Hi John,
In Oz we have been using sailboard masts, aluminium and carbon for a couple of years on our Mosquitos as Spinnaker poles both have been excelent for the job very light and strong, with small tip diameter [low windage] being another advantage. Don't know of anybody using a standard windsurfer mast though, being a old sailboarder racer I had bits of aluminium mast in the shed to experiment with.
Straight aluminium tubing is used on most other cats with spin. I have seen, but usualy more like 50mm with a thin wall.
We have some great detail and pitures of spin. setup on our Mosquito website.
http://home.vicnet.net.au/~mosquito/sp_rigging.htm Regards Gary.