Used to sail Lightnings - I had a wooden one (#6750, Finkelday, Essex, CT). Top corner of the centerboard had a pin that rested on the centerboard case when fully lowered. A friend with a wooden boat sailed over a rock that raised the board, board came down and the pin hit the stop on the case. Momentum of the board lifted the whole case off the keel at the fwd end and sank the boat.