<P> The vertical / Z axis, or yaw axis, is an imaginary line running vertically through the ship and through its centre of gravity . A yaw motion is a side - to side movement of the bow and stern of the ship . </P> <P> The lateral / Y axis, transverse axis, or pitch axis is an imaginary line running horizontally across the ship and through the centre of gravity . A pitch motion is an up - or - down movement of the bow and stern of the ship . </P> <P> The longitudinal / X axis, or roll axis, is an imaginary line running horizontally through the length of the ship, through its centre of gravity, and parallel to the waterline . A roll motion is a side - to - side or port - starboard tilting motion of the superstructure around this axis . </P> <P> There are three special axes in any ship, called vertical, lateral and longitudinal axes . The movements around them are known as roll, pitch and yaw . </P>

The horizontal fore and aft movement of a vessel is called