Sad that they put all this foam (sponge) in boats these days.

[Gone Fishin']

Saw a pic years ago where a guy used plastic quart oil bottles all put neatly in his before he reinstalled the floor. Should certainly float and last a long while.

I have always thought that plastic bottles would do good for flotation. Not the crushable water bottles. More of the heavier duty ones like with gatorade, powerade, etc. They are usually built stout and a little hard to puncture. I would think if you were to glue the lids on tight and stack them into areas as tightly as possible that it would work good.

It would take a long time for them to probably degrade, they should hold air perfectly and there is nothing for the water to soak into. I should just run between them and out the area. Only thing I could think of is the possibility of expansion and contraction in hot/cold weather. Might affect the bottle some or the area if packed too tightly causing some distortion. Or could rattle around some if not packed somewhat tight. But for aluminum boats I think this would be acceptable.

Now I have not tried it or currently know anyone that has, but in theory it should work great.