Fuel flow gauge - any pointers for a raggie please?

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West Coast

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Hi all, apologies for the raggie type question, but thought I might find some words of wisdom in this part of the forum!

I have a 44’ jeanneau sailboat with a 54hp yanmar engine, with a 200 litre tank. Engine fuel consumption is relatively small, perhaps between 3 - 5.5 litres per hour depending on revs. My boat has a factory fitted fuel level gauge which is inaccurate and unreliable, and I have no other way of knowing how much fuel I have in the tank. I am currently recording engine hours and revs, which gives a reasonable estimate of usage but as a raggie, my engine can be on/off when passage making depending on wind etc. So recording hours and revs is cumbersome and I don’t always remember.

So - options could be a new fuel gauge but am worried about sealing holes in the moulded plastic diesel tank. Another option could be to fit a fuel flow gauge (sensor on the flow and return, with box to calculate nett usage) but an advised that these may not be very accurate for such a relatively small fuel consumption.

Grateful for any advice on best way forward!
 
Floscan is the best I have seen costs over £1k.

The problem is measuring flow and return lines and reaching net fuel use.

Is the tank rectangular with a flat base? If so perhaps if there is a cap you can use make up a dip stick in wood that is calibrated and dip the tank when in port on the level so to speak. Or if you can see a side or tank end and if the tank is see through, empty tank and fill 10 or 20 litres at a time and mark on tank level with a felt pen and keep two spare jerry cans as reserve.
 
Hi, tank is opaque, so cannot see through it unfortunately. A dipstick approach would be good, but the tank is under the aft cabin berth so not practical to easily access. The fuel filler pipe arrangement won’t allow me to dip fro the fuel filler point either :(
 
Bandit said:
Floscan is the best I have seen costs over £1k.

The problem is measuring flow and return lines and reaching net fuel use.

Is the tank rectangular with a flat base? If so perhaps if there is a cap you can use make up a dip stick in wood that is calibrated and dip the tank when in port on the level so to speak. Or if you can see a side or tank end and if the tank is see through, empty tank and fill 10 or 20 litres at a time and mark on tank level with a felt pen and keep two spare jerry cans as reserve.
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Floscan has ended production. There are quite accurate fuel level sensors and gauges available so a new one may be your best option. Sealing shouldn't be a problem as long as you take care not to damage the plastic.
 
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On cars fuel flow and MPG is not calculated using fuel at all. It's calculated on air flow into the engine thus removing the need to measure returning fuel.
 
I have Tank Tender on my boat , the third boat I have fitted them to.

Accurate to a cm, fit and fill the tank 10l at a time and record reading then draw a graph.
 
Sailorsam101 said:
On cars fuel flow and MPG is not calculated using fuel at all. It's calculated on air flow into the engine thus removing the need to measure returning fuel.
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That isn't correct. It is calculated (rather than measured) from the fuel injector open instructions given by the ECU (on both petrol and diesel cars) and is pretty accurate.

To OP, floscan was always the inferior choice and hard to calibrate. The best generally available kit is Maretron and they have sensors suitable for your HP. I use them on my generators which are around 45HP. They measure flow and return, with temperature compensation, and the black box calculates the net and produces n2k data that you can display on your plotter screen and/or another display. Very good indeed and factory calibrated. Easy to fit with npt fittings. Because your plotter also knows your speed, the system can display instantaneous litres per mile, which is very useful when you're trying to minimise fuel consumption on passage

http://www.cactusnav.com/maretron-f...MI4eL2nJG63AIVUoCRCh1-Fwr4EAQYAyABEgLct_D_BwE
https://www.maretron.com/products/ffm100.php (and click on "accessories" tab for the flow sensors)
https://www.panbo.com/maretron-ffm100-fuel-flow-monitor-test-part-1-as-good-as-it-gets/
 
Thanks all for comments and links. The Maretron looks like good kit, but at a price! I guess you get what you pay for.

If I was to revisit the fuel level gauge, any recommendations as to types or makes to consider or avoid?

Cheers
 
Sight glass

Fit a cock and push valve connected to a vertical pipe up the side of the tank .
Either
1- Tee into the existing OUT line if at the bottom
2- make a hole and plumb in ( after suitable draining of course )
£50 tops jobs done .

There’s nothing more reassuring than MK1 eyeball the fuel level (s) .
I have gauges about s as accurate as everyone else’s — er useless well not far off .
We also have fuel consumption deltas in L/ H on our engine monitor systems .

But there’s nowt better than actually seeing the levels before a unfamiliar passage or during .
 
Portofino said:
Sight glass

Fit a cock and push valve connected to a vertical pipe up the side of the tank .
Either
1- Tee into the existing OUT line if at the bottom
2- make a hole and plumb in ( after suitable draining of course )
£50 tops jobs done .

There’s nothing more reassuring than MK1 eyeball the fuel level (s) .
I have gauges about s as accurate as everyone else’s — er useless well not far off .
We also have fuel consumption deltas in L/ H on our engine monitor systems .

But there’s nowt better than actually seeing the levels before a unfamiliar passage or during .
Click to expand...

On light aircraft we work out the hourly fuel consumption at different rev settings because the fuel guages are notoriously inaccurate: before the first flight of the day it's complusory to look into the tanks to visually check the levels.

If I had a motor yacht I would fit a small day tank to monitor the fuel consumption every few hours: no expensive sensors To go wrong and the reassurance of actually seeing the remaining fuel available. Guessing you'll use about 40hp at max continuous cruise so 2g/hr and a 20 gall tank fitted with t-pieces into the fuel lines would suffice .
 
rustybarge said:
On light aircraft we work out the hourly fuel consumption at different rev settings because the fuel guages are notoriously inaccurate: before the first flight of the day it's complusory to look into the tanks to visually check the levels .
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So, a thought - if I could automate a log of engine time and revs, I could keep an accurate record of fuel used? Ie an automated version of what I have been doing manually to date? This could be done by tapping into the Rev counter output from the alternator which drives the Rev counter, and a simple computer setup?
 
West Coast said:
So, a thought - if I could automate a log of engine time and revs, I could keep an accurate record of fuel used? Ie an automated version of what I have been doing manually to date? This could be done by tapping into the Rev counter output from the alternator which drives the Rev counter, and a simple computer setup?
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That sounds like a very sensible solution, but getting actuate data of your actual fuel consumption is going to be difficult with a big tank of diesel to measure.

I'd tap into the supply and return fuel line with a simple t-piece and on/off valve, then set up a seperate temporary graduated container to accurately measure your consumption at different rev settings.

You can then draw a reference graph which will tell you how many hours running time you have left in your tank: your gps will give you accurate​ sog info to your next waypoint ...
Sorted !
 
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I have already begun to build a data base of consumption info, recording Engine time and revs and using published consumption data to estimate fuel used. Then refilled the tank and compared estimated usage to actual. Have done this 3 times so far this season with 200 litre tank, refining the estimates each time, so now have reasonably close numbers of usage gains revs. I can keep refining this data with an automated log system, updating a consumption lookup table as I go.
 
West Coast said:
I have already begun to build a data base of consumption info, recording Engine time and revs and using published consumption data to estimate fuel used. Then refilled the tank and compared estimated usage to actual. Have done this 3 times so far this season with 200 litre tank, refining the estimates each time, so now have reasonably close numbers of usage gains revs. I can keep refining this data with an automated log system, updating a consumption lookup table as I go.
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I'd recommend using fuel consumption rather than revs as your reference numbers. Eg on a 50hp engine set your consumption to 10ltr/hr (probably about 2500revs) which is dead easy to divide into your tank capacity to give hours left at those settings.

Every day will give different sog numbers dependant on conditions, so a simple gps will give you an exact time to your next waypoint.

A cheap calculator or even a pencil & a piece of paper will give you very exact results once you've nailed down the actual fuel consumption.:)
 
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Fuel consumption has no relevance on SOG.

What I've done on boats before is to fill it up to the top and then go for a motor for three hours at cruise rpm..forgetting about what speed i am doing.

Then come back and fill up to the same point again...hey presto you have you fuel burn at a know RPM.
 
Sailorsam101 said:
Fuel consumption has no relevance on SOG.

What I've done on boats before is to fill it up to the top and then go for a motor for three hours at cruise rpm..forgetting about what speed i am doing.

Then come back and fill up to the same point again...hey presto you have you fuel burn at a know RPM.
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Imo fuel consumption is the most vital element in the sog calculation because it directly influences range.
 
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