Coupling structure and coupling method for power transmission

A coupling method for a power transmission comprising a propeller shaft, which transmits a rotational driving force, and a rotation-transmitting device, which is connected to said propeller shaft and transmits the rotational driving force, said propeller shaft and said rotation-transmitting device being connected with each other by said coupling method, which comprises:

• measuring a direction of a rotational unbalance of said propeller shaft as a single part;
• providing said propeller shaft with a first mark that indicates the direction of the rotational unbalance of said propeller shaft as a single part;
• measuring a direction of a rotational unbalance of a companion flange as a single part, said companion flange to be connected to said propeller shaft at said rotation-transmitting device;
• providing said companion flange with a second mark that indicates the direction of the rotational unbalance of said companion flange as a single part, one of the directions of said rotational unbalances indicated by said first mark and said second mark being set as a direction along which a rotating mass becomes larger while another being set as a direction along which a rotating mass becomes smaller, and one of said first mark and said second mark being provided over an angular region with a predetermined angle around an axis;
• and
• positioning rotationally said propeller shaft and said companion flange such that the one of said first mark and said second mark that is provided over said predetermined angular region is met by the other, for connecting said propeller shaft and said companion flange.