A cavitation plate is the adjustable metal plate that runs along
the bottom of the transom on a V-drive. Some people call the flat
metal plate on an outboard or outdrive a cavitation plate but the
correct name is anti ventilation plate and cavitation and
ventillation are not the same. It is similar in function to Trim
Tabs. A cavitation plate is used to adjust the trim of a V-Drive
and keep the nose on the water. Here is a link to a picture on
PerformanceBoats dot com
In this picture of a V-drive, the cavitation plate is anodized
red.