You can build the hull of a canoe, rowing boat or sailing boat in less than a day using Plastazote, a closed cell foam similar to that used in camping mats.
Plastazote is tough, does not absorb water and can be welded (and repaired) with a hot air gun or heated knife. Since Plastazote was developed as a high-performance closed-cell foam, other competitors, mainly Chinese, have entered the market - see Alibaba for examples.
This is an ideal project for individuals or family groups that want a light robust recreational boat that is easy to car top and is completely unsinkable.
It might also be of interest to youth groups to make and sell them as an enterprise project.
For more details of this project - and to obtain copies of instructions, contact [email protected]