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Old 11-09-2011, 07:16 PM   #1
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real world fuel usage 120

Ok so here are some real world differences** I just arrived tonite in hollywood fl from the chesapeake bay* I read the post 2bucks started with his flow scan readings* My boat is a 1973 34' marine trader* with a 21''x16 p 4 blade prop tru 2-1 gears** This is my 4th trip to s fla app 1270 miles* So total 7 laps considering up and back* First year I cruised at 1800 rpm used 2.5 gph and the trio took 1910.2 hrs stoped for fuel 3 times** In 09 i slowed to 1700rpm trip took184hrs wit fuel usages of 2.25to 2.38gph* this year I slowed to 1550rpms* trip took 205 hrs fuel usage was 1.75 grh and I had to stop only twice for fuel** I really did not think the 120 lehman could use so little fuel** For me it was a decent $ savings* You be the judge for your self

*thanks 2bucks
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Old 11-09-2011, 08:05 PM   #2
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RE: real world fuel usage 120

The fuel savings is nice but the truly amazing thing is that by reducing your engine revs you reduced your trip time from 1,910.2 hours to only 205 hours.

:-)
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Old 11-09-2011, 08:14 PM   #3
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RE: real world fuel usage 120

ha you got me me 191.2 hrs
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Old 11-09-2011, 08:18 PM   #4
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RE: real world fuel usage 120

Rats. I thought you'd discovered a whole new way to vastly speed up a cruiser while reducing the fuel burn.
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Old 11-09-2011, 09:20 PM   #5
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RE: real world fuel usage 120

Quote:
motion30 wrote:


Ok so here are some real world differences** I just arrived tonite in hollywood fl from the chesapeake bay* I read the post 2bucks started with his flow scan readings* My boat is a 1973 34' marine trader* with a 21''x16 p 4 blade prop tru 2-1 gears** This is my 4th trip to s fla app 1270 miles* So total 7 laps considering up and back* First year I cruised at 1800 rpm used 2.5 gph and the trio took 1910.2 hrs stoped for fuel 3 times** In 09 i slowed to 1700rpm trip took184hrs wit fuel usages of 2.25to 2.38gph* this year I slowed to 1550rpms* trip took 205 hrs fuel usage was 1.75 grh and I had to stop only twice for fuel** I really did not think the 120 lehman could use so little fuel** For me it was a decent $ savings* You be the judge for your self

*thanks 2bucks
2Bucks, that is some GREAT information and with so many miles travel it would make for some very accurate readings! I have gotten in the habit of running my 135's at 1600 RPM (:smile, it feels good and I am sure it improves my fuel consumption.
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Old 11-09-2011, 10:35 PM   #6
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RE: real world fuel usage 120

If I'm reading this right there must be other factors in play here.

1800rpm= 191.2 hours @ 2.5 gph
1700rpm= 184 hours @ 2.25-2.38 gph
1550rpm= 205 hours @ 1.75 gph
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Old 11-10-2011, 05:10 AM   #7
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RE: real world fuel usage 120

Andy, I think weather conditions probably came into play there, but it is interesting that overall the time was so little different as a percentage, (about 7%). Motion30 you have a sister-ship to mine, only it is even older, mine being a 1975 hull. I find the sweet revs/speed about 1700rpm by feel and sound and bow-wave, but the significant saving is the extra cutting back to the 1500rpm region by the looks. I don't have a fuel flow meter, but I assume yours is the std Lehman 120, so the reading should translate to mine.
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Old 11-10-2011, 06:53 AM   #8
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RE: real world fuel usage 120

Quote:
shrimp wrote:
If I'm reading this right there must be other factors in play here.

1800rpm= 191.2 hours @ 2.5 gph
1700rpm= 184 hours @ 2.25-2.38 gph
1550rpm= 205 hours @ 1.75 gph

*The first year I stoped at marinas every nite** , second year just anchored most nights perhape the in and out of marinas accounts for* some of the extra time
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Old 11-10-2011, 08:18 AM   #9
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RE: real world fuel usage 120

Old fart
this if the first year I was not in a rush to get south, but still traveled alone so.. Coco beach was nice, st augestine. Myrtle beach is cool. The wind blew the whole trip not to much of a problem but all the big boats were inside everything from 65' sport fish to 120' MY Its funny the same parade of boats passing me everyday
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Old 11-10-2011, 11:22 AM   #10
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RE: real world fuel usage 120

You guys may be overlooking something very important. Even a fairly small difference in the way you load your engine will make considerable differences in fuel consumption at specific engine speeds. If your WOT rpm is 2500 (as it should be w a Lehman) and another boat is 2300 your fuel burn will be way different at most engine speeds. So if you're going to compare your fuel burn it can't be apples and apples unless both boats have the same WOT rpm. You may come close comparing fuel burn at a certain number of rpm down from your WOT rpm. So if you want to compare the 2500rpm engine boat w the 2300rpm boat compare at 1900rpm on the 2500rpm boat and 1700rpm on the 2300rpm boat. But it's best to compare boats that are propped the same.*
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Old 11-10-2011, 12:36 PM   #11
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RE: real world fuel usage 120

Quote:
Old Stone wrote:
OK Mike - How many days for the whole trip? If you are travelling alone, how many hours a day at the helm? I'm jealous!
*The trip this time of year is 18-20 days* usually sun up to sun down* before the time change,** there was enough day light about 715 am to get underway*to *and by 630 you better have your anchor down** On some days I was tired*and *maybe stoped a little eariler* In the spring the return trip is around 14-15 days due to longer days* of course one must allow for weather* this year I lost 2 day one on the chesapeake and one in Nc* due to strong wind and waves** still it s really cool trip*** you should try it
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Old 11-10-2011, 12:39 PM   #12
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RE: real world fuel usage 120

Eric the point here was not to say* somebody elses* fuel burn*will be x** but just there is a savings to be had by slowing down if you can.* I am sure every boat is different,* mine is just one example* I never thought my boat would ever burn less the 2gph* but it did* for 1200miles
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Old 11-10-2011, 02:28 PM   #13
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RE: real world fuel usage 120

When I did my "maiden voyage delivery" trip it was 530 miles and I burned less than 2 GPH with my 120 Lehman. Most of the time I was at 1700 or 1600 rpm.

That includes*a fair bit of idling time in the locks and waiting for a bridge or two.
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Old 11-10-2011, 04:36 PM   #14
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RE: real world fuel usage 120

Jay,

Sounds like you are/were propped right as that seems like good fuel consumption for that engine speed. I think Marin experienced a reduced burn rate at a higher rpm when he repitched his props. Lower load = less burn.
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Old 11-10-2011, 05:42 PM   #15
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RE: real world fuel usage 120

Quote:
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Jay,

Sounds like you are/were propped right as that seems like good fuel consumption for that engine speed. I think Marin experienced a reduced burn rate at a higher rpm when he repitched his props. Lower load = less burn.
*Yes I can "just" get 2500 rpm at WOT (with calibrated tachometer).
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Old 11-11-2011, 05:32 AM   #16
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RE: real world fuel usage 120

My motor will only turn 2150rpm in gear or neutral at the dock but runs very solid
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Old 11-11-2011, 05:39 AM   #17
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RE: real world fuel usage 120

Your "thottle" cable or speed stop needs to be adjusted.
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Old 11-11-2011, 09:09 AM   #18
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RE: real world fuel usage 120

Verify your tach before you start looking for problems you may not have.
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Old 11-11-2011, 10:05 AM   #19
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real world fuel usage 120

Unless the tach needle (assuming it is an analog tach) physically seizes up at 2150, it is a governor issue.

If the needle did seize but the engine accelerated to high idle rpm it would be obvious by the sound.


-- Edited by RickB on Friday 11th of November 2011 11:06:49 AM
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Old 11-11-2011, 10:51 AM   #20
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real world fuel usage 120

two tachs both agree probably governor adjustment I see the stop on the pump but would have to remove the inj pump to get to it


-- Edited by motion30 on Friday 11th of November 2011 11:52:33 AM
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