IMU sensor does not show the orientation of the vessel in ignition sim

Hi all,
i am working on a project which involves water and ship simulation. I have a ship model which can float on a waves using the plugins available with mbzirc(GitHub - osrf/mbzirc: Simulator for the MBZIRC Maritime Grand Challenge) repository.
i am trying to measure the ship’s movement in all direction

using the IMU sensor. Although the ship is moving largely in z direction, IMU sensor data shows 0 in z direction. Can anyone help me in this regard.

This kind of questions is best asked at the Robotics Stack Exchange, as this forum is rather intended for general conceptual discussions and questions.

That being said:
I have no experience with the IMU sensor, but I notice that the legends of your graphs state ‘orientation’ and ‘roll-pitch-yaw’, i.e. rotation, whereas you mention “moving largely in z direction” which I interpret as translation.

According to this description only linear acceleration is reported.

See also this documentation.

Thank you for your response. I would ask the question on robotics stack exchange as well.