Cheap fuel flow meter

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R_p_ryan

Senior Member
Joined
Dec 11, 2014
Messages
171
Location
USA
Vessel Name
Shellbourne
Vessel Make
1978 Mainship 34 Perkins T6.354
This is less than $20 and I'm wondering if it would be safe to install: 13mm Liquid Fuel Oil Flow Meter Counter diesel gasoline Gear flow sensor 3 12V -in Flow Meters from Industry & Business on Aliexpress.com | Alibaba Group.

I'm thinking I'd need two - on for for the feed and the other for the return. The meter would be before the filter so if it fell apart it would't reach the engine. I'm also wondering if it should be on a bypass line, so I could choose for fuel to either flow through the meter or around it (in case it became clogged).

The proper marine gear is over $500, and I think fuel flow would only be interesting at first, since I'd get a sense of the flow rate by RPM pretty quickly and stop consulting the meter.

Would this be a hazard onboard?

Thanks,
RR
 
It is not a complete meter. It is just a fuel flow pulse generator that produces a pulse for every .46 ml of fuel that passes through it.


To have a real meter you would need a microprocessor to count the input and return pulses, calculate the difference, convert to gph and then drive an appropriate display.


How accurate are they? I know what they say +/- 0.5%. But since you are dealing with the difference, a drift of a couple of percent can result in 10-20% change in the net fuel reading.


Might be fun to play with if you are a real electronics do it yourself geek. But not for me.


David
 
djmarchand said:
It is not a complete meter. It is just a fuel flow pulse generator that produces a pulse for every .46 ml of fuel that passes through it.


To have a real meter you would need a microprocessor to count the input and return pulses, calculate the difference, convert to gph and then drive an appropriate display.


How accurate are they? I know what they say +/- 0.5%. But since you are dealing with the difference, a drift of a couple of percent can result in 10-20% change in the net fuel reading.


Might be fun to play with if you are a real electronics do it yourself geek. But not for me.


David
Click to expand...

uh, yeah, I am DIY geek. I was thinking about hooking it up to my Arduino (microcontroller).

I'm just concerned about the materials used and if there's any risk of something dissolving in the diesel and harming the injector pump, etc. I have no clue what my fuel consumption is at various RPMS and I've considered the alternative, which is to put a small plastic fuel tank on a scale and weigh it before and after making some runs at various speeds. Seems like about as much effort as splicing in a couple of these sensors.
 
Do these devices take into account what gets returned to the tank? I suppose if you compare flow with flow at different speeds it is still a useful comparison, but I wondered.
 
R_p_ryan said:
uh, yeah, I am DIY geek. I was thinking about hooking it up to my Arduino (microcontroller).

I'm just concerned about the materials used and if there's any risk of something dissolving in the diesel and harming the injector pump, etc.QUOTE]

It says its used for fuel oil so it must be compatible. Put it ahead of the filter if you're in doubt.
Click to expand...
 
I had the same thought. Saw the same units and more on eBay. I agree with David though on the accuracy concerns, especially when there is a fuel temperature difference between the fuel supply and return lines. If you read up on the Maretron FFM100 they talk about some of these challenges. I came to the conclusion that cheap flowmeters and simple a-b calculations probably wouldn't give me any better data than I have already from Cummins and from people like Jay who have published detailed fuel consumption stats on sisterships.

I'd be interested in hearing how it goes if you do try this, and if you do how you'd verify and/or calibrate the results.
 
Not a fuel flow meter that would provide functional GPH readings at various RPMs...


But I think it's possible to at least address overall fuel consumption with more accurate fuel tank gauges. Using the CruzPro digital tank gauges -- which can be closely calibrated to tank capacity and can provide a read-out in gallons or liters -- it should be possible to simply do the math at the end of a cruising segment.


That of course depends on how accurate the senders can be, no matter what gauges are used for display; verdict is still out, there.


I'm gradually re-doing our instrumentation at the helm, and hope to get to the fuel gauges this coming Spring. The re-do wasn't originally intended to address fuel consumption info, but that may be a useful outcome.


-Chris
 
Actually, the CruzPro built-in alarms was a major driving feature for my plan...


That and that it's pretty much a drop-in installation: same hole size as what I've already got, easy wiring right at the helm (no cable pulls required), uses existing senders, etc.


-Chris
 
Jeff F said:
I had the same thought. Saw the same units and more on eBay. I agree with David though on the accuracy concerns, especially when there is a fuel temperature difference between the fuel supply and return lines. If you read up on the Maretron FFM100 they talk about some of these challenges. I came to the conclusion that cheap flowmeters and simple a-b calculations probably wouldn't give me any better data than I have already from Cummins and from people like Jay who have published detailed fuel consumption stats on sisterships.

I'd be interested in hearing how it goes if you do try this, and if you do how you'd verify and/or calibrate the results.
Click to expand...

Jeff,

I see we have the same vessel. My '78 has the '77 T6.354. You mentioned published stats on fuel consumption - do you have access to this information and could you forward to me?

Regarding the calibration, I suppose I could use a scale and weigh the fuel in a small, outboard motor style plastic tank. Then do an B-A calculation and compare with the "area under the curve" by tracking time and data points from the flowmeter.
 
R_p_ryan said:
Regarding the calibration, I suppose I could use a scale and weigh the fuel in a small, outboard motor style plastic tank. Then do an B-A calculation and compare with the "area under the curve" by tracking time and data points from the flowmeter.
Click to expand...

Or you could just run for "X" hours and divide into the fuel used. Bingo....Average GPH fuel use.

Some of you guys want to really complicate this!!!
 
R_p_ryan said:
Jeff,

I see we have the same vessel. My '78 has the '77 T6.354. You mentioned published stats on fuel consumption - do you have access to this information and could you forward to me?
Click to expand...

Here's a prop curve for the 165 hp 6.354 - very close to your engine. As discussed elsewhere, if you have the appropriate reduction gear/prop for your boat you can see fuel consumption and hp for a given RPM from this. I have a Cummins BT6. Lots of variables, but fun to explore.
 

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Very interesting! If I could only put out enough trim tab to get on plane at 2100 rpms it appears I'd be at ideal fuel/speed economy. (without over-propping of course).

Thanks,
Robert
 
Well, 2,100 may be ideal from a specific fuel consumption standpoint, ie lb/hp hr., but it won't be the best NM/gallon. There is no "best" NM/gallon point, only a speed that you are comfortable with that won't drain your tanks too fast.


Most trawler cruisers run at a speed to length ratio of from 1.0-1.3. That is 1.0 - 1.3*sqrt(lwl). For the Mainship 34, it is about 5.5-7.2 kts which should require 1.5-2.5 gph of diesel.


David
 
Right. For optimizing MPG slower is always better, because the HP/speed curve is not linear. Travel at 6 knots and your MPG will be more than double that at 12 knots, trim tabs or no.

Take your speed at various rpms and overlay it on the prop curve and this will become evident.
 
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I'm going to get flamed on this, but I have come to regard GPH as a useless number.

I understand that, before GPS, the best way to know your fuel consumption for a given trip was to calculate, in advance, what your GPH was at any given speed, then plug that into a normal time-speed-distance calculation. Simple and reliable. Since your GPH at a given STW ideally never changes, you could factor in set and drift of currents and winds, and do some highly accurate dead reckoning. I've been there, done that.

But, in the end, the number we really need is MPG. How far can I go before I have to fill up again? How much fuel can I save if I slow down to X knots? What will it cost me to speed up and get there sooner?

Granted, you can convert GPH to MPG pretty easily. But why bother? Once you've figured out the curves for your hull and engine(s), picked your sweet spots for where you like to run in different conditions, the number you actually use is MPG.

I'd also accept GPM - gallons per mile - or gallons per 100 miles, or per 10 miles, as an even better number to track. But most of us are more familiar with MPG so we stick to that.

I used to be ashamed of not knowing my GPH at any given engine RPM off-hand, and feel a little less "salty" when I talked about MPG instead. But I'm no longer apologetic about starting with the number I actually care about, rather than having to derive it each time.

This is the 21st century. We have better information now.

Some traditions are OK to let go of.
 
No flaming here.....because it is simple math most of the time....you only need some of the variables to figure out the rest easily. So where you start is purely personal choice.

For my current style of cruising...NJ to FL and back once a year.....I don't really care about much other than the engine starts, runs OK till I shut it down and do I have enough fuel till I WANT to refuel (as opposed to NEED to refuel).

I don't even plot the courses anymore on the plotter to get an accurate ETA. With the miles out of a guidebook, in 5 seconds I can figure a pretty accurate ETA in my head.

I look ahead for adverse currents in known bad spots...and plan from there...

Otherwise...with a 6-6.5 know boat that throws little wake.....turn her on, set the throttle and wait the pre-requisite 5-10 hours till I get where I want to be. Not much I can do to change much.

BUT....I know about and have run boats with all sorts of options.

So depending on who you are and what boat you have...like me...I have little to offer others other than ..."do what the **** you want and enjoy":D

I do see fuel monitoring as more of a maintenance tool than planning...but they are great for the first couple of trips in a boat till you get to know her.
 
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CaptTom said:
I'm going to get flamed on this, but I have come to regard GPH as a useless number.

I understand that, before GPS, the best way to know your fuel consumption for a given trip was to calculate, in advance, what your GPH was at any given speed, then plug that into a normal time-speed-distance calculation. Simple and reliable. Since your GPH at a given STW ideally never changes, you could factor in set and drift of currents and winds, and do some highly accurate dead reckoning. I've been there, done that.
Click to expand...

No flame here. I did some RPM/speed tests, converted outcomes to NMPGs, and calculated our "nominal" fuel consumption... enough to know as RPMs rise, so does fuel use. (Duh!) That -- and some general idea at a couple planing RPMs -- was pretty much all I really wanted to know. And we're fairly cavalier about trip planning; we get there when we get there.

FWIW, I do see actual speed changes at any given RPM, caused by differences in tides, currents, wind, etc... and that indicates GPH likely is changing at various points along a trip. That's not enough difference to raise a blip on my radar...

-Chris
 
I agree. All I care about is mpg. But how do we get that in the absence of accurate expensive fuel flow meters? That's how the thread started. Seems to me that the way to get there is to understand fuel consumption along the prop curve, then match to measured speed of the boat for a given hp/fuel input to create a chart that shows mpg by rpm. Once I've done that I won't care about gph. It's just an input into the final set of calculations.

I'm sure this has been done before, but I'm new to this and it's winter :)
 
or cruise and write down the miles covered and fuel bought.

doesn't work as well for all boats initially...but after awhile, even simplistic data becomes useful to the point that the other details are just fluff.

say you cruise 2000 miles a year...plus or minus....

after 5-10 years of doing it and the average trip costs XXX in fuel.....and not being able to change much...isn't that average number good enough?

not for stretching a tank to the next fill up...but for many...that doesn't matter....so when is data too much?

only personal preference matters there.....
 
If I had a FD boat I'd agree. Determining an appropriate cruising speed is relatively easy, and there's not a big difference between fast and slow cruise. But with a SD hull like my Mainship 34 there is a much wider range of cruising speeds available. The PO of my boat chose to cruise at 8-9 knots. Other owners cruise at 6-7 knots, and some who have repowered are cruising at 12-14 knots. That's a big spread, and my goal is to fully understand the choices WRT fuel consumption and use that information to influence my choices. I'm a data guy, if that's not clear by now :)
 
Unlike car manufacturer's one company makes the engine and another installs it in their boat. We think in gallons per hour first because that is what the engine manufacturer's publish. They don't know what kind of boat their engine is in. A 200 hp engine could be in a 40,000 lb trawler that uses 1/4 of that typically or in a 6,000 lb go fast boat that uses 80% of it typically.

It is up to us to convert the numbers that the engine manufacturer's publish in their prop curves to NM/gal based on how fast and at what rpms our boat can go.

Also there is no EPA mpg testing and reporting requirements for boats.

OTOH, Mainship did pretty good job, while they were in business, of letting each engine manufacturer test their boat/engine and report fuel consumption vs rpm and MPG. They were always a little on the high side of speed and MPG because the weight was minimal, but if you adjusted for that, they were pretty good.

David
 
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