"A centerboard is a retractable keel which pivots out of a slot in the hull of a sailboat, known as a centerboard trunk (US) or case."
Our centerboards are approximately seven feet long and very heavy, I would not hazard to guess their weight.
As mentioned above, they are made of wood. Unfortunately, wood is not the most durable material in water. Happily, our 20 year old, wood, centerboards are in excellent condition.
They are controlled from the inside of the boat via sockets in the galley and in the navigation station. By inserting a regular winch handle, into the socket, the centerboards can be fully raised or lowered or anywhere in between. The socket is connected to a 4" diameter drum, a rope attaches the drum and the top leading edge of the centerboards.
To keep our centerboards in excellent condition, we are having them painted with Interprotect 2000E and then Pettit Ultima SR-60 ablative antifouling paint.