The range of Thrustmaster’s underwater demountable azimuth thrusters are designed for easy underwater mounting and dismantling without dry-docking the vessel. This is of utmost importance to large vessels and semi-submersible oil drilling rigs to continue operation without any delays. Dynamic positioning thrusters are in service 24/7 during drilling operations. Interrupting drilling and leaving the site in order to repair a unit would be a costly decision.
https://www.thrustmaster.net/azimuth-thrusters/underwater-demountable-azimuth-thrusters/