² three rotations about these axes:
– roll about the x-axis, positive right turning,
– pitch about the y-axis, positive right turning, and – yaw about the z-axis, positive right turning.
These de…nitions have been visualized in …gure 3.1.
In many cases these motion components will have small amplitudes. Any ship motion is build up from these basic motions. For instance, the vertical motion of a bridge wing is mainly build up by heave, pitch and roll motions.
Another important motion is the vertical relative motion, de…ned as the vertical wave elevation minus the local vertical motion of the ship. Thus, this is the motion that one observes when looking over the rail downwards to the waves.