacker Crafts, and vintage Chris Craft runabouts) go for cheap.* GB woodies have always been pretty inexpensive.* For example, in 1998 when we bought our GB36, wood GB36s from the first half of 1973 were selling for perhaps $50k average.* Fiberglass GB36s from the second half of 1973 were selling for $80k to over $100k for a really, really nice one.

2.* I don't know these days.* At the time we were considering it the total cost would have been about $40k.* But you're right--- unless the original engines have failed, a repower just to repower is often not at all cost-effective. On a boat like ours, the cost of a repower would never even come close to being realized in the resale value.* One does it for one's own satisfaction, not because it makes economic sense.* Like putting a $20k paint job on a boat that's worth $50k at best, which I've seen happen.* It was important to the owner to do this.* The cost logic was not a factor.

3.* The FL120 and the FL135 do not share the same base engine.* They are very similar, but the base engine for the 120 was the Dorset and the base engine for the 135 was the Dover.* The Dover incorporates some significant improvements over the old Dorset.

The FL135 is in all sorts of boats.* Probably as many if not more than have FL120s.* There are several 1980s vintage GBs for sale in our marina right now that have FL135s.* FL135s were used in Krogens and many other makes.* Keith of this forum has an FL135 in his Krogen 42.* And don't forget the rest of the world.* Look at international boat ads and many of them will list the engine as a "Dover" engine.* A lot of companies around the world marinized both the Dorset and Dover engines.* Lehman was just one of them.

The Dorset (FL120) engine wasn't a lemon in the overall sense.* It was a piece of crap as a truck engine, but it proved to be extremely well suited for industrial and agricultural use.* For many years, Ford of England supplied all the diesel engines to Ford, including Ford in the US.* This is why you can still find agricultural diesel shops in the US that carry parts for the Ford Dorset engine (it didn't go by that name in the US).* Ford used the engine in their own farm tractors and they were supplied to a number of combine manufacturers.* For example, some folks on the GB owners forum recommend a totally non-marine outfit in the Midwest somewhere as the best place to get new injectors or have injectors rebuilt for the FL120.* This shop specializes in repairing agricultural equipment.* Much cheaper, apparently, than using a marine service to do the same work.

4.* Lehmans don't overheat unless they develop a problem or they are operated in a manner than helps create a problem.* So you're right, the cause of an overheat is often operator error, if you will.* Of course there can be non-engine problems that can cause an overheat, too, if the operator doesn't take immediate action.* This is what's happened to us a couple of times.* In both cases the engine temp began to climb because of a restriction in the raw water intake.* We saw what was happening right away and shut the engine down long before the engine was endangered.* The temperature climb in these cases had nothing to do with the type of engine--- it would have happened with any kind of engine.

The problem with the FL120 (I can't speak for the FL135 is that if the engine does overheat, its design and construction is such that severe damage can occur fairly quickly.* It will not tolerate an overheat condition very long at all.* From what I've been told, the head gasket will go very quickly if the engine is overheated, and the head is very susceptible to warping if the engine overheats.

*
 
If it was known (how could it not be) that they were weak then why did'nt Lehman get another engine to marineize?

Lehamns work great at trawler 2 -3-4 gph , no problem.

But if you think its a 135 HP engine that will produce 135 HP all day long , your going to have big problems.
 
80 ton Wooden full displacement Malahide ( 176, 000 # ) does 7.5 kn at 1400 rpm , 260 hp Volvo TMD 100

Will do that all day, reasonable seas . Haven't got a real handle on the mpg figures .
 
Orcades,
Sounds like you're powered just right. From what I've read, heard and otherwise ingested I usually say 3 to 5hp per ton. Five is probably more appropriate for smaller boats like my 30' Willard and three is more likely on the mark for larger boats. But there are some variables that trump displacement like usage, B to L ratio, wetted surface, PC and many others depending on the general design of the boat.

Three to five hp per ton applies only to FD craft. Boats like many of the DeFevers that aren't FD but fairly close can just plug in a little more power like 3.5 to 6.5 hp. It would not be as easy to guess how much more a CHB or GB would need. More to be sure but how much would take a better guesser than me or perhaps a NA that actually knows this stuff but even then it would be a range of power. Not a specific amount. However the range of power would not be very wide. As you get further from FD it can get rather wide. But once you reach planing one needs at least enough power to get up on plane at full load.

One of the best ways to make some conclusions for most of us is to compare lots of boats over time and observe their performance relative to their power and hull shape.
If you have two boats w the same WLL and the same displacement but one is short on performance there is some other reason for the difference. Sometimes obvious and sometimes not. A Camano 41 is quite an efficient boat for it's general type. My opinion on why that is so is that they are a light boat. Directly relateable to "HP per ton".

But my re to the OP .. 3 to 5 hp per ton.
My opinion.
 
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