The term 'boat blade' refers to two different items used in boating. The first is a RUDDER, which is a flat piece of wood or metal attached to the stern of a boat that is used to steer it. The second is an OAR, which is a long pole with a flat blade at one end that is used to propel a boat through the water. Both the RUDDER and the OAR are essential components of any boat, and they are both referred to as boat blades.