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Old 01-11-2015, 07:53 PM   #21
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Indeed wadden and Mark.
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Old 01-12-2015, 07:48 AM   #22
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I am not sure either...
I have a 40 with a 120 Ford and best measurement I have is about a 34 foot waterline.
I am overpropped and live aboard with 2 so the boat is well loaded...but I dropped to a max of 120 gallons of fuel.
I run around 1650/1700 rpm and go 6.3 knots and burn 1.9gph for around 3.3 nmpg.
that's numbers averaged over the last 4 years and a little over 6000 miles/1200 or so hours.
I also have a 40 Albin with a 120 Lehman, but I am NOT over propped.
Also very heavily loaded. I run just about the same speed and RPM and I use about the same amount of fuel. We've compared numbers in the past and the difference in our calculated numbers is insignificant.
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Old 01-12-2015, 11:55 AM   #23
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Will twin 135 Lehmans on my 38 ocean Alexander burn a lot more fuel than a single diesel engine I normally run them at 1600 rpm or 7 Nts
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Old 01-12-2015, 12:24 PM   #24
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Of course ...
Two FLs are 760 cu in engine displacement. Far far more heat loss from combustion to sea water and/or air.
It gets complicated if you really get into it re engine friction ect.
But a lot of guys are running a twin on one engine and there are very few reasons to do that other than to reduce fuel consumption.
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Old 01-12-2015, 12:45 PM   #25
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Will twin 135 Lehmans on my 38 ocean Alexander burn a lot more fuel than a single diesel engine I normally run them at 1600 rpm or 7 Nts
Depends how YOU define "a lot more".
I would guess less than double, maybe 1.75 times as much.
Personally I do not consider that a lot more.
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Old 01-25-2015, 08:59 AM   #26
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The Albin 36 is what started this thread, it is a semi displacement hull for those who are not familiar. I am restoring a Hershine 37 which is popped out of the same mold. The original prop was a poor quality LH 24 X 17 as marked.

When measured at Kalenberg in WI it came in anywhere between 15" and 16". They brought it up to avg of 17" in class II standards, fine for a low rpm situation. It will be interesting to see how it preforms once I get the hull wet this spring with the 2:1 BW FL120.
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Old 01-26-2015, 05:42 PM   #27
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Greatlaker,
please give us an update on your results after having your vessel back to elements.
Do you have a single?


best regards / med venlig hilsen
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Old 01-26-2015, 06:13 PM   #28
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Quote:
Originally Posted by ocean View Post
Will twin 135 Lehmans on my 38 ocean Alexander burn a lot more fuel than a single diesel engine I normally run them at 1600 rpm or 7 Nts
I agree w jleonard but maybe a little less fuel at about 1.5 times as much. But the engines will be much less loaded using about 40hp out of 240hp.

The archives are full of threads on both issues but the more we talk about either issue the less important it seems.

But it's obvious if you want to go 7 knots and occasionally 8 the single is better until it quits.

A boat like that in my stable would have twin 55hp engines.
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Old 01-27-2015, 12:36 AM   #29
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I agree with Eric and expect the twin 135 to run at ~1350 rpm at 7 knots and to burn ~1.3 times more fuel at 7 knots than the single.
Since I personally prefer to reach hull speed at ~75% WOT rpm the optimum twins for this vessel were 80hp IMO.


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