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Old 10-23-2012, 07:59 PM   #1
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Lehman 135 Cruise RPM

What RPM do you use for cruising and what fuel comsuption to you get?

I'm fairly new to the forum and trawlers. We have had our 1988 Marine Trader DC for just a month. It has a Ford Lehman 135 engine. I've not seen many posts regarding this combination, but like I said I've only been here a short time. A lot of posts on the Lehman 120, not so many on the 135.

The PO said he cruised at 1200 RPM and got 3 GPH. The RPM seems low to me and the GPH high based on readings in the forum and the power curves in the engine manual. With only a few hours on the water so far I haven't gotten my own data yet and I'm hoping some other forum members have the same engine and can give me some numbers based on experience with similar boats.

Thanks all.
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Old 10-23-2012, 08:08 PM   #2
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What RPM do you use for cruising and what fuel comsuption to you get?

I'm fairly new to the forum and trawlers. We have had our 1988 Marine Trader DC for just a month. It has a Ford Lehman 135 engine. I've not seen many posts regarding this combination, but like I said I've only been here a short time. A lot of posts on the Lehman 120, not so many on the 135.

The PO said he cruised at 1200 RPM and got 3 GPH. The RPM seems low to me and the GPH high based on readings in the forum and the power curves in the engine manual. With only a few hours on the water so far I haven't gotten my own data yet and I'm hoping some other forum members have the same engine and can give me some numbers based on experience with similar boats.

Thanks all.
Agreed.... my charts say 1200 rpm should only be about 1.0 GPH...

3.0 GPH shouldn't occur till over 2000 rpm which my boat has proven to me.

I plan on cruising around 1600-1700 RPM so I get slightly less than 2.0 GPH and hopefully somewhere's around 6.5-7.0 knots and average around 4.0 NMPG
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Old 10-23-2012, 08:08 PM   #3
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What RPM do you use for cruising and what fuel comsuption to you get?
I have 120s so leave it to 135 owners to respond, but I doubt the modest output difference changes things much. Meanwhile, you could ask ever helpful American Diesel,the effective successors to Lehman. BruceK
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Old 10-23-2012, 09:44 PM   #4
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1200 rpm seems too low for a good cruise rpm. I don't know that the engine would even get up to the right temperature. The best cruise rpm envelope for the older FL120 is 1500-1800. We cruise ours at 1650 and we get about 2.5-3 gph on each engine. I would think the FL135 is somewhat similar.
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Old 10-23-2012, 09:59 PM   #5
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What RPM do you use for cruising and what fuel comsuption to you get?

I'm fairly new to the forum and trawlers. We have had our 1988 Marine Trader DC for just a month. It has a Ford Lehman 135 engine. I've not seen many posts regarding this combination, but like I said I've only been here a short time. A lot of posts on the Lehman 120, not so many on the 135.

The PO said he cruised at 1200 RPM and got 3 GPH. The RPM seems low to me and the GPH high based on readings in the forum and the power curves in the engine manual. With only a few hours on the water so far I haven't gotten my own data yet and I'm hoping some other forum members have the same engine and can give me some numbers based on experience with similar boats.

Thanks all.
I have twin 135's and find that my two "sweet spots" are at 1600 RPM (4-5 gph I estimate) and 2200 RPM when I am in a hurry
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Old 10-24-2012, 08:18 AM   #6
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We have the SP135 and cruise 400 plus hours per year. I calculated our annual average speed which is anchor to anchor and gallons per hour (plus a bunch of other meaningless numbers). I have a 4 year average of 6.3 knots at 1.7 gallons per hour. We displace 44,000 lbs with a 37 foot water line and run with paravanes which cost us between 1/2 and 3/4 of a knot. Our sweet spot on the engine is 1600 to 1800 rpms.
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Old 12-20-2014, 12:47 PM   #7
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I am also to new to this to post GPH date but my Universal 36 with a single American Diesel Corp 140 HP feel right at 1650 and give me about 7.5 K GPS speed
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Old 12-21-2014, 04:52 PM   #8
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I must have the pig of the fleet to only get 6.3 knots at 1650 rpm at 34 lwl and a 120 lehman.
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Old 12-21-2014, 06:24 PM   #9
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I must have the pig of the fleet to only get 6.3 knots at 1650 rpm at 34 lwl and a 120 lehman.
No, you're honest.
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Old 12-21-2014, 06:45 PM   #10
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No, you're honest.
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Old 12-21-2014, 07:04 PM   #11
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Unless you're propped other than rated rpm cruise rpm will be all over the place. Or if you're propped correctly you may hear others saying they cruise at some rpm considerably lower than you do and go faster than you. So unless you know the other guy is propped the same as you any rpm numbers he calls out are basically meaningless.

Find someone with the same WOT rpm and then compare other rpm performance points.
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Old 12-21-2014, 07:09 PM   #12
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Unless you're propped other than rated rpm cruise rpm will be all over the place. Or if you're propped correctly you may hear others saying they cruise at some rpm considerably lower than you do and go faster than you. So unless you know the other guy is propped the same as you any rpm numbers he calls out are basically meaningless.

Find someone with the same WOT rpm and then compare other rpm performance points.
Some of us are experienced/smart enough to extrapolate a few hundred rpm. Even if the same or up/down...my boat isn't going anywhere near 7 plus knots at a comfortable cruise rpm and wavemaking becomes obvious suggesting a lot more power.
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Old 12-21-2014, 08:17 PM   #13
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I wonder if transmission and prop variances could cause much of a difference?

If two boats had the same engine could they have different transmission (ratios) and therefore very different props?

Is big and slow better for a slow boat prop wise?
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Old 12-21-2014, 08:39 PM   #14
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I wonder if transmission and prop variances could cause much of a difference?

If two boats had the same engine could they have different transmission (ratios) and therefore very different props?

Is big and slow better for a slow boat prop wise?
I am running a bigger prop than some 40 Albin owners and seem to be off a tad on economy...but that could easily be a few things.

I am just wondering why so many shorter trawlers of similar design go a knot faster with better economy...based on more than a few posts I have read.

Bottom line..over or under propping a few hundred I seriously doubt would change upwards of 15-20 % economy. Yet boats are reporting 7+ knots and less than 2 gal per hr burn where I am 6.3 kts at around 1.9 gal per hr.

No matter what prop, tranny, total weight, etc...I have a hard time seeing that big of a difference....u less my engine is extremely inefficient or someone's numbers aren't measured too accurately.
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Old 12-21-2014, 09:18 PM   #15
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I have the Lehman Super 90s which is the 4 cylinder version of the 135. The sweet spot is right around 1650 rpm.
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Old 12-22-2014, 07:35 AM   #16
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No, you're honest.

Remember in High School when so many had a "12 second" car... Verified with a Timex and rattle can sprayed finish line measured with an odometer on a car??😎😎😎👍


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Old 12-22-2014, 07:37 AM   #17
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The PO said he cruised at 1200 RPM and got 3 GPH. The RPM seems low to me and the GPH high based on readings in the forum and the power curves in the engine manual. With only a few hours on the water so far I haven't gotten my own data yet and I'm hoping some other forum members have the same engine and can give me some numbers based on experience with similar boats.
The 1200 RPM and 3 GPH are not consistent with my experience on a Krogen 42 with a Lehman 135. We operate at 1600 RPM and get substantially better than 3 GPH.
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Old 12-22-2014, 07:54 AM   #18
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Originally Posted by LarryBud49 View Post
What RPM do you use for cruising and what fuel comsuption to you get?

I'm fairly new to the forum and trawlers. We have had our 1988 Marine Trader DC for just a month. It has a Ford Lehman 135 engine. I've not seen many posts regarding this combination, but like I said I've only been here a short time. A lot of posts on the Lehman 120, not so many on the 135.

The PO said he cruised at 1200 RPM and got 3 GPH. The RPM seems low to me and the GPH high based on readings in the forum and the power curves in the engine manual. With only a few hours on the water so far I haven't gotten my own data yet and I'm hoping some other forum members have the same engine and can give me some numbers based on experience with similar boats.

Thanks all.
Is it possible he meant 3 MPG and not GPH? That would make a little more sense.
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Old 12-22-2014, 08:07 AM   #19
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The 1200 RPM and 3 GPH are not consistent with my experience on a Krogen 42 with a Lehman 135. We operate at 1600 RPM and get substantially better than 3 GPH.

Marty, Our KK42 has the Lehman 135, and we have a lot of documentation from prior owners that says 2080 is the ideal RPM. We haven't operated her much...just the three days from Kent Island to Hampton VA...but we ran just under 2000 and 7 to 7.5 knots. The PO told us we'd burn 2.5 GPH with the gen running for heat. Mike


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Old 12-22-2014, 09:45 AM   #20
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Cruising up to about 80% of max RPMs is usually cited as reasonable. Our twin 135's seem to have a sweet spot right around 1800-1900 which is just a bit under the theoretical 80% of 2000. I use 1800-1900 because we're running 8-9 knots and above that we are starting to exceed hull speed so our fuel consumption goes way up.

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