is the idea that once the foam is wet it will be less heavy becaused there is less foam do to the bottles?
thats one of the reasons yes!
here is my reasoning for the plastic bottles-
1 - a little bit less weight (i understand perfectly dry its negligible)
2 - use less foam (cheaper)
3 - more bouyant in case i sink it for whatever reason it will float higher.
4 - WHEN (not if) water gets in the gunwhales after refoaming, it is impossible for it to hold AS much water as before since the bottles are sealed.
5 - when i meet a hot green peace chick on the beach that is bitching about my evil 2 stroke i can tell her that i built it using recycled plastic bottles and then she will want to come home with me...