Originally Posted by tweeds
Given I want it to support my son windsurf training in Hayling Bay, I guess it's probably a rib I need
Interestingly I'm not sure it is.
Windsurfers tend to go out in conditions where everyone else is coming in! Willk is right that for normal boating 20 kts would not be too much fun in a SIB for long periods. The normal school of thought is rough weather = bigger boat. BUT windsurfs, big waves, close to shore, aren't ideal for big boats.
If it were me, I would be looking at the sort of thing the surf rescue guys use - small, fast, highly manoeuvrable, easy to right if it goes wrong, soft floor if you get thrown about etc...