I'm not too familiar with the Clipper Marine
21 but regardless, I'm having some trouble understanding what you mean. What screw are talking about that won't go through the keel housing and keel? Are you perhaps talking about a centerboard
trunk cap, that might not be in place? Water normally sloshes up and around the CB Trunk when you are sailing relatively fast, but it is normally blocked from coming into the boat by some sort of a cap on the trunk.
Check the position of the down CB when you are at the dock
and mark your control or CB wire.