Fig. 16-6 - When the rudder blade extends beyound the transom, a cavitation plate should be mounted over it, in line with the bottom, to prevent air from being sucked in during turning. There is a wooden catitation plate shown at the bottom of the photo. This boat had a drain plug on each side of the keel. To test the effectiveness of the cavitation plate as a cure for a steering problem, the wooden plate was made and held in place with bolts through the drain plug holes. In this case, the cavitation plate cured the problem.