On my 20' FD center board sail boat we would make to slot over sized and put point shims on the axle and one or two other spots for a no slop fit. We did not use jibing center boards do to the speed of these rockets,(15 to 20 knots). To keep the flow clean we epoxyed a piece of heavy mylar over the slot and after cure would split it with razor knife.The mylar looks like a midwing root fairing when down.You still would have reach under after launching to open the slot to clean out the sand put hopefully would not bind. Maybe you could put the out flow of the foot pump to blow it out, a quik roll with skirt open to let some in:)
Don
: Loaned my VCP Avocet RM to a buddy. He bent the skeg cable.

: So, in replacing the skeg cable, I decided to build a nicer skeg. The stock
: skeg was some sort of stiff (PP or PVC) plastic, 1/4" thick, rounded
: over edges, but flat in cross-section.

: When I fixed my friend's old VCP Selkie, I noticed it had a foil-shaped glass
: blade. I can do that!

: The new skeg is white HDPP, 1/2" thick. Cut profile to match existing.
: Leading edge rounded over to 3/8" back from edge. Trailing edge is
: cut to a fine taper about 1 1/2" back from the edge. As good of foil
: shape as I could cut with a block plane. There were two rubber spacers
: which centered the old skeg in the skeg box. These were removed to make
: room for the new, wider skeg.

: Photo shows: (top left) Original skeg
: (lower left) New skeg
: (center) Deployed new skeg showing cross section shape
: (right) Left, old skeg thickness; Right, new skeg in box, twice as thick.

: After using this skeg last night, it was a lot less noisy when deployed. It
: also seemed to have less drag, but that is what I was expecting, so this
: is a pretty subjective measurement. I know with the old skeg, when I was
: cruising and dropped it quickly, I felt like I hit the
: brakes...quantitative tests say you gain up to 10% more drag with a skeg
: deployed. The new one "feels" like less than 5.

: It used to be susceptible to 1/4" - 3/8" gravel. Guess now I'm
: susceptible to -1/8" gravel!

: Shawn