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Old 10-05-2018, 06:32 AM   #21
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The speed at which you choose to cruse will be the biggest determinant of fuel burn .

Once you decide on a set speed the RPM will need to be reduces as you burn fuel and use stores.

The SQ RT of the LWL in Knots is a good place to start looking for lowest fuel consumption..

Then during a crossing keep a "how goes it" , logging fuel consumes vs distance traveled.

If you get 1/2 way across and have only used 1/4 of your fuel , you can increase the speed with the only harm to your wallet.
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Old 10-05-2018, 08:13 AM   #22
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I think there's way too much talk about "gallons per hour" in the boating world.

I suspect it's a holdover from the pre-electronic days when all you had access to was RPMs, no accurate speed indication.

Today, it's very easy to calculate MPG, which is really all you care about. Better still, calculate gallons per 100 miles, an even easier number to work with.

In the end, whether you start with GPH or MPG, to do any realistic voyage planning, you must convert it to the number of gallons it'll take to go a certain distance.

Why not start with that number?
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Old 10-05-2018, 10:59 AM   #23
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This one is $40 on ebay. They're cheap enough, you could buy spares.
https://www.ebay.com/itm/LCD-Liquid-...UAAOSwxOVbrtkA
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Flow Meter.jpg  
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Old 10-05-2018, 06:14 PM   #24
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Originally Posted by Lepke View Post
This one is $40 on ebay. They're cheap enough, you could buy spares.
That would work. Of course, you'd need two for each motor. And a bit of a manual effort to subtract return flow from supply flow. And And also convert liters to gallons (for those of us in the backward US of A.)

I see the sending units (and others like them) are stamped with a mL per pulse value. Presumably all you'd need is a computer to count pulses, do the math, and output the real-time GPH used. In NMEA format, of course.

Could be fun. All this process control stuff is new to me; I was in the business side of IT. No doubt there are far smarter people than I, who've done this sort of thing before. Presumably it wouldn't be too hard for them.

Have I piqued anyone's interest yet?
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Old 10-05-2018, 09:26 PM   #25
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This is something I plan to try, seems reasonable priced haven’t heard any real time reviews yet.

Interactio | Optio Fuel Flow Monitor


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Old 10-06-2018, 05:38 AM   #26
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Assuming identical twin engines really only one pair is needed....same engines with same props at same rpm's should be near enough and likely within accuracy tolerance of the meters
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Old 10-06-2018, 07:44 AM   #27
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Originally Posted by ronbo404 View Post
This is something I plan to try, seems reasonable priced haven’t heard any real time reviews yet.

Interactio | Optio Fuel Flow Monitor
Wow. $1600 for a twin diesel setup. Not sure that's in the "affordable" camp, but it looks like a great system!

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Assuming identical twin engines really only one pair is needed....same engines with same props at same rpm's should be near enough and likely within accuracy tolerance of the meters
Interesting point. I can't disagree, but the geek in me says it would be a very unsatisfying solution.
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Old 10-06-2018, 07:49 AM   #28
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It is expensive but not as price as the flow scans were.

Fyi, those prices are Canadian dollars
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Old 10-06-2018, 10:18 AM   #29
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All of the flow meters shown in this thread have just one sensor. Diesels need two which was mentioned briefly a few posts back. You need one to measure total diesel flow and subtract the return diesel flow from another to get diesel burned by the engine.


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Old 10-06-2018, 11:53 AM   #30
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My solution is time.......Fuel used, and hours run. Over a 4 year period I have an excellent reference of Average fuel used per hour. I don't need any more than that along with some very accurate analog gauges on the top of my tanks... Cost is $00
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Old 10-06-2018, 12:33 PM   #31
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Originally Posted by djmarchand View Post
All of the flow meters shown in this thread have just one sensor. Diesels need two which was mentioned briefly a few posts back. You need one to measure total diesel flow and subtract the return diesel flow from another to get diesel burned by the engine.


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I didn't see the sense in posting two of the same picture but I did say two would be needed.
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Old 10-06-2018, 12:33 PM   #32
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My solution is time.......Fuel used, and hours run. Over a 4 year period I have an excellent reference of Average fuel used per hour.
Average fuel burn is relatively pointless for passage making where there will be 1000s of miles between reliable fuel sources.
I want to know what range I can get at 6.5 knots vs 7.5 vs 8.5 vs 9.5 knots.
12 litres/ hour vs 35 litres/hour
The difference in range will be 1000's of miles

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I don't need any more than that along with some very accurate analog gauges on the top of my tanks... Cost is $00
Your cost could well be many hours cruising at an inefficient speed
Probably doesn't matter if you don't do many miles away from a fuel dock and have cheap diesel
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Old 10-06-2018, 12:58 PM   #33
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I look at fuel monitoring systems more than just gph or fuel used. We have a FlowScan system and during the fuel tank replacement/engine room rebuild, one of the sensors was damaged so the system wasn’t working. While breaking in the rebuild, we had a fuel leak in the return line at an injector and came close to damaging the rebuilt engine. If the FlowScan had been working, it would have helped us find the problem sooner. The system has also given us an indication of how clean the bottom and or running gear is.
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Old 10-06-2018, 03:16 PM   #34
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Geeezz, I thought I was OCD, (BTW, that should be CDO so the letters are in the proper alphabetical order.) but all I do is watch the fuel gauge and get fuel when I need it......AND I DONT run faster than 7 knots. I know my range and I dont exceed it.


Kind of like my car. Do you worry about the gallons per hour on your car???? You instinctively know that if you go fast the fuel will go fast, if you go slow, you can drive further, and you watch the gauge. Simple.
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Old 10-06-2018, 05:10 PM   #35
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Geeezz, I thought I was OCD, (BTW, that should be CDO so the letters are in the proper alphabetical order.) but all I do is watch the fuel gauge and get fuel when I need it......AND I DONT run faster than 7 knots. I know my range and I dont exceed it..
Great for you.
As yet we haven't filled our 2000 gallon tanks and ran them down to see what we can get.
We can theorize, we can guess, but are not sure.
When we find out we will know and won't have a use for fuel usage meters any longer

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Kind of like my car. Do you worry about the gallons per hour on your car???? You instinctively know that if you go fast the fuel will go fast, if you go slow, you can drive further, and you watch the gauge. Simple
You are right, it is simple in a car.
For most of your driving you are close to petrol stations and if you run out its no drama as you simply pull to the side of the road and wait for someone to turn up with some more or a tow.

Different story to if we are on passage with several thousand miles between fuel stops and no one to bail you out.
Then you might be a bit more concerned about your sweet spot for mpg, especially when our fuel costs almost 2x what you pay.
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Old 10-06-2018, 08:02 PM   #36
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Cant compare to a car...no set and drift varying your speed/distance over ground per fuel use.

Accurate fuel consumption numbers allow you to close in on a reserve that is viable, not some guess.

Sure you can live without accurate numbers.... like you can without all kinds of safety equipment...till that one time, for whatever reason, it comes in handy.

I spent a career betting my life on accurate fuel numbers...as the tech got better...I could relax a bit more and more.

For a few dollars, I would love to have pretty accurate fuel info.....but because my boating doesnt require accurate numbers very often, a high price tag is what is stopping me from adding a system.
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Old 10-06-2018, 08:05 PM   #37
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It looks like you are going to tap into the fuel lines to add these meters. I wonder if you could just use a 5 gallon bucket with the return running back to the bucket and a known quantity of fuel, say 1 or 2 gallons, marked on the bucket. After you time the net burn off of a couple of gallons at various power settings, put everything back the way it was.

I noted when I fueled my boat for the 1st time that my tanks hold 12 gallons per inch on the sight gauges until I get to the last 50 gallons where the tanks taper and hold 6 gallons per inch. If you calibrated your sight gauges at your next refueling I think you could reach a confidence level equivalent to these gauges of unknown accuracy.

BTW, my engines (1983 Lehmans) burn very close to the fuel flows in the manual. So considering that I only cruise at 7 knots, and therefore am highly vulnerable to tides and currents, I wouldn't plan a voyage with less than a 25-30% reserve. This inclination on my part to hold a large reserve makes it unnecessary to have a super accurate fuel flow estimate.

But it sounds like a fun project.
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Old 10-06-2018, 08:11 PM   #38
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From what i understand Cummins pt fuel system shifts a lot of fuel.
Your 5 gallon bucket would be drained and the return overflowing very fast.

Tapping into the fuel line and returning it to standard is pretty simple.
Less effort than dicking around with extra small tanks and buckets IMHO.
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Old 10-06-2018, 08:32 PM   #39
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My estimates on fuel consumption over time are as accurate as flow meters. However it need to have accurate sight tubes and it's not instantaneous.
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Old 10-06-2018, 08:49 PM   #40
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I mistaken myself and reading posts now understand the goal of what Simi want to achieve. If I was to prepare a long range crossing I would do the same in order to get measurement as accurate as possible. Also I guess that it is easier to get measurement of a 200 gal tank than of a 2k gal tank, at least you don't need to burn 500 gal to get a reading

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