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First String
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Discussion Starter #1
So, I sail in Beaufort Sc. I have always got a current to run with or fight into. Who can I get a somewhat accurate figure on my gallon per hour fuel burn? I have a C&C30 MK1. If I was in still water I think I could tell with a gps 5 miles marked off and a gallon jug. But, how to tell with a canceled 20 gal tank and a 2 knot currant. What is the normal method for this? I just installed this engine a month or so back and would like to know how much it burns.

Hull Type: Fin w/spade rudder Rig
Type: Masthead Sloop
LOA: 30.00' / 9.14m LWL: 24.92' / 7.60m
Beam: 10.00' / 3.05m Listed SA: 459 ft2 / 42.64 m2
Draft (max.) 5.00' / 1.52m Draft (min.)
Disp. 8000 lbs./ 3629 kgs.
Ballast: 3450 lbs. / 1565 kgs. SA/Disp.: 18.42
Bal./Disp.: 43.12% Disp./Len.: 230.78
Yanmar 2gm20F

Thanks
LT
 

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I believe the only way is to top off the tank, motor several hours at cruising throttle, then top off the tank.

You don't need a gps, and the current has no effect whatsoever on gallon-per-hour calculations.
 

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Put a few gallons in a bucket and weigh it. Run at x rpm for one hour pulling fuel from the bucket (and returning fuel to the bucket). After one hour weigh the bucket again. The difference is fuel used/hr.
 

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old guy :)
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We keep track of all the hours of running and all the gallons of fuel.
From there it is really simple math.

Let's see, we had the diesel running for about 200 hours this summer and used about 100 gallons of diesel. 100 divided by 200 comes out to about 0.5, so I guess that equates to about 1/2 a gallon an hour.

As the youngens say, "You do the math."

Rik
 

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Do you have an hour meter on your engine? Most do, or should have. What I do is keep a log of the engine hours and fuel fills. So if I put 20 gallons in the tank, an cruise for a few weeks, then put 30 gallons in the tank, that gives me a general idea, as long as I keep filling to the same spot (i.e. always filling up, or always filling to 1/2 tank, etc.).


This is just one data point and it won't be terribly accurate since you are probably not running your tank dry and filling it all the way up and your fuel gauge is only so accurate (if you even have one). However, if you keep a running log, eventually your average gal/hr burn calculation will become more and more accurate. The more data points you have the closer your 'running average' will get to your true gal/hour burn rate.

So, just log your fuel fills against your engine hours.
 

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We keep track of all the hours of running and all the gallons of fuel.
From there it is really simple math.

Let's see, we had the diesel running for about 200 hours this summer and used about 100 gallons of diesel. 100 divided by 200 comes out to about 0.5, so I guess that equates to about 1/2 a gallon an hour.

As the youngens say, "You do the math."

Rik
The problem there is that I tend to do quite a lot of idling and low-rpm stuff, so my average is about 0.5 gals per hr. But the consumption at cruising throttle comes out to 0.8 gals per hr. I actually use 1 gallon per hour for trip planning.

The key here is to avoid any nasty surprises on a passage. Assuming too-high fuel consumption never hurt anyone.
 

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Your 16 hp Yanmar will burn 0.8 gal/hr full throttle, however!; fuel consumption is proportional to the power developed which is proportional to the cube of engine revs.
If you are at 1/2 the revs you reduce the power and hence fuel consumption by 1/8.

Let's say you are at 80% of max. revs. Then your fuel consumption will be 80% X 80% X 80% = 51.2% of the max:: 0.51 X 16 = ~8.2 hp. You just reduced your fuel consumption by a half.
Dick
 

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lt-
First you go out and procure a five or ten gallon jerry can. Or a series of 5 or 10 one-gallon cans or bottles. We can argue "fire marshal approved" elsewhere.
If you can start and end AT the fuel dock, you don't need the jerry cans. If you need to stop and return to some other point, you use the jerry cans instead.

Now you fill up the tank on the boat, at the fuel dock, after filling those jerry cans. Take an hour or three's run "out and back" in a straight line, preferably with the current turning at the turnaround point so you've done 1/2 with the current and 1/2 against, ending up back at the fuel dock again.

Fill boat, fill jerry cans if needed, make out-and-back trip, refill boat.

If that was a the fuel dock you can just read the pump to see how much fuel you burned, divide by the number of hours your ran. If you use the jerry cans...same thing, just note carefully how much was needed to refill the tank.

However you do the details, it is just "fill, run, clock, fill, measure."

The fun comes in if you want to try measuring fuel burn under adverse conditions, i.e. against wind and waves and under high throttle, you might double your casual flat-water consumption. An operator's manual for your boat might show the recommended cruising rpm and fuel consumption, along with a chart showing how fuel consumption tends to skyrocket as you increase rpm or load.
 

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First String
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Discussion Starter #12
lt-

If you can start and end AT the fuel dock, you don't need the jerry cans. If you need to stop and return to some other point, you use the jerry cans instead.

Now you fill up the tank on the boat, at the fuel dock, after filling those jerry cans. Take an hour or three's run "out and back" in a straight line, preferably with the current turning at the turnaround point so you've done 1/2 with the current and 1/2 against, ending up back at the fuel dock again.

Fill boat, fill jerry cans if needed, make out-and-back trip, refill boat.

If that was a the fuel dock you can just read the pump to see how much fuel you burned, divide by the number of hours your ran. If you use the jerry cans...same thing, just note carefully how much was needed to refill the tank.

However you do the details, it is just "fill, run, clock, fill, measure."

.
I have the face dock with fuel. So this might work out the best. Mid flood tide going out and turn around with the tide and run with the tide back. Yea that will do it.

That way I will not have to worry with having to bleed the lines.However I need to drain and clean that tank at some point.

Thanks for the help..
 

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Courtney the Dancer
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Just figure .5 gph, that's my guess, and it's probably a bit less so you'll have a reserve. Keep track of all your hours and the total gallons used. Do the math once in awhile and you'll have your average.
 

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I run .5 gph at just under hull speed 6k). 25 hp and 13000 lbs gas engine 1200 rpm 1:1 drive. Don't know prop pitch
 

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Rough guide

Diesel - 0.1 litres (0.026 US gal) / hp / hour
Gasoline - 0.3 litres (0.079 US gal) / hp / hour

At 5 knots through the the water.
 

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I have a 2gm20 on my Hunter 30 and have monitored my fuel consumption for the last two years.

The chart I posted seems pretty accurate.

I generally run my engine at 2000 rpm and have a consumption rate of 1 Liter per hour. ( 0.264 USGal/hr)

Obviously the consumption rate goes up as I increase RPM. Speed is dictated by other factors. With no wind I can motor at close to 5 knots at 2000 RPM.

Going into a 30 knot headwind I was barely able to make 2 knots at 2500 RPM and I was consuming over 1.5 Liters (0.4 USGal) per hour.
 

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I have the face dock with fuel. So this might work out the best. Mid flood tide going out and turn around with the tide and run with the tide back. Yea that will do it.

That way I will not have to worry with having to bleed the lines.However I need to drain and clean that tank at some point.

Thanks for the help..
What has the tide got to do with it?
 

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First String
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Discussion Starter #19
I will fight the tide going out and then come back with the incoming tide. Its only has to do with me doing a 3 hour round trip. nothing to do with this math.
 
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