Axis and Phase Angle Conventions

The RAO's output from Hydro (their amplitudes and phases) are based on the following coordinate system:

A right-handed coordinate system is taken with the x-axis positive forwards, the y-axis positive to starboard, and the z-axis positive downwards. The rotational motions - roll, pitch and yaw are given by the corkscrew rule, that is, positive rotations are in a clockwise direction when looking along the relevant axis. This gives a positive roll motion as starboard down, a positive pitch is bow up and a positive yaw is given when the bow turns to starboard.

All motions are calculated about the centre of gravity of the vessel.

The phase angles for all 6 degrees of freedom motion are given as phase leads measured relative to the wave trough.

By default a wave angle of 0 degrees represents following waves and 180 degrees represents head waves. A wave direction of 90 degrees represents waves incident to the port side of the vessel.