How to calibrate and label a sight gauge on a new tank.

[Dougcole]

Hi All,

I am having a sight gauge installed on my new fuel tank, but the tank fabricator does not calibrate or label the tank in any way. I'm going to fill the tank from a fuel truck that I use frequently, he said he will pump in 25 gallons at a time so I can mark the tank. I'm thinking lines with a sharpie to start, but I would like to go with something longer lasting and better looking. Maybe a label maker (I have one) but I am not sure if they will adhere well to aluminum. Any other ideas?

Thanks,
Doug

 

[tiltrider1]

I used a sharpie 10 years ago. Made a mark on the tube and the number every 25 gallons. Still my go to gauge. I also put masking tape behind the sight tube and marked a line every 5 gallons. Once in a while I use this instead of the sharpie mark right on the sight tube. I tend to use this only when I am trying to top off the tank without spilling.

 

[Marco Flamingo]

Use white duct tape or masking tape on the tank behind the sight glass. If the bottom of the tank is sloped, mark that in couple of increments and then only a few when the tank is a regular shape the rest of the way full. No point continuing to mark if every additional 20 gallons continues to be the same increment because the tank shape is uniform. Then you have time to figure out what you want as a permanent solution after the tank truck is gone. Another nice number to have calculated is something like "inch per hour" of cruise time. It can make the calculation of "how many days till refuel" easier.

 

[mvweebles]

How big are your tanks and where is the sight tube located? My sight tubes are located at the aft end of the tanks (225g/ea.....i think) which was a mistake on my part. Trim really affects the reading. Not much I can do but just wanted to to set expectations that getting an accurate reading is sometimes easier said than done. Like so many things on a boat, plan on paper is defeated by reality.

Hope your outcome is better than mine

Peter

 

[Dougcole]

My tank is 150 gallons, I'm putting the tube on the side of the tank near the forward end. The bottom of the tank is flat, then slants up to the edge. Pic of the old tank is below, the new tank is the same size and shape. The gauge will be on the section that is on top in the below pic

 

[mvweebles]

My tank is 150 gallons, I'm putting the tube on the side of the tank near the forward end. The bottom of the tank is flat, then slants up to the edge. Pic of the old tank is below, the new tank is the same size and shape. The gauge will be on the section that is on top in the below pic View attachment 163351

If you have a choice, put it in the middle.

Peter

 

[Dougcole]

Unfortunately, if I put it in the middle I will not be able to easily see it as it would be behind the engine.

 

[Portage_Bay]

You can get very close with a bit of middle school geometry. It looks like your tanks don't taper fore and aft, only on the ends which are trapezoids. Calculate the area of one end. If you don't want to do the arithmetic here's an online calculator Area of a trapezoid. Next the volume of the tank is the area of the trapezoid times the length of the tank. You phone probably has a calculator to convert cubic volume to liquid volume. If not Google will find one for you.

Select an interval you like. Maybe 1". "H" will increment by 1". "A" will be constant. There will be a new "B" at each increment of "H". You can spend far too much time on your knees measuring "B" at each increment. Or simply the original "A", "B" and "H" the draw it up in CAD or on graph paper. You don't need to calculate each increment, do every other one and average between. Cross check with your fuel vendor's offer to pump 25 gallons at a time.

I did my tanks that way and am very happy with the accuracy. Don't forget you are measuring the outside of the tank so be sure to subtract the tank wall thickness.

Mvweebles is correct, the sight glass belongs in the middle of the tank fore and aft. Mine are on the ends to I have to estimate a correction for trim.

 

[Uisce Beo]

As far the sight gauge hard to see behind the engine, etc can I just suggest having an accurate gage is more important than having a convenient one. You’re not going to use it/look at it all that often but if it’s not accurate you’re going to be forever second guessing yourself.
Ask me how I know!
I basically have a fuel guage that tells me I have 1) a lot of fuel, 2) some fuel or 3) not much! It is a constant irritation to me.

 

[Comodave]

I would do some temporary marks on the tank. Then make a template of the marks and go to a sign shop. Have them make the permanent markings out of something like nametag plastic. Then glue the plastic to the tank next to the sight gauge. Do something with clear contrast like white and black. You will enjoy the really nice permanent markings over time.

 

[jleonard]

If you know the tank capacity, which is easy to figure, all you need are 1/4,1/2,3/4, and full markings. You can interpolate the rest easily.
Thats all I had and I could accurately predict how much fuel i could take on. And that was with a swing arm gage on only one of the saddlebag tanks.

 

[Dougcole]

The tank is built at this point and ready to go into the boat this morning, the gauge is on the forward end, there is no moving it. That said, the tanks sits pretty flat and the fwd end, if anything may be a little on the high side meaning that it may under read how much fuel is in the tank. I’m ok with that as it creates a bit of a fudge factor.

 

[Pascall]

I used a label maker to indicate the diesel quantity.
This has been on it for 20 years with no problems.