Cheap Gas Gauge

W

Wayne McCown

New member
This one is free!

Before flling up with gas, I put a pencil line at the gas line on one of the plastic see-through gas tanks. Then I put in exactly five gallons of gas and stopped pumping, climbed into the boat and and put another pencil mark at the top of the gas line.

When I got home, I measured the distance between the two pencil marks. Then, beginning from the bottom of the tank and working up, I made pencil lines on both tanks at that measured distance: at 5, 10, 15 and 20 gals.

I had some 1/4" black striping at hand (it costs me a couple of buscks at some point, but at the moment was free!). So I cut 3" lengths of this tape and stuck it on each of my pencil marks. Now, I can easily look at the gas tanks and estimate quite accurately how much I have in each tank!
 
Somebody already knows this I'm sure, but I don't. :oops: Are those tank walls perpendicular to the bottom, thus making the distance a 5 gallon fill covers, the same at the bottom of the tank as at the top? If the tank walls at the outboard ends are sloped out as they rise from the cockpit sole,(matching the hull wall), then the measurement will change, decreasing as it gets closer to the top. I know there are some of you who know the shape of the tank, and some who could figure the volume even if it is sloped, so come on now and chime in here, and thank you.

Harvey
 
There is also the problem that if the temperature of the fuel changes up or down the level will change also. That is why gasoline pumps at the station are temperature compensated.
 
Reply to Harvey:

I had to remove and empty my gas tanks last summer. Yes, the walls are perpendicular. The top, however, slants towards the back of the transom.

Having filled the tanks from completely empty to completely full took exactly 22 gallons last summer. The measurement method I shared looks to fit that number: the last two gallons are "squeezed in" (in the slanted area) above the 20 gal. mark.

This "cheap" gas guage, of course, does not compensate for gas expansion and shrinkage!
 
Calculating gas volumes in an irregularly shaped tank reminds me of my old calculus classes. If you have an equation for the shape of the sides you can rotate this equation around the vertical center axis, and then calculate the rate of change of volume with depth; i.e. you are calculating the rate of change of a solid geometry object as a function of distance from the bottom. Of course, this assumes that the shape is symmetrical around the vertical center axis. If not, the calculations become even more difficult.

Ouch! My brain hurts just thinking about it . . . :crook I like the black tape solution better!

Also, as B~C points out, a 'cheap-gas' gauge would be better than a cheap 'gas-gauge'!

iggy
 
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