Gas usage

NOT Firewood · Post by **NOT Firewood** » Sun Sep 16, 2012 8:55 am

Can the rest of you let me know what a good average of a gas usage is? I am running my 23' skiff at about 4 gallon an hour this seams high to me.

farupp · Post by **farupp** » Sun Sep 16, 2012 9:39 am

I would be interested to know that, too, as in October I am taking a 120 mile round trip from Charleston to the Georgetown, SC, wooden boat show. My Sea Skiff has a single CC 283 V-8, and the boat will run at about 2800 rpm on a plane.

Also, is your usage of 4 gallons per hour in US gallons or Canadian gallons, if they are still different.

Thanks.

Frank

Oberon01 · Post by **Oberon01** » Sun Sep 16, 2012 10:00 am

I will be using my 1965 24' Skiff with the original 327 extensively this week at the International Show pre-events in Missouri. I will try to get an idea of consumption, we are on several long cruises. The boat will likely be pretty heavily loaded. I think it is more than 4 gallons per hour, based on my experience with it in recent years. I have kind of wondered myself about consumption rate.

drrot · Post by **drrot** » Sun Sep 16, 2012 10:41 am

Paul,
Don't use "I'm testing consumption" As an excuse for running out

mfine · Post by **mfine** » Sun Sep 16, 2012 10:58 am

With a SBC V8 running moderately rich of peak, expect to burn 8-10 gallons per hour for every 100 hp produced.

So, for a 283 think about 15-18.5 gph at full throttle depending on how efficiently tuned your carb is.

Figuring half the speed takes about 1/4 the power, give or take (on plane) and you can see how fuel consumption is going to be very sensitive to throttle position. Just a few mph slower can be several gph less fuel burned.

Oberon01 · Post by **Oberon01** » Sun Sep 16, 2012 11:07 am

we usually cruise our Sea Skiff at around 2500 rpm, just "feels" like a comfortable engine and water speed. I have never tested consumption but we all know what M Fine suggests - slight engine speed increases can mean lots more fuel burned.

Personally, I would think 4gph at a reasonable engine speed is acceptable for these rather crude engines pushing a round-bottomed Sea Skiff.

NOT Firewood · Post by **NOT Firewood** » Sun Sep 16, 2012 6:55 pm

Well I had hope that something was wrong, but it sound like i am in the ball park. As for 4 gph this was a rough conversion fron 17 liters per hour. I am am also running a 305. Generally running @ 3000rpm with 4 passengers. Paul let us know what you get.

evansjw44 · Post by **evansjw44** » Mon Sep 17, 2012 8:38 am

How the hours are measured makes a big difference. If you use the hour meter on a CC mechanical tach then hours are only correct at 2500 RPM (mid scale) Above 2500 the hours are proportionally shorter below they are longer. Hence above 2500 your GPH computed from tach hour is lower than true.

I have fuell flow meters on my 327Fs and at 2800 revs I'm burning 8.5 - 9.0 GPH each engine.

farupp · Post by **farupp** » Mon Sep 17, 2012 9:04 am

Jim, is that for both engines running or just one?

Frank

mfine · Post by **mfine** » Mon Sep 17, 2012 10:15 am

Fuel consumption at a given RPM is going to vary considerably with the torque required, in other words the prop used and boat weight and drag. Comparisons require very similar boats.

gbraker · Post by **gbraker** » Mon Sep 17, 2012 3:26 pm

Gallons per hour are only part of the story. How far did you go, current and wind conditions are also a factor. Many times you burn more fuel on plane, but you also go a lot further. There is always a sweet spot. You get on plane, then adjust the trim tabs and the throttles so that you get just enough RPMs to stay on top. My 30 ft Connie with 327fs was most efficient around 2K RPM.

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