Twin Lehman 135's

I recently picked up my 1986 Albin 40 Trawler. It has twin Lehman 135's.

I was wondering if the sage members here with experience with these engines or with similar boat experience might weigh in about fuel consumption.

We did about 250 miles and consummed about 250 gallons.

Consumption rate was just shy of 10 gallons per hour. We ran against the tide a lot of the time, averaged about 8.6 KNOTS speed so I expected higher fuel consumption but this was beyond what I estimated.

I wonder what consumption might drop down to if we averaged 7 knots.

Any other input would be appreciated.

I have Lehman 225’s and I run 1650 RPM which gives me 8.5 kts. I plan on about 5 gph. For us, that means if we are doing an 8 hour trip, we’ll usually make it two 4 hour days with an overnight in an anchorage. 5 gph seems to be a good number for fuel planning. This also includes our generator running the entire time, even underway.

Yeah, I think if we were in the 1650 - 1750 rpm we would have faired much better in the GPH consumption department.

How clean is the running gear and bottom? We have a single SP135 so I can’t compare gph but I know from experience that with a fouled bottom/running gear our fuel economy goes down significantly.

They are nice engines though.

Zoar said:

Yeah, I think if we were in the 1650 - 1750 rpm we would have faired much better in the GPH consumption department.

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That’s the sweet spot for our single.

We had twin FL120s in our last trawler and planned 2.5 gph per side (5 gph total) at 1650 - 1700 RPM which gave us about 7 - 7.5 knots (full displacement hull speed). Anything higher than that would only marginally increased speed but really pushed a lot of water out of the way!

Much appreciated.

Yes I will try 1650 to 1750 rpm and see what we get for consumption.

(BTW--Bottom is totally clean, it was just put in the water the day before our 250 mile trek.)

Yep, pushing a 40' to 8.6kts is not going to be very efficient. Try slowing down to like 7.6, burn rate will drop a good bit.

Congrats on your new boat. We do need some photos though.

1500 rpm in my IG36 FL120s seemed a sweet spot using 12-16L/hour. At 40ft you may need the extra rpm, but "speed return on fuel investment" is highly disproportionate as you up the rpm.

We have twin Lehman 120s in a 56,000# DeFever. We consume 3.5 GPH at 1,650 RPM which generally gives us about 8.5 MPH.

You didn’t say what rpm you were running for that 8.6 against the current but you certainly can run a 135 hard enough to consume 5 gph. I find that my Lehman 135s follow the published fuel use curves pretty closely until I start to push hull speed. I normally cruise at about 1800 rpm for 8.5 knots which is starting to push my hull speed and yields about 5-6 gph combined. Of course if one is fighting current or heavy seas the fuel used for a given speed will be higher - sometimes considerably higher.

Ken

BruceK said:

1500 rpm in my IG36 FL120s seemed a sweet spot using 12-16L/hour. At 40ft you may need the extra rpm, but "speed return on fuel investment" is highly disproportionate as you up the rpm.

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Hi BruceK,
Roughly what knots were you avg. at 12/16 lts p.h. please.

U r pushing too hard, theoretical hull speed is not your most fuel efficient. Pull the throttles back until engines feel & sound easier (speed will depend on Tidal current). u should be in the 4-7 gph range probably only making 7 knots or so

bogranjac1 said:

Hi BruceK,
Roughly what knots were you avg. at 12/16 lts p.h. please.

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7-8 knots I think, the IG GPS was set metric, so it`s a guess

You should be easily able to get down to 4 gph total and lose maybe a knot.

Slow it down, you will double your fuel economy.

Based on my 36 foot Albin I would guess your 40 foot weighs around 35,000 pounds, loaded.

pete

We run 1650-1700 at 7 knots. With a clean bottom and a slightly oversized prop I regularly get 2gph or less.

We hold 400 gallons of fuel and 200 water. Running lean on those and I pick up a knot.

If I got my wife's junk off might pick up another knot....

Sorry, that's with a 135 single.