BigBendFishing.Net

Bman, the link to the calculator you used doesn't work for me. And I can't reproduce the numbers you came up with.

Here's what I came up with:

A cubic foot of water weighs 62.4 pounds. An object lighter than water will support, or float the amount of water it displaces less the weight of the object.

The formula for the area of a circle is pi times the radius squared.

We are looking for the volume of a 10 foot length of 4 inch pipe. This first tells me we're working with different units of measure. Lets get the units of measure to feet. The radius of a 4" pipe is 2". That converts to 0.166666 of a foot. That number squared is 0.0277777.

Pi is roughly 3.1416
3.1416 x 0.0277777 = 0.087266 square feet.
The pipe is 10 feet long.
0.087266 x 10 = 0.87266 cubic feet of volume in a 10 foot length of 4 inch pipe.
0.87266 x 62.4 (weight of a cubic foot of water) = 54.45 pounds.
I have no idea how much a 10 foot length of 4 inch PVC, 2 caps, and the hardware to mount it weighs. But you have to subtract the weight of that stuff. Lets say all that stuff weighs around 5 pounds. That tells me your 2 pipes will support around 50 pounds each, or a total of 100 pounds.

I'm not always the best at math. anyone is more than welcome to explain where I went wrong.

EDIT:

I also ran the numbers for a 6 inch pipe. A 10 foot length of 6 inch pipe would provide 122.52 pounds of buoyancy, less the weight of the pipe and brackets. You could probably gain 200 pounds of buoyancy using 2 six inch pipes.

You would be better gluing these things the kids use to float the rivers called "noddles" on the side of a john boat, at least it's own weight wouldn't destroy the integrety of the hull.

Maybe someone has a big ol truck tire inner tube you could 5200 around the whole boat. Kinda like a Zodiac.
By the way, TC is correct that a cubic foot of air will support approximately 62 lbs. in fresh water at sea level.