This propulsion unit for an aquatic vehicle consists of a mobile casing equipped with an azimuth bearing due to its mounting in a pivot connection in relation to a hull element of the aquatic vehicle, the azimuth bearing having a closed volume provided to contain a hydraulic fluid, the propulsion unit having a drive shaft of a propeller, said shaft being mounted rotatably within the mobile casing by means of at least one bearing having a closed space adapted to contain a hydraulic fluid, an electrical machine being adapted to drive the rotary drive shaft in relation to the mobile casing, the propulsion unit having a supply circuit adapted to supply the closed space of the shaft bearing with hydraulic fluid.The supply circuit has a supply duct connecting the closed space of the shaft bearing and the closed volume of the azimuth bearing.