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Old 02-02-2014, 09:11 AM   #1
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Those damn fuel gauges

We all know how inaccurate fuel gauges are on boats. Is there an accurate way to tell how much fuel is in the tank? I have 2 wing tanks that are slightly elevated and I am unable to access the top to dip them. (I used to do this on my last boat and never was in doubt about fuel level). I've tried the tap method but really can't be sure. Any suggestions?
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Old 02-02-2014, 09:29 AM   #2
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We all know how inaccurate fuel gauges are on boats. Is there an accurate way to tell how much fuel is in the tank? I have 2 wing tanks that are slightly elevated and I am unable to access the top to dip them. (I used to do this on my last boat and never was in doubt about fuel level). I've tried the tap method but really can't be sure. Any suggestions?
I suggest searching in archives via "search" button in this page's top bar. Many informative threads/posts exist.

Best Luck1 - Art
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Old 02-02-2014, 09:44 AM   #3
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Originally Posted by knotheadcharters View Post
We all know how inaccurate fuel gauges are on boats. Is there an accurate way to tell how much fuel is in the tank? I have 2 wing tanks that are slightly elevated and I am unable to access the top to dip them. (I used to do this on my last boat and never was in doubt about fuel level). I've tried the tap method but really can't be sure. Any suggestions?

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Old 02-02-2014, 09:45 AM   #4
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I have one of these installed. It is amazingly accurate.

http://www.cruzpro.com/fu60.html

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Old 02-02-2014, 09:49 AM   #5
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I don't need Flowscans I know my fuel burn, I just want to know how much diesel is in the tank. I don't trust that flowscans are anymore accurate from some things I've read.(garbage in garbage out, it is only as accurate as the calibration) The best way would be sight gage on the tank but alas not installed.

Art I'll search

I guess what I mean is I like to see how much fuel I have, not let some gauge guess. My tanks are slightly oval and I know how to calculate volume so for me I like it simple and mechanical not more electrical gadgets.
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Old 02-02-2014, 09:53 AM   #6
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You say you are going to keep the boat a long time in another thread...I would work towards some kind of sight gauge if possible....but that's up to the tanks and install configuration.

Are your tanks top or bottom feed?

Also the "stick" method doesn't require a solid object. On several USCG cutters I deployed on...they "stabbed" the tanks with a windup measuring tape and a plum bob on the end. Still not always convenient but thinking out of the box for some.
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Old 02-02-2014, 09:57 AM   #7
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Top feed and only have a coupe of inches of clearance above the tank. Flex tape would work. I'll have to look into it and see if I have an access point like my old boat.
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Old 02-02-2014, 10:20 AM   #8
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You say you are going to keep the boat a long time in another thread...I would work towards some kind of sight gauge if possible....but that's up to the tanks and install configuration.

Are your tanks top or bottom feed?

Also the "stick" method doesn't require a solid object. On several USCG cutters I deployed on...they "stabbed" the tanks with a windup measuring tape and a plum bob on the end. Still not always convenient but thinking out of the box for some.
Perfect! You took the words right out of my...well fingers
Done and used both, and both are simple, easy, and effective!

We used the sight gauges on the airboats. Work perfectly. (Just saw your response. Disregard the sight gauge idea.)
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Old 02-02-2014, 10:21 AM   #9
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Originally Posted by psneeld View Post
You say you are going to keep the boat a long time in another thread...I would work towards some kind of sight gauge if possible....but that's up to the tanks and install configuration.

Are your tanks top or bottom feed?

Also the "stick" method doesn't require a solid object. On several USCG cutters I deployed on...they "stabbed" the tanks with a windup measuring tape and a plum bob on the end. Still not always convenient but thinking out of the box for some.
ps - GOOD Fn' idea... Duhhh... I could a had a V8!!! TY for sharing that little piece of CG genious!

I also like/trust direct stick fluid readings better than any other means. My tanks both have too much turn in filler hose from deck mount to tank... so that even a 3/8" dowel can't enter. NOW, thanks to your post, I'm gonna try rigging a fabric tape with svelt and non edged (so it can'y get hung up inside on anything in tank) plumb bob weight-end and try my luck!

Bravo - Dude!!
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Old 02-02-2014, 10:40 AM   #10
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Head pressure gauges are very accurate. Might be tuff to install on top of the tank if you have limited access. But, they dont neccessarily have to be installed in the tank. Anywhere you can get to the bottom (drain plug maybe) to put the pressure line will work. A gauge and small air pump to purge the line and "walla" you have a tank level gauge. You just need to know how tall the tank is and convert the static head to percentage or gallons. Simple and works everytime. I think Tank Tender sells the complete setup, or you can do it yourself.
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Old 02-02-2014, 11:19 AM   #11
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I'm new at this, so take the following with a grain of salt.

(We have sight gauges, but fuel docks are far apart here, the remote ones often run out of fuel, and inlets can be very long and infrequently visited.)

I kept track of fuel added over seven months, and hours on the engine. With those known variables, and the total volume in the tanks, gives me a pretty good indication of fuel useage over time.

The PO added a 40 gallon tank, so that gives us 140 gallons in three tanks. We burned on average 1.5 gallons per hour over those seven months.

140 (gallons) divided by 1.5 (gallons per hour) = 93 (total hours running time).

93 (hours) minus 1/3 (reserve in tanks) = 60 (hours running time).

60 (hours) x 6 (consevative knots estimate) = 360 miles.

Ballpark figures for sure, subject to refinement with more experience!
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Old 02-02-2014, 11:39 AM   #12
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We all know how inaccurate fuel gauges are on boats.
My fuel gage is extremely accurate. So were the gages on my previous boat.
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Old 02-02-2014, 12:47 PM   #13
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You do have a fuel shutoff on the tank? Close it, take off the fuel hose and attach a tee, put a valve on the vertical outlet, reattach the fuel line, add a clear hose et voila, sight gauge. Doesn't have to be "on" the tank and should be shut off unless you are looking at it. The other end goes back to the tank or tee it to your overboard vent.

My sight tube is mounted next to the trim around the door to the engine room which is very convenient to monitor, but the valve isn't. I only need to monitor one of the two tanks.
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Old 02-02-2014, 01:54 PM   #14
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Originally Posted by Art View Post
My tanks both have too much turn in filler hose from deck mount to tank... so that even a 3/8" dowel can't enter. NOW, thanks to your post, I'm gonna try rigging a fabric tape with svelt and non edged (so it can'y get hung up inside on anything in tank) plumb bob weight-end and try my luck!:
I had the same thing. PO used a length of regular 12-2 house wire. Just flexible enough to get around the bends, but still stiff.

I found a better way. Still in the electrical department at Home Depot, a steel "fish" tape used for fishing wires through walls.


Cost around 10 bucks. I scuffed it up with a wire brush so the fuel would stick better, and notched it every inch from the bottom. Not perfect, but it's the best solution I've found yet. I plan to order a couple of floscans when a few other budget items are behind me.
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Old 02-02-2014, 04:35 PM   #15
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I had the same thing. PO used a length of regular 12-2 house wire. Just flexible enough to get around the bends, but still stiff.

I found a better way. Still in the electrical department at Home Depot, a steel "fish" tape used for fishing wires through walls.


Cost around 10 bucks. I scuffed it up with a wire brush so the fuel would stick better, and notched it every inch from the bottom. Not perfect, but it's the best solution I've found yet. I plan to order a couple of floscans when a few other budget items are behind me.
TY CaptTom! I'll look at that. Figure I can take length of stainless wire, rough it up for depth of tank, spray paint flat black with white paint stripes at 1/8 intervals to full... and give her a try! Be easy to store as straight rod next to bridge seats; weathering would me no prob!. I'll post once accomplished. By george - This should work!

Happy Boating Daze - Art

PS: I have Flow Scan for duals... waiting for me to install - maybe this spring/summer... I'm in no rush!
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Old 02-02-2014, 04:56 PM   #16
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FYI--About 100 years ago I worked as captain of the last WW II era built PT boat still in service. PT 728 did history tours with paying passengers out of Key West. Her two main fuel tanks were mounted just forward of the engine room bulkhead and on either side of the vessel. The filler pipes made 90-degree bends between the deck plates and the top of the tanks. Even so, our technique was to jiggle an ordinary metal tape measure down through the filler pipes until it contacted the bottom of the tank. We had a table which gave us fuel remaining based on the number of inches of the tape that were wet by fuel. Foolproof, but oftentimes quite frustrating to get that tape to negotiate the 90-degree bends. The other captain of the boat had the magic touch, and could get an accurate reading first try. I was not so lucky, but eventually developed a workable technique. Good luck!
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Old 02-02-2014, 04:57 PM   #17
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My fuel gauge.




100 percent accurate, 1 inch is 4 gallons, 18 inches is full. Each tank is the same (3 tanks)

I have two back-ups and a folding one for when I feel exotic and fancy. I am such a high roller.
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Old 02-02-2014, 10:22 PM   #18
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@SCOTTEDAVIS a 1/4" dowel rod wastes less fuel. :P Not as accurate though. The multiple use of things on board factor is way up.
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Old 02-02-2014, 10:29 PM   #19
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@SCOTTEDAVIS a 1/4" dowel rod wastes less fuel. :P Not as accurate though. The multiple use of things on board factor is way up.

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Old 02-02-2014, 11:07 PM   #20
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FloScan was the right answer. The unit has a reset able totalizer that will count your fuel consumption from the time it was last reset. If you know how much you started with, you will always know how much is left. I used this method for many years as a backup to my fuel gauge. Fill it up, reset the totalizer count to zero, and add up the gallons until they match what you can hold, and you are now out of fuel!
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