use lighter foam…
12 to 15 kg density at about 55mm for the finished core thickness
put on perimeter stringer with 15 to 20mm wide pvc
overlap the pvc skins over the perimeter stringer
the pvc should be around 60 to 80kg density and the lowver density skins are better if you go to 5mm on the deck
use 2 to 3oz glass and epoxy resin to adhere the skins to the core
you must use a vacuum bag to put the skins on for about 8 hours perferably longer if you have cold environment
if the temperature is under 25 degree celcious maybe 24 hours for a reliable cure
after the skins are on, finish shape the rails and glass the board with 6 oz
lap the bottom glass around to the deck and let the deck glass hang
use pvc inserts around the fins boxes
the finished board weight will be around 12 pounds
use and epoxy fill coat and a polyester finish coat
if you want the board really strong use a lightweight wood like paulownia, balsa or cedar
cedar and paulownia will be more durable and a bit heavier
balsa will make the lightest strongest board for its weight but if balsa gets wet it gets soggy
the board will require a vent
if you make the board to stiff and limit it range of movement it will snap easily
stiff does not mean strong in a surfboard
its not a load bearing wall, it is a dynamic flexible panel
carbon is no good
this is a correct schedual for a performance longboard and will yeild a very durable and light surfboard
center stringer do not have any meaning in this construction and will ruin the board
cedar skins at about 3mm thick will make the stongest lightweight board possible
incidentaly mike sabin said to me (he builds big yachts) that without heat curing it is best to leave epoxy clamped for 3 days
3 days
this is the man that built an open 40 and sailed it around the world with 2 little kids, has built many sandwich boards and is a factory floor manager of a large yacht manufacturer… when replacing mast spars whilst sailing around the world . he told me they would break again if they were not clamped and cured for 3 days… when your life depends on it