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Old 01-03-2011, 09:26   #1
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Okay, it Was All My Fault . . .

Cruising from FL to the Abacos, under the power of the mighty Yanmar just south of Sale Cay......when she quits running. Wife and kids no longer smiling. No problemo....most likely contaminated fuel, simply empty out the fuel filter and it's off to the races again. Fuel filter was gunked up, but not too bad. Hmm....when I try to manually prime the system, it won't. Yep, outta fuel! But I filled it up myself not even 150 miles ago!! (How can that be?)

So we sail, upwind, all day against the current and make almost no headway. We throw the hook over about 3 miles off of Fox town, where there's plenty of diesel. The next morning I take my daughter with me in the dink (you know, the one with the motor that's been sitting for months, along with the gas, in the garage?). We make it 2.9 miles before THAT motor quit. So I paddle up to the dock, spend the rest of the playing Mr. Fixit while downplaying my idiocy.

Lessoned learned...at 80% rpm, you burn what you think you should be burning. At 95% rpm, you gain 1/3 of a knot and burn as much as a Hummer. It was my wife that figured it out, btw. Oh...and clean petrol is as important as an understanding wife.
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Old 01-03-2011, 09:38   #2
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Re: Okay, it Was All My Fault . . .

My Yanmar 4JH burns just shy of 1/2 gallon an hour pushing me at 5 kts. I rarely ever go faster than that and have determined that that is my economy cruise speed.

I've seen where I can buy a fancy meter thingy to hook up to my Garmin chart plotter that will monitor fuel flow and tell me what I already know for free...

It sounds like you still had a fun trip and the adventure continues!
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Old 01-03-2011, 09:52   #3
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Re: Okay, it Was All My Fault . . .

You found out the hard way about diesel fuel consumption. Yanmar publishes fuel consumption curves for all of its engines. Mine at recommended 80% cruise RPM burns about 3/4 of a gallon per hour, but at maximum continious power burns well over 2 and at full speed burns 5 according to the fuel consumption curve. In reality I find the curve to be pretty accurate, though I have not made much of an effort to test the upper limits. I once was forced to use maximum power for a half hour because of a very strong out going current and found my fuel guages had moved about the same amount as they do in nearly a day of normal cruising. If the curve is correct it should have burned as much in a half hour as it would in 8 hours of normal cruising. I would say it is pretty close to reality. This is with a clean bottom and clean props. With a dirty bottom and contaminated props it would take a lot more fuel to maintain the 80% cruising RPM.
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Old 01-03-2011, 09:58   #4
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Re: Okay, it Was All My Fault . . .

Yup, my Cummins engines came with fuel meters integrated to the GPS that tells me burn rate and miles per gallon in real time. The last 80% and up drops the mileage significantly.

For my engines, as low as 0.8 miles per gallon.
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Old 01-03-2011, 10:07   #5
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Re: Okay, it Was All My Fault . . .

Lannen: I just installed same engine, haven't been able to check fuel consusumption yet. If you don't mind, what was your RPM, LWL, boat weight for that 1/2 gph consumption at 5 kts. Also, what is your WOT RPM 3000, 3200, ?
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Old 01-03-2011, 10:09   #6
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Re: Okay, it Was All My Fault . . .

Quote:
Originally Posted by David M View Post
Yup, my Cummins engines came with fuel meters integrated to the GPS that tells me burn rate and miles per gallon in real time. The last 80% and up drops the mileage significantly.

For my engines, as low as 0.8 miles per gallon.
Now that would be handy, unlike my fuel gauge which at the first sign of heel or chop declares I've used half my fuel and won't tell me the truth until I'm anchored again.
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Old 01-03-2011, 10:18   #7
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Re: Okay, it Was All My Fault . . .

Running out of fuel is like running aground. We all do it sooner or later. Much harder to do either a second time as you are more aware. Bypassing the elecronics I still use an old yard stick dropped in the tank to see how much fuel is left and calculate time and distance. Hasn't failed me yet.
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Old 01-03-2011, 12:51   #8
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Re: Okay, it Was All My Fault . . .

Quote:
Originally Posted by chris07732 View Post
Lannen: I just installed same engine, haven't been able to check fuel consusumption yet. If you don't mind, what was your RPM, LWL, boat weight for that 1/2 gph consumption at 5 kts. Also, what is your WOT RPM 3000, 3200, ?
Wow... tough questions- I've only had the boat 10 years and this engine for 3. Now, ask me about rum consumption~

I run at around 1600-1700 RPM because of the TFAR factor. (That Feels About Right) Stick the tank (no fuel gauge installed) and when I'm a bit below half I top up. Count the gallons and divide by engine hours. I come up with just short of 1/2 GPH average.

40' boat, WL something shorter than that, weighs around 25,000 lbs. I've had the engine up to 2900 RPM for very short periods. I'm only at 2200-2500 RPM to make it to the draw bridge on time when I need it.

My fuel generally celebrates birthdays...
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Old 01-03-2011, 13:25   #9
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Re: Okay, it Was All My Fault . . .

Good story. Thanks
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Old 01-03-2011, 13:39   #10
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Re: Okay, it Was All My Fault . . .

I met a sailor who called his engine "Jesus". When I asked why, he said "it died for my sins".
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Old 01-03-2011, 13:42   #11
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Re: Okay, it Was All My Fault . . .

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Originally Posted by lannen View Post
I've seen where I can buy a fancy meter thingy to hook up to my Garmin chart plotter that will monitor fuel flow and tell me what I already know for free...
If you mean the Garmin one I think, last time I looked, it needs a minimum of 2GPH to read. I suppose it isn't for us.
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Old 01-03-2011, 14:35   #12
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Re: Okay, it Was All My Fault . . .

Just what is this "crusing rpm" I'm always reading about so I can know when I'm at 80%?

My engine says 3600 rpm max and 3000 rpm continous. I know from the past (because I ran out of fuel) that if I run around 2400-2600 rpm and do about 6 knots I use about 1.25 gals/hr. But if I run about 2000 rpm at 5 knots I burn about .8 gal/hr. It's also easy to tell by ear alone that the engine is more comfortable at the 2000 rpm.

If I look in my Yanmar manual it suggests from the curves that the best efficiency (for the engine, which isn't the same as for the boat as a whole) would be around 2600-2800 rpm.

Just what is the "cruising" rpm?
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Old 01-03-2011, 16:58   #13
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Re: Okay, it Was All My Fault . . .

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I met a sailor who called his engine "Jesus". When I asked why, he said "it died for my sins".
To good!
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Old 01-03-2011, 18:14   #14
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Re: Okay, it Was All My Fault . . .

Thanks, I like your approach to life
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Old 02-03-2011, 21:00   #15
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Re: Okay, it Was All My Fault . . .

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Just what is this "crusing rpm" I'm always reading about so I can know when I'm at 80%?

My engine says 3600 rpm max and 3000 rpm continous. I know from the past (because I ran out of fuel) that if I run around 2400-2600 rpm and do about 6 knots I use about 1.25 gals/hr. But if I run about 2000 rpm at 5 knots I burn about .8 gal/hr. It's also easy to tell by ear alone that the engine is more comfortable at the 2000 rpm.

If I look in my Yanmar manual it suggests from the curves that the best efficiency (for the engine, which isn't the same as for the boat as a whole) would be around 2600-2800 rpm.

Just what is the "cruising" rpm?
I think you already found it !
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