On my M-23 ("Robin's Nest"), the stock rudder extended almost 9" below the fixed keel depth (board retracted). The few times I ran aground, it was the rudder that buried first in the mud/sand hee in the Chesapeake. One time, we hit a dredging pipe with the rudder tip as we motored out of the marina - a dangerous scenario. It spun the boat around and could have damaged the transom. The M-23 rudder, owing to the Boomkin, could not be made retractable. So I made an entirely new rudder by laminating junk pieces of lumber with System Three epoxy and sanding/planing to shape. I made it an accurate constant chord using a NACA0012 foil shape and I made it about 2 - 3 inches shorter than the fixed keel depth, considerably shorter than the original asymmetric rudder. But, because the chord was constant and longer than the original rudder shape, I gained 33% in rudder size. and I added a diamond-shaped end-plate, maybe 16' wide. End-plates may be controversial, but the improvement in performance was dramatic. I can't remember the last time the boat rounded-up. The improved grip also resulted in more low-speed authority when motoring. The finished rudder was finished with several coats of epoxy barrier coat and the necessary bottom paint. The end plate (no foil shape) was cut from sheet PVC. Jerry Wolczanski M-23 "Robin's Nest" Flag Harbor Marina St. Leonard, MD