Just curious

Anyhow, getting away from the subject of foam flotation, I am toying with using 2 liter bottles for light weight, redundancy, cost, and ease on construction. I have to fill two long seat cavities. I calculate I need about 1800 lbs (28 cu.ft.) of positive flotation. Styrofoam appears to cost about $4.00 per cubic ft. However, 2 liter bottles cost 8 cents if you buy them from the redemption people.
Approximating a liter to be the same as a quart, each bottle will weigh half of a gallon's weight, or 4.17 lbs. I need 1800 lbs of flotation, so I need 1800/4.17 or 431 bottles.
The bottles cost 8 cents so my cost is $34.48. The foam would have cost me about $114.00.
Which is better? This seems to be a good question since I don't have to carve the foam, use glue, spend hours fitting blocks into irregular cavities.
Instead, I keep jamming bottles into the cavities until they don't shift when I screw down the seat tops.
Will they ever leak? Probably not even if the boat was weighted down and submerged for years. Maybe a couple could leak.
However, they will not ever take on moisture---- even if a bunch are sitting in water a lot of the time.
Plastic lasts forever, or almost, if kept in the dark. Actually, they say 450 years in the ground. Probably the same for styrene foam. The issue, of course, is whether they will remain bouyant while a boat recovers from a spill, and continue to be ready for a spill many years hence. That's all I care about. And just think, I can replace the bottles one day a couple of dacades from now, and still I will not be spending nearly as much as I would for styrene foam, and styrene foam is probably a lot cheaper than foams that don't eventually absorb water.

 

One liter is .26 gallons Alan. So, 2.17 pounds per one liter bottle, less the weight of the bottle(s) of course.

 

Read it again. Also, the bottle's weight is cancelled out at least by the difference between a quart and a liter ---- 1.0566:1.
Had I converted liters to quarts exactly and then subtracted bottle weight, the number of two liter bottles would have decreased slightly anyway. The point I was making didn't require absolute exactness. Only enough accuracy to make the argument.