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Old 10-24-2011, 03:50 AM   #21
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RE: Lehman 120 FloScan readings

A FloScan will tell you much more than just your fuel flow but having accurate fuel flow info is enough reason to have one

They work great as a fuel gauge too, if you know your tanks capacity.
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Old 10-24-2011, 09:03 PM   #22
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RE: Lehman 120 FloScan readings

This question has been raised in other posts, but in relation to the flow scan figures posted here, how would you expect the consumption to differ if the boat was running twin FL120 insead of a single. I seem to remember that the consensus was with a twin set up, each engine would use approximatly 30% less fuel for the same RPM/MPG figures.

Is this a valid assumption?
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Old 10-25-2011, 05:23 AM   #23
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RE: Lehman 120 FloScan readings

Quote:
nomadwilly wrote:
While you guys are roll'in around on the ground think'in how clever you are you should consider the fact that all your numbers are meaningless without knowing if Ken's boat has been propped properly. If he's overpropped even 100 rpm ...fuel burn at 1750 on your boat could be way different than his. Ken's numbers will only be valid if you're propped just about exactly the same as he is and have a boat very very similar in displacement and shape. On the bright side you can tell quite a bit about what happens to the burn rate if you increase or decrease say 100 or 200 rpm.
*all i can say* is it gave me the info to help me save a little fuel
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Old 10-27-2011, 11:16 PM   #24
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RE: Lehman 120 FloScan readings

This post has got me doing the figures(estimates) on our IG 36.We only have sight lines, using some of the above figures and my own observations, plus some of Marin's observations from his GB 36, which is very similar in set up to our boat.

I am amazed that between 1500 & 2000 RPM we increase boat speed by 1.3 knots with a corresponding 98% increase in fuel consumption! Do any other twin Lehman owners find this plausable?
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Old 10-27-2011, 11:30 PM   #25
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RE: Lehman 120 FloScan readings

I find it plausible but we've never run any tests to determine fuel consumption increase between various rpm. A GB is no different than any other similar semi-planing boat--- you can run them faster than hull speed but the fuel penalty is significant.

This is somewhat apples and oranges, but in the GB 42 ads of the 1990s when they were still making the boat, peformance figures included in the ad called out an "economic" cruise speed of some nine knots with a fuel consumption of seven or eight gallons per hour (twin engine, 400-something hp Cats). However the boat could be cruised "comfortably" at some 14 or 15 knots with a fuel consumption of some 23-24 gallons per hour. So less than twice the speed at three times the fuel consumption.
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Old 10-28-2011, 08:05 PM   #26
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RE: Lehman 120 FloScan readings

Andy, you are most likely exactly on the mark. I don't have my numbers with me now, but when I return in the spring (May 2012) I'll update this and give my speed numbers for each rpm range, which again, won't match anyone else, but will give an idea of fuel use/speed on my single. I cringe when someone posts that they usually run at "80% rpm" (2000 rpm or more) on a Lehman 120. You've got to be in a real hurry to want to burn that much fuel. And if you're in a hurry, you shouldn't be driving a trawler.
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