Is it a 100% fiberglass windsurfer mast, or does it have carbon in it too? If it's 100% fiberglass, it may be a total piece of crap (or it could be half decent, but it will be pretty heavy). If it's got carbon in it (50% or more would be real good), it's probably stronger than the old aluminum pole - there's a reason that aluminum windsurfing masts are not made out of aluminum any more.

There may be a sticker at the base of the mast which tells you the carbon %, or if the mast is black, that's usually a pretty good indicator.

sm