Thanks Ramona, great tip! I am now proud owner of 2 windsurf sails with carbon fibre masts. Free!
I am thinking of using one mast and sail as the main. I could then use the second mast to make a boom and maybe the second sail to make a jib later. But I have a million questions if you guys don't mind.....
Is the size and shape of the windsurf sail suitable for this application? I would use a wooden dowel inside the carbon fibre mast to attach the mast to the boat. Would the mast be strong enough without forestay and shrouds? (see, I have done some reading

)
With the boom attached to the bottom of the sail it would not be horizontal. Does this matter? As an advantage the tack could be lower and I would still have some headroom at the end of the boom.
Is the sail likely to move with the boom when tacking or would the luff being sleeved over the mast not allow this?
I would like to hear your opinions!
Cheers,
S