Flip the boat over (deck down) and carefully inspect the seam between the hull and deck on the gunwhale.  There is a glue line that can develop a small crack when/if the hull hits a dock or some other object.  When sailing upwind (sail sheeted hard and hiking out) the boat is loaded up and that crack can open and close as you go through waves (panting). Also look at the seam on the edges of the transom just below the gudgeons.

If you find a crack, my suggestion for the cracks on the sides is to use a dremel to grind out the old adhesive and replace it with West System G-Flex epoxy.  For cracks you may find in the transom seam, I inserted several wooden tooth picks to open up the gap and allowed epoxy to be inserted.  If you are not comfortable with this type of repair, check with your local RS Rep.  Good luck.