Abstract: Invention relates to a thruster assembly for a marine vessel including a body including a duct having a longitudinal axis, and a first end and a second end, a support structure for a propeller including a propeller shaft at a centre line of the duct, a propeller, positioned into the duct and being attached to the propeller shaft, wherein the propeller including at least three blades and a boss which is supported to the shaft, and further a circular rim to which radial ends of the propeller blades are attached, wherein a circumferential slot is provided, opening inside the duct between the first end and the second end, into which slot the circular rim is arranged to extend radially, and at least one gas inlet arranged to open into the slot. Invention relates also to a transverse tunnel thruster and a steerable azimuthing thruster provided with the thruster assembly.