Determining capacity of a tank

[ted655]

:confused: I want to know how many gallons of diesel my tank holds.
The formula I have says L" X W" X H"= cu. in., divided by 231.
When I apply this to known capacities of tanks in a catalog, I don't come close. Even allowing for strap indents & room for vapor expansion I'm always "almost" twice their ammouint.
Anyone have a method of doing this , using simple math?
Thanks:)

[lazeyjack]

lx hxw, in metres,
say .6x.6x.6= .216 cu/m obviosly is 216 litres
or in feet, 2x2x2 =8 cu ft
6.25 gals in cu feet, =48 plus,
are you pulling our legs?

[lazeyjack]

oh and that is imp gals, you will need to x .8 for US gals

[charmc]

Ted,

For me it's simpler to work from cubic feet. 1 cu ft = 7.48 US gal. 1728 cu inches = 1 cu ft.

So a tank 12" W x 24" H x 48" L = 13,824 cu inches, divided by 1728 = 8 cu ft, x 7.48 = 59.84 US gal. "max" capacity. 13,824 divided by 231 = 59.84, same answer.

Working, or usable capacity can be as low as 70% of total volume, since there needs to be vapor headspace and the fuel suction tube is off the bottom of the tank. A conservative marine tank supplier will factor in an allowance for the suction tube's being fully submerged even during pitch and roll movements, so working capacity will always be significantly less than total volume.

[alan white]

Inches high times inches wide times inches deep, divide that by 1728, you get cubic feet.
One cubic foot of water weighs 62 lbs. One pound of water is a pint, eight pints to a gallon, 62 divided by 8 makes 7 3/4.
7 3/4 gallons to the cubic foot.

[alan white]

And Charlie's gotten to it while I was writing. He had the actual weight of water, a bit less than 62 lbs per cubic foot.

[alan white]

:confused: I want to know how many gallons of diesel my tank holds.
The formula I have says L" X W" X H"= cu. in., divided by 231.
When I apply this to known capacities of tanks in a catalog, I don't come close. Even allowing for strap indents & room for vapor expansion I'm always "almost" twice their ammouint.
Anyone have a method of doing this , using simple math?
Thanks:)

I divided 1728 by 231, your figure, and got 7.48. So the figure gives the weight of one gallon. Read the formula again, I like that 231 figure, easy to remember.

[alan white]

yeah--- okay. You take the cubic inches, divide by 231, and you get the weight if water, not the gallonage.

[charmc]

:confused: Hey Alan, I was working strictly with volume. 7.48 US gallons of water at "standard" temp will fill 1 cubic foot volume.

One gallon of water = 8.33 pounds (I know, Stu, it's easier in metric :) ) and 7.48 gallons x 8.33 pounds = 62 pounds.

Same, same, but I figured volume. My point is that working capacity will be less than volume.

My head hurts. G'night all. :)

[ted655]

Yes, I was serious, even if it is fall off the log for you :) .
Thanks, I have more than 1 way now. Here is a sample of what I encountered'
Sold as a 29 gal tank. 25.75 X 23 X 8 = 4738 cu. in. / 231 = 20.51 gal. (not close enough for me), where's the other 9+ gals?
14.5 X 14 X 23 = 4669 / 231 = 20.21 gal. (sold as 12 gal tank) again a 8+ difference, this time the other way. Here is another conversion that isn't close either.
To Convert Multiply by To Obtain
cu.in. ------- 0.00433 .---------- gal.
Any how, thanks to all, I'll be able to figure my tanks now, so I know how much $$$ to borrow to fill them. $3.48 gal. on the Ohio river as of yesterday, ouch!!:mad:

[alan white]

:confused: Hey Alan, I was working strictly with volume. 7.48 US gallons of water at "standard" temp will fill 1 cubic foot volume.

One gallon of water = 8.33 pounds (I know, Stu, it's easier in metric :) ) and 7.48 gallons x 8.33 pounds = 62 pounds.

Same, same, but I figured volume. My point is that working capacity will be less than volume.

My head hurts. G'night all. :)

You can tell I'm not much of a mathematition. Obviously, 16 fluid ounces doesn't weigh quite 16 oz either, and a gallon doesn't weigh 8 lbs. exactly.
And therein lies the rub--- I'll use 8.33 from now on.

[Poida]

X + Y = Z

Where:
X = Syphon out existing fuel
Y = Filling up at Gas Station
Z = Amount indicated on bowser

What a genius

poida

[Raggi_Thor]

I am glad we converted to the SI a hundred years ago, or so :)

[lazeyjack]

Yes, I was serious, even if it is fall off the log for you :) .
Thanks, I have more than 1 way now. Here is a sample of what I encountered'
Sold as a 29 gal tank. 25.75 X 23 X 8 = 4738 cu. in. / 231 = 20.51 gal. (not close enough for me), where's the other 9+ gals?
14.5 X 14 X 23 = 4669 / 231 = 20.21 gal. (sold as 12 gal tank) again a 8+ difference, this time the other way. Here is another conversion that isn't close either.
To Convert Multiply by To Obtain
cu.in. ------- 0.00433 .---------- gal.
Any how, thanks to all, I'll be able to figure my tanks now, so I know how much $$$ to borrow to fill them. $3.48 gal. on the Ohio river as of yesterday, ouch!!:mad:

sorry ted, look mate try workin litres, 1000 l in a cu /m
its so simple, get a tape measure, measure it in mm, 100mm, = tenth of metre and so on. so 100 =.1m, .2 m =200mm, so its easy

.5x .7x.3 the result=litres 105
3.8 l in one usa gal
dont worry I,m absolutely useless at cad , but can do math , simple in my head, I also have many woman and boats in my head too:))

[ted655]

X + Y = Z

Where:
X = Syphon out existing fuel
Y = Filling up at Gas Station
Z = Amount indicated on bowser

What a genius

poida
.
So simple a xaveman thought of it.:D

[alan white]

My "favorite" use of the inch system is building stairs, where odd spaces get divided into whole numbers of treads and risers. Like 12' 11 1/4" divided by 14. Has to be done decimally, then converted back to fractions. That is when I envy the rest of the world.
I've heard that old Swedish carpenters still use the "Thum" (? spelling), or thumb, which is, I think, an inch. Raggi might know about that. Inches are actually convenient at times.

[charmc]

I also have many woman and boats in my head too:))

Me too! That's not a problem! :) :)

[Harold McNett]

L X H X W / 231 will give you the number of gallons. The Dims that are given in the catalog, is the space the tank will take up.

[ted655]

L X H X W / 231 will give you the number of gallons. The Dims that are given in the catalog, is the space the tank will take up.
.
:confused: ????? Huh? That's what a dimension is, "space occupied".
A tank that measures L X W X H, should hold the gallons responding to the math of it's dimensions. This is, within reason of course, the thickness of the tank material, strap indentations, neck fills, vapor space etc., will alter the pure math. BUT.... the demos I posted are 8+ gallons off! 1, too little & #2, too much. 8 gal, off is not acceptable in my book.:rolleyes:

[Harold McNett]

does this tank in question have handles? fill cap above the tank? You are correct 8 gallons is too much difference, if you are dealing with a 20 gallon tank. At the same time it does not take all that much area to use up 8 gallons. Ex: a tank that is 1 foot by 1 foot by 1 foot will hold 7-1/2 gallons.

[ted655]

These tanks are permanent mount boat fuel tanks. 1 is a below deck model, the other is a on exposed mount tank. The catalog is "Overton". I just picked it up and used those tanks as a model to test the formula. When they (I computed several more, none made sense), came out so far off the stated gallons, it made me doubt the math. So, I came here. The math is correct, so what are we buying?
No handles or other unusual construction, just plain plastic tanks. I could even understand if the applied math always fell on one side of advertised capacity, but one tank is too much, another too little. It's crazy.
I have other catalogs, maybe I'll try the math on them tonight & see how they fair.

[Guillermo]

Just an stupid question: are those tanks parallelepipedic of square or rectangular section, or not?

[Harold McNett]

It does make one wonder if honesty is still something we take with pride or is it something that we fudge on when it comes to our benifit. I'm at a lost on why there is so much difference between what is stated and what you get. If you get it figured out as why it is, I would like to know also.

[ted655]

Just an stupid question: are those tanks parallelepipedic of square or rectangular section, or not?
.
:confused: "Parae.....?? My ignorance is revealed I guess. A tank that is 14.5" X 8" X 24" is a rectangle (I think).
All I was doing was checking my math skills. What better way than to compare to a known quanity? Thanks to ya'll, I know the method is NOT the problem. Thanks.
.
Those with interest in these "advertised" tanks can get a catalog & pick a size. I've checked 8 sizes & none of them come close. I'm thinking that hand filling each with a gallon container is the only syre way to know the truth.

[Poida]

You don't need to fill them Ted.

Put a dipstick in the tank, mark where the fuel goes to, put in a gallon, make a new mark where the fuel is then.

The difference between the marks is a gallon.

Measure the distance, assume 1 3/16" then mark the stick every 1 3/16" from the bottom.

The mark at the top of the tank is the total gallons.

Also to calculate how much is in your tank you are going to need a dipstick anyway so you kill two birds with one stone.

Poida

[ted655]

My last post was largely sarcasim. I now have faith in the math and less in the integrity of catalogs. Thanks to all.