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Old 10-03-2018, 03:46 PM   #1
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Affordable fuel usage meter

I would love to advance past the measured sight glass and guesstimate method to work out our fuel burn but am not prepared to spend $1000 to do it as once I have the numbers I would not use it again.
But I would spend $100

After my success getting a $20 engine water/oil temp alarm on eBay I thought I would try the same for fuel and found these.

This one has 1/2inch fittings rated for diesel for $70




This one has 1/2inch fittings rated for diesel for $55



I would need one on the low pressure side of fuel to engine
And one on the fuel return to tank.
Both easily accessible and fitted on ours.

At start of run set both to zero
Run for an hour at 1000rpm
Subtract one reading from the other and that's usage at that speed

Repeat for 1050, 1100, 1150 etc

Thoughts?
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Old 10-03-2018, 04:05 PM   #2
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Should work out. THere may be a bit less accuracy than the dedicated units
[Floscans or Maretrons] built for the purpose but those should come up with reasonable results.

Just have a look at the specs for each units accuracy AND for the flow rate. If the flow is not towards the middle of the meter capacity then accuracy will fall off.
For your purposes that may not matter a lot but I would still check so you know.
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Old 10-03-2018, 04:08 PM   #3
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Greetings,
Mr. 60. Great idea and in theory, it should work. The $75 unit appears to need two small batteries. IF the $55 unit does not need said batteries, I'd go with it. I have had several "devices" ruined due to battery leakage over the years. You know, those flashlights that seldom get used and subsequently forgotten about...


The only variable I can think of would be the condition of your bottom. Fuel usage will vary with amount of fouling.



That being said, IF you already know how much fuel is returned to your tanks (engine manual information perhaps?) when running, you could get by with one although I don't know if the amount returned is a linear or logarithmic function or if it depends on the make and model of one's engines....
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Old 10-03-2018, 04:11 PM   #4
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One question: Are you sure you want to add one of these to your fuel line not knowing if you can trust these considering it can compromise your ability to run your engine? I would thin twice before taking the risk to be without propulsion in the middle of nowhere.
I would at least plan to have a bypass so I can run even if something goes wrong.

L
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Old 10-03-2018, 05:02 PM   #5
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Quote:
Originally Posted by Lou_tribal View Post
One question: Are you sure you want to add one of these to your fuel line not knowing if you can trust these considering it can compromise your ability to run your engine? I would thin twice before taking the risk to be without propulsion in the middle of nowhere.
I would at least plan to have a bypass so I can run even if something goes wrong.

L
Can you trust anything these days?

Could have spent a lot more and bought floscan and got problems
Floscan problems

And eventually ended up with this.
FloScan Australia| Fuel Flow Professionals | Sydney, NSW

Quote:
. FLOSCAN CLOSURE
It is with deep regret that I must inform you that after 40 years Floscan Instrument Company has closed the doors of its Seattle factory. At this stage product and spare parts are not available.
I have been advised there are plans to reopen in approx 6 months under new ownership.
Over the last 20 years I have been responsible for Australian Sales and Technical support for the Floscan range of fuel flow meters.
I still have a lot to give and would very much like to hear from any prospective employers.
I'd rather take it in the shorts for $100 than $1000
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Old 10-03-2018, 05:20 PM   #6
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What I meant is that this introducing a potential source of big headache for little value.
I thought about it also found all the component to get a flow meter on the cheap side, then thought a bit more about that and decided that my wish to know exactly how much fuel I burn does not worth the risk of being stuck cause things went wrong.
Just another point of failure along the line.

L
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Old 10-03-2018, 05:25 PM   #7
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Quote:
Originally Posted by C lectric View Post
.

Just have a look at the specs for each units accuracy AND for the flow rate. If the flow is not towards the middle of the meter capacity then accuracy will fall off.
For your purposes that may not matter a lot but I would still check so you know.
Specs as follows for the $55 one


Flow speed range : 0-10LPM
Total flow number: 1-999999 L
White background light LCD
Flow sensor connecting type: G 1/2''
Power input: 12-24Vdc
Accuracy: 0.5%
k parameter= 6.3
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Old 10-03-2018, 05:31 PM   #8
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Did Floscan start back up again? I'd heard they were closed, but didn't hear they were planning to re-open.

Frankly I don't see myself buying their gear unless they move the decimal point to the left at least one digit on the price. With two diesels, I'd need four sensors, plus the computer to connect them all to, plus the NMEA interface. Much as I'd love to see accurate fuel burn numbers in real time, I don't need it THAT badly!
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Old 10-03-2018, 05:34 PM   #9
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Originally Posted by Lou_tribal View Post
What I meant is that this introducing a potential source of big headache for little value.
If doing looong passages which is our intention, there is a lot of value in finding the optimal sweet spot and shaving several litres/ hour off of fuel burn.
Could add thousands of miles to range and save thousands of dollars.

This comment by delfin in another post made me want to get the real numbers
Quote:
. with 2450 gallons of fuel, my range is around 4500 miles at 8 knots and 7000 miles at 6.8 knots
Big difference
Quote:
I thought about it also found all the component to get a flow meter on the cheap side, then thought a bit more about that and decided that my wish to know exactly how much fuel I burn does not worth the risk of being stuck cause things went wrong.
Just another point of failure along the line.
Agreed and I do love simplicity myself.
Reality is before we head off on these looong passages we would keep it in for a season where we are now doing short hops and gathering data with clean bum and dirty bum through various rpm and conditions.

Once we have those numbers it'll come out and revert back to what we had.
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Old 10-03-2018, 05:44 PM   #10
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I am a little puzzled. Looks like you have a million dollar yacht and want to put a cheap Chinese flow meter on it?


Seriously, even if it does work what are you trying to accomplish? Look at your engine's prop curves. That will tell you within 10%, probably as good as those meters, how much fuel you are burning.


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Old 10-03-2018, 05:56 PM   #11
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RT, you seem obsessed by bottoms. Maybe you should apply for the Supreme Court?

Waste of money and effort. Full tanks, Hobbs meter time noted, go boating, note Hobbs meter and fill up. Ergo bingo, fuel consumed/time. The rest is ocd.
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Old 10-03-2018, 06:12 PM   #12
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I am a little puzzled. Looks like you have a million dollar yacht
Looks can be deceiving
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Old 10-03-2018, 06:14 PM   #13
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Waste of money and effort. Full tanks, Hobbs meter time noted, go boating, note Hobbs meter and fill up. Ergo bingo, fuel consumed/time. The rest is ocd.
That will tell me fuel burn
What it won't do is tell me fuel burn at 1000rpm vs 1500rpm and all points in between

That plus to fill the tanks just for that exercise will cost $11500 and take a couple of years at current usage rate.
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Old 10-03-2018, 06:48 PM   #14
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Quote:
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That will tell me fuel burn
What it won't do is tell me fuel burn at 1000rpm vs 1500rpm and all points in between

That plus to fill the tanks just for that exercise will cost $11500 and take a couple of years at current usage rate.
But doing exactly that is how you calibrate the device.
Thinking out of the box, you could calibrate with a pair of outboard fuel tanks.
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Old 10-03-2018, 06:51 PM   #15
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One of the things to understand with these type of flow meters is that they are usually accurate within a range, not from 0 to a large flow rate. Flow scan was very emphatic about using the appropriate flow meter for the expected cruise fuel burn. They basically told me that the flow meters for my 450 HP motor with flow rates in excess of 20 GPH would be inaccurate for my 135 HP motor with expected flow rates between 2 and 6 GPH.

Before investing a lot of energy in this project, I would want to check the accuracy of both units though the expected range. This will take some doing as they maybe accurate within a narrow band.

Ted
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Old 10-03-2018, 06:58 PM   #16
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Greetings,
Mr. 60. If you simply wish to establish a benchmark under various conditions and engine speeds, how about a graduated tank (40 or 50 liters marked in 1 liter increments perhaps?)? Do a temporary installation incorporating your feed and return lines and use it as a sort of day tank to get your #'s then revert to original.
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Old 10-03-2018, 07:14 PM   #17
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Flowscan also required a pulsation dampener on the (return?) fuel line to stabilize the erratic output caused by the fuel pump. I would maybe disconnect the return line & watch the flow to see if it was steady. That could have an effect your calculations.
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Old 10-03-2018, 07:35 PM   #18
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. They basically told me that the flow meters for my 450 HP motor with flow rates in excess of 20 GPH would be inaccurate for my 135 HP motor with expected flow rates between 2 and 6 GPH.
Interesting
I got my initial 1250rpm fuel burn guestimates from a mate who has a larger, heavier, beamier but less windage boat with the same engine and he was using floscan.

My initial observations at the time using 500 litres in, marking sight tube and burning it at 1250 showed similar numbers but now a couple of years down the track I'm not so sure.

Now I reckon 1150 rpm gives closer to the fuel burn he claims to be getting and the prop curve chart would suggest same.
Boat speed down by less than 1 knot but going by the prop curve probably 8 litres an hour better off.
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Old 10-03-2018, 07:38 PM   #19
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Originally Posted by djmarchand View Post


Look at your engine's prop curves. That will tell you within 10%, probably as good as those meters, how much fuel you are burning.


David
Thanks.
Just downloaded the prop curve and it was quite revealing.
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Old 10-04-2018, 12:53 PM   #20
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I wonder if there's any interest in an open-source flow monitoring solution?

I find it hard to believe that the component costs really justify the price of the systems available to the marine market. Surely in industry and other applications, flows are measured at far less expense.
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