1. Field
Embodiments of the present invention relate to a propulsion apparatus for ships and a ship including the same.
2. Description of the Related Art
Contra-rotating propellers are an propulsion apparatus that may achieve high propeller efficiency by causing a rear propeller rotating in a direction opposite to the direction of rotation of a front propeller to receive rotational energy produced by the front propeller and convert the same into propulsion power (hereinafter, referred to as ‘a contra-rotating propulsion apparatus’).
In the case of conventional contra-rotating propulsion apparatuses, a rear propeller and a front propeller are respectively attached to a main shaft and a hollow shaft which are coaxially disposed and rotated in opposite directions by a planetary gear unit.
To effectively use such a contra-rotating propulsion apparatus, a very large planetary gear unit may be required. However, it may be very difficult to secure a space for installation of such a planetary gear unit of this size at the stern of a ship formed in a complex shape.
In addition, in the case that the planetary gear unit malfunctions, operation of the apparatus may be interrupted. Thereby, the propeller ceases to rotate and accordingly propulsion may be lost.
To secure the space for installation of the planetary gear unit, the planetary gear unit may be deployed in a forward position. In this case, the length of the hollow shaft increases by the distance that the planetary gear unit is moved. However, as the length of the hollow shaft increases, the area that needs to be lubricated to reduce friction between the hollow shaft and the main shaft may increase, and alignment work through installation of bearings in the shaft may become difficult.