what i need to know is what reduction in weight could I
get by using kelvar or carbon fibre. I am looking for something that can be
loaded on the roof of an european car by one person easily. one of the lads

You can get a good reduction simply by using foam stiffeners in the hull and
making it thinner. You can also use epoxy resin and forgo gelcoat for
painting. Study the making of canoe molds before you "leap" as (IIRC) they
need to flex for easier removal depending on the actual canoe design.. I
wouldn't use carbon fiber except maybe in a race canoe but kevlar is nice in
canoes. I have 2 of kevlar..
Greg Sefton