# Fuel Consumption



## vega1860 (Dec 18, 2006)

We do not have a fuel gauge on Lealea so I keep meticulous records of engine hours and fuel added. Over time I have determined that our Yanmar 2GM20 will run 2.5 hours on one gallon of diesel fuel; 32.5 hours on the main tank and 25 hours in reserve. We generally cruise under power at 2800rpm and waddle along at about 6.5 knots in flat calm water.

When calculating how far we can get under power I usually use 4 knots because the water is not usually flat calm out there. Sometimes we have found we are going up and down as much as forward.

Looking over my logbook I see that, in over 3000 nautical miles covered, our total fuel consumption for 2011 has been 12.2 gallons 

Just wondering how others are managing fuel, other than just pretending the boat is a car and relying on the fuel gauge. Our friend Captain Wendell who operates a Vessel Assist boat out of Seattle tells us that out of gas due to faulty gauges is one of the most common reasons for help calls.


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## St Anna (Mar 15, 2003)

I do the same as you - only use engine hours and try and always keep tanks to the brim to reduce condensation. 

I did have fuel guages and as I could not trust them I removed them. I will cruise at about 2000rpm which gives us 6.5kn in most conditions and I adjust for seastate if it is rough. We have the Yanmar 4JH2-UTE. Usually rough seas means some breeze so we sail in that case. I hate the ride through seas if only under motor.

The last 'larger' section I did, I used the motor more than I wanted and after 750nm, I needed 50L.

Just mucking around the Bay, I will have used more than this - especially after my father decided the turbo needs to be used more~3400rpm.

As for the running out of fuel, well, hopefully not and even though I am almost in suburbia now, I still keep another 4 20L jerry's


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## vega1860 (Dec 18, 2006)

St Anna said:


> always keep tanks to the brim to reduce condensation.


Something we had to learn the hard way when we went north.


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## WanderingStar (Nov 12, 2008)

I don't have guages, I use a dipstick. I don't track my usage, but I filled the tanks two years ago. After daysailing often (50 times a year?) and a few overnight cruises, I added 20 gallons this year. I probably had not used more than 40 in two years. I do like the 12 gallon figure. My figures indicate probably a half gallon per daysail. The engine is a 4-107, the boat 16tons.


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## Boasun (Feb 10, 2007)

Your engine will use about 0.6 lb of fuel per horsepower an hour. Diesel is 7.13 lb per Gallon.

So with my boat's engine of 64 HP, it is: 0.6 x 64/7.13 will give my approximate fuel consumpion per hour of 5.39 gallons an hour. My tanks max is 180. I fill my tanks to 10% short of 180 which is 162 gallons and divide that with 5.39 gives me about 29 hours of operating time, considering the thievage of the height of the pickup tubes above the bottom of the tanks.
It is a good thing I have a ketch because the wind is free.


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## JedNeck (Sep 22, 2011)

Didn't use a drop all year...I have a big electric outboard motor though. 

I am a freak about MPG tracking in my car though. It's amazing what you can see just by watching fuel mileage.


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## WanderingStar (Nov 12, 2008)

Boasun said:


> Your engine will use about 0.6 lb of fuel per horsepower an hour. Diesel is 7.13 lb per Gallon.
> 
> So with my boat's engine of 64 HP, it is: 0.6 x 64/7.13 will give my approximate fuel consumpion per hour of 5.39 gallons an hour. My tanks max is 180. I fill my tanks to 10% short of 180 which is 162 gallons and divide that with 5.39 gives me about 29 hours of operating time, considering the thievage of the height of the pickup tubes above the bottom of the tanks.
> It is a good thing I have a ketch because the wind is free.


Only at max rpms I think. Even so, that seems high. I'm not disputing your figures, but my nominally 45 hp engine uses little over a gallon an hour at most, and usually less.


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## travlin-easy (Dec 24, 2010)

30-HP gasoline engine, 12,500-pound Morgan 33 O.I., slack tide running at 2,000 RPM, speed of 6.5 to 7.2 depending on bottom cleanliness, 1/2- GPH. This translates to 13 MPG, which I consider excellent fuel economy for this craft.

And, I always keep the fuel tank topped off. Condensation cannot form inside a tank that has no air inside.

Cheers,

Gary


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## Cruiser2B (Jan 6, 2011)

travlineasy said:


> 30-HP gasoline engine, 12,500-pound Morgan 33 O.I., slack tide running at 2,000 RPM, speed of 6.5 to 7.2 depending on bottom cleanliness, 1/2- GPH. This translates to 13 MPG, which I consider excellent fuel economy for this craft.
> 
> And, I always keep the fuel tank topped off. Condensation cannot form inside a tank that has no air inside.
> 
> ...


I have gas A4 and use about 1gallon an hour !. I usually cruise at 18-2000 rpm at 5.5knt. I love the little engine as it is quiet and reliable and freshly rebuilt...but it is a gas hog! We had a good sailing season and used about 25 gallons total. I will someday either have a beta diesel or electric conversion....


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## jrd22 (Nov 14, 2000)

We have a fuel gauge that reads for both tanks and both tanks have sight tubes (I use these more often than the gauge) and I track all fuel and hours just because I'm anal about not running out of fuel (tanks hold 190 US gal), which will probably guarantee that I'll run out at some point) Our old Volvo 62 hp consistently burns 1 gph at 2500 rpm which is a little over 6 knots through the water when calm. Wide open I"m sure it would use 3-4 gph.


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## tommays (Sep 9, 2008)

I run my A4 at 1500 RPM as it just stuffs the stern at more RPM to go a tiny bit faster while i have not done exact it is way under 1 GPH

To go from 5.5 to 6.5 knots most likely doubles the fuel burn as thats the point were it stuffs the stern with a 24' W/L


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## Rockter (Sep 11, 2006)

I use a dipstick, with a volume conversion chart.
I don't have a fuel guage.


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## addict (Apr 5, 2010)

My fuel gauge is an old batten. I normally watch my hours and start checking around 20-25 hours which is about half a tank. My old 2gm burns around 1.25-1.3 liters per hour @ 2400-2600 rpm.


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## JimsCAL (May 23, 2007)

I agree that Boasun's SFC estimate of 0.6 lb/hp-hr is a bit high. I would estimate something like 0.45 to 0.50 is closer. But the big thing to keep in mind is that you are typically running at FAR less than rated power. Power requirements vary approximately with the cube for a displacement hull. So reduce the speed by 20% and you cut the power (and fuel consumption) by half (0.8x0.8x0.8=0.512).


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## joethecobbler (Apr 10, 2007)

32' boat w/a 4ft draft full keel 10' beem 35 hp. kubota 4cyl w/ a hurth 125 2.73to1 ratio w/ a 19r11 three blade prop. gross weight 13-14000# burning less than 1/2 gal. an hour on flat water.

I think there are alot of factors that will influence the amount of fuel usage beyond just the engine size and operating speed. 
even the "freshness " of the bottom job would effect it.


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## SkywalkerII (Feb 20, 2008)

Moyer Marine sent out an email not long ago about a nice little upgrade for our beloved Atomic 4s. How about a new carburetor jet that reduces fuel consumption to 1/2 to 2/3 a gallon per hour! I haven't had the chance to follow up on this yet, but I'm looking forward to it.


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## LakeSuperiorGeezer (Oct 8, 2010)

*Lean running engine*



SkywalkerII said:


> Moyer Marine sent out an email not long ago about a nice little upgrade for our beloved Atomic 4s. How about a new carburetor jet that reduces fuel consumption to 1/2 to 2/3 a gallon per hour! I haven't had the chance to follow up on this yet, but I'm looking forward to it.


 If engine runs lean, could burn exhaust valves. I would leave as is.


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## travlin-easy (Dec 24, 2010)

LakeSuperiorGeezer said:


> If engine runs lean, could burn exhaust valves. I would leave as is.


Just about everyone I know that uses an A4 also uses a product called Marvel Mystery Oil, which is a top-cylinder lubricant that has been around for more than a half-century. It pretty much prevents valve burning, while at the same time aid in seating and sealing the valve and valve seals. You can still buy this product in most automotive stores and it is added to both the fuel and crankcase. I'm convinced that this product alone is responsible for keeping most A4s in good running condition, and at the same time helps boost fuel economy.

Cheers,

Gary


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