As originally posted by Paul:
A word of warning for Sidewinder owners. There are a lot of centerboards at the bottom of many lakes out there. If the boat turtles, the board will almost definately fall out of the slot. If it is not secured strongly to the boat with a line it will sink to the bottom of the lake. Even if the boat capsizes there is a chance the board will fall out.
Make sure you have a line attached to the board and the boat!
When I bought my boat the previous owner made an L-shaped bracket that fits partially into the slot and is screwed to the aluminum running along the top of the centerboard slot. It works very well but you cannot take the board out of the slot unless you have a screwdriver handy.