Hi Tony,
Water temp in Langebaan is on the other side of warm my guess is around 12-15degC.I`d recommend a full-length wetsuit. The Lagoon is warmer but I think you`ll be sailing more in the Bay north of the island (Saldanha Bay) as the lagoon shallows considerably from the island going south. Air temps should be 22-30degC, sometimes up to 34. Wind chill can be a factor if a cold front is pushing through.
I windsurf there more than catsailing, and haven`t seen a shark yet. Apparently the fishermen catch small ones that probably come into the shallows to find food, or for safety from bigger ones. Having said that I make sure I waterstart as quickly as possible when falling in, I share your concern about them ! There is a fish canning factory at the town of Saldanha, if there are any sharks they would probably hang around there waiting for scraps. We normally sail our nationals there, and have not seen a shark yet, or lost any competitors <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" /> (and I have been crowned the capsize king after 4 ditches in one downwind leg of a race <img src="http://www.catsailor.com/forums/images/graemlins/mad.gif" alt="" />)
We have seen a whale in the lagoon, and had to tack to avoid getting too close, but it`s not the time of year you are likely to see any.
Wind should be good, if not a little too good based on what we have had lately. Our REALLY windy season is normally from November to mid-Feb, then starts tapering off into March, but it started late this year, and seems to be hanging around.
Have a look at Google Earth, search Langebaan Lagoon / Saldanha Bay. There is a "join" line in the map where the satellite images overlapped. The sailing area is likely to be just about where the darker image meets the lighter image, just north of the small island in the lagoon mouth. Launch beach is to the right of the island, in a narrow channel.
Hope this helps, enjoy your regatta. I might come up there for a day or two to watch and windsurf, what`s your sail number ?