Note 1 to entry: A marine body can experience three linear and three rotational motions as depicted in Figure 1 and Figure 2. Positive angular and translational directions of displacement are shown by the axis labels +A, +B, +C, +D, +E, and +F.

Note 2 to entry: The principal axis is parallel to the mean water surface and aligned with the longest, plan form, dimension of the device. The principal axis for a symmetric device will be parallel to the mean water surface and aligned with a chosen direction of interest. The direction of incident energy will be through the centre of gravity and may be at an angle to the principal axis.

Key

A	Heave	D	Surge	G	Centre of gravity
B	Yaw	E	Roll	H	Incident energy at zero-degree heading
C	Pitch	F	Sway

Figure 1 – Six degrees of freedom – Floating device

Key

A	Heave	D	Surge	G	Centre of gravity
B	Yaw	E	Roll	H	Incident energy at zero-degree heading
C	Pitch	F	Sway	I	Seabed

Figure 2 – Six degrees of freedom – Submerged device