Help calculate fuel tank capacity

[phstol]

There are so many variables in the fuel usage /gph/mile of a sailboat that it doesn't make much sense, IMO, to sweat the calculation of the last drop of the tank's capacity.
(The other dimension to your question is how accurately if at all, you will measure the last gallons in the tank above the pickup pipe while under weigh. I would be interested in your comments on that).
From a practical standpoint, you would get close enough by using simple trigonometric calculations: Taking the dimensional diagrams that you have created, and use a ruler and square to reduce the main body of the tank to a cubic polygon when viewed from top and all sides. Calculate its volume V=LxHxW.
Now you are left with one or more prism shaped bodies. Reduce each to a right angled prism and apply V=1/2 Basex H x Depth.
For any remaining pieces you can continue this process, or ignore , or eyeball estimate.
If you really want to be anal about it, you can build a polystyrene model and measure that out to your heart's content....
Don't forget to subtract a few gallons to allow for the hight of the pickup point, and to check that the floor of the tank is level to the waterline of the boat.
Fair winds...

[Brewgyver]

Originally Posted by Cool Hand Luke

I would venture you definitely have LESS than 219 gallons:

Not sure where you went wrong, but your calculated volume is WAY off.

EVEN IF the tank was constructed as a regularly shaped rectangular object with parallel top and bottom, front and back and left and right sides, using ONLY the longer dimensions, and without clipped corners, the dimensions would be 52 Long, 31.54 Wide and 18.5 High, right? For a volume of 30,341.48 c.i., or 131.35 gallons.

[Cadence]

Originally Posted by Brewgyver

Did I miss something? When did the OP say anything about rust?

I think he only asked if the broker was blowing smoke at 100gal.. The consensus of opinion is it is pretty close.
How do people read things into it?

[Cool Hand Luke]

Originally Posted by Brewgyver

Not sure where you went wrong, but your calculated volume is WAY off.

EVEN IF the tank was constructed as a regularly shaped rectangular object with parallel top and bottom, front and back and left and right sides, using ONLY the longer dimensions, and without clipped corners, the dimensions would be 52 Long, 31.54 Wide and 18.5 High, right? For a volume of 30,341.48 c.i., or 131.35 gallons.

You're absolutely right... I used the width twice instead of width and height. Ugh, I'm an idiot

[Brewgyver]

Originally Posted by Cool Hand Luke

You're absolutely right... I used the width twice instead of width and height. Ugh, I'm an idiot

Yeah, when I took your product and divided by the length and height, it was obvious.

Meaning it was obvious that you used the 52" dimension twice, not that you're an idiot!
Can't tell you how many time's I've carefully measured, laid out, calculated, then cut wrong!

[captwylie]

7.48 gallons per cubic foot, 1728 cubic inches to a cubic foot.
I calculate 122.2 gallons minus 8% for expansion I would say 110 gallons