Hit the nail on the head Hosko
Port rudder is slightly tilted to port and starbard to starboard so when the boat has for example a 20 degree lean, the leward rudder is almost vertical. You get a great deal more control when you need it.
Only really works with beamy boats, as Hosko said open 60's as per the picture in the link

Also when the boat gets a bit of lean, there is less of the windward rudder in the water therefore reducing drag

http://www.sailinganarchy.com/forums/index.php?act=attach&type=post&id=44783www.sailinganarchy.com/forums/index.php?act=attach&type=post&id=44789Hope that explains it a bit
The problem with the Inglis designed boats, is that with a transom hung rudder, it already sits high in the water, when the boat gets a bit of lean up, you loose half of the traction from the rudder therefore it is easy to stall then wipe out.