One of two steel plates, port and starboard, whose forward parts are bolted to the ground ways supporting a ship about to be launched, while their aft parts are attached to the sliding ways; at the start of the launch, they are cut simultaneously with burning torches to release the ship. Also known as soleplate.

1. A member attached to the bottom of the rudder of a wooden ship, which brings it down to the false keel.

2. A member which joins the sternpost and the rudderpost of a wooden ship.

3. A projection from the keel of a ship.