Welcome to the board Gerard. Being "in between jobs" is the ideal time to get another board, especially with summer coming on.
Windsurfer one designs come up on ebay and gumtree every few weeks, probably 2/3 of them are the pre-1988 (?) style with the non rotating centreboard. There was an almost identical Bombora produced board that was a copy of the one design- they also appear periodically. I am fairly certain the bombora ones had a fully retracting allgier type daggerboard and a US fin box. Theoretically this would allow an even higher level of high wind performance with a big fin and fully retracted centreboard compared to the one design.
The rotating centreboard is definitely the way to go. The other big difference between the pre-88 and post-88 models is that the post 88 models have footstrap inserts, which were not standard on the earlier versions, and a mast track which allows the base to be moved in a slot (although NOT a sliding mast track as such). The
almost fully retracting centreboard and footstraps makes a huge difference in performance compared to the older model.
At $500 the one in SA seems like a good deal. If it was near where I live I would buy it myself.
There was one here in Tasmania a few months back for over $1000 (from memory) which didn't last long. The "standard" price for the newer one designs on ebay or gumtree is anything from $300 to close to $1000. I think a lot of it depends on whether the seller knows that these are one of the few old school boards that can actually fetch a reasonable price.
Be aware that the mylar on the older sails can delaminate, even if they have been cared for and stored correctly. Most sails over 10-15 years old will show at least some delamination. They will still work in this state, but are well and truly on the way out by then.
Clarence
