: I have glassed the outside of my hull and it now curls and uncurls with
: either change in temperature or humidity - not sure which. What is the
: best way of ensuring that the moment I glass the inside the shape is the
: design shape and not either a banana or an arrow?!

all the other ideas are good - spreaders,on forms etc.

i have had a related problem with building outside. haven't done it, but one idea i have contemplated is semi-sealing the bottom opening of the kayak with taped plastic 4 or 6 mil sheet in order to slow down the change in air temp and humidity. with care, i also think one could set up a string of low wattage light bulbs inside in order to keep the air warmish at a more constant temperature. it is certainly one way to control(reduce) your adjacent humidity while attempting shape changes to make your more narrow yak.

and (hehehe) why such a huge wide yak at 430mm??(17"!!) set those light bulbs to burn and get that rocket down to 400!(15.75")