: Bjorn has a retractable under hull rudder idea drawn on his Sea
: Racer plans. Picture a skeg box that then pivots when down.
: Pretty ingenious. Not sure if anyone has built it.
Hi Dan,
Lightspeed kayaks has had a similar rudder approach for quite some time (image from side shown) - with the exception that the 'housing' is just a depression in the hull. The main issue with a tight fitting housing is getting the rudder back in alignment to retract.
Lightspeed get around it by having the large depression so any old orientation will work; Bjorn could get around it by having a detent that deploys or a detent or offset can be felt when both rudder pedals were slightly pushed at the same time. Then retract with the other line - idea anyway.

Will,
That type of rudder is sometimes termed a drum rudder. With the obvious deadrise angles in your drawing, it just might make some sense to tip the rudder somewhat and put it off the centreline and vertical to one of the deadrise angles - as they seem to be fairly flat. (Possibly 2 small ones in tandem on opposite sides?). As you won't have access to the top of the rudder to push it down(when paddling), it would make some sense to have an (a pair?) actuating line down to the bottom of the drum to deploy(similar to the pair that Bjorn has, but for linear pulls vs a rotators)