Rob,
To quote from the BR20 manual:
"Self Righting, Side Decks, and Asymmetric Capsize Buoyancy
"If you capsize when the ballast tank is empty, the boat will lie on her side with the rig on the water. In normal conditions she will not turn over completely. If she does, due perhaps to wave action, or crew members hanging onto the sides of the up turned hull, then she can be recovered single handed if necessary, thanks to her unique Asymmetric Capsize Buoyancy (ACB).
"Side decks are very important to create a boat that is self righting from 90 degrees, but unfortunately, they hinder recovery of a vessel that has fully inverted. The BayRaider mast is a hollow sealed unit, aiding recovery, but without ACB, the boat is still too stable in the inverted state for one man to be able to right alone.
"ACB allows one side deck tank to flood, thus destroying buoyancy on one side. A baffle on the port side under the foredeck (EPOXY PLY BOAT ONLY) protects the tank from flooding in the 90 degree knockdown case, but when fully inverted, the tank entrance is exposed and water pours in. On GRP, GRE and CRE boats, the inlet for this water is the wooden lined hole on the port side next to the mizzen. Once the boat has been righted, the majority of the water pours back the way it came in, landing in the floor well (or Outboard well - GRP boats), from where it can flow out the outboard well. The remaining amount floods into the floor well via a small drain hole into the port side seat locker. You can feel for this with your hand in the locker, reaching outward and upward (epoxy ply only).
"If your boat is capsized with the water tanks full, she will of course self right. It is unlikely she will ever get as far as a full invert in this state as her angle of vanishing stability is an impressive 120 degrees, but if she does she can be recovered in the same way as if the ballast tank were empty."
Here's a video of the system in action
http://m.youtube.com/#/watch?v=xvNj2Mj4JZg&desktop_uri=%2Fwatch%3Fv%3DxvNj2Mj4JZgIt has also worked in real life during last year's Sail Caledonia, when a BR20 completely inverted and was quickly righted without assistance from the safety boat.