A method of handling a unit arranged in a watertight hoisting chamber opening into a hull of a vessel is provided. The unit is adapted to extend into the water below the vessel when installed at its mounted position. The unit is clamped in its mounted position by clamping means and releasing fixing means fix the unit into its mounted position while holding the unit clamped in position. The hoisting chamber is at least partly flooded, the clamping means are simultaneously released and the unit lifted from its mounted position by applying a lifting force to the unit by lifting devices, and the unit is hoisted away from the hoisting chamber.
