A system for detecting a board-insertion power-on versus a chassis power-on is disclosed. In order to reduce pressure in a piston chamber, a control circuit drives a motor for reverse rotation. In the closed position, end portions are moved toward one another, inhibiting access to the interior region. Some systems include a frame that can be anchored in a body of water. An error correcting section performs error correction processing with respect to the soft-decision value. The support is formed from a blank.