Electric propulsion units

A propulsion unit arranged to propel a water borne vessel comprising an electric motor, arranged to provide propulsion, and a housing ( 4 ), arranged to contain the motor, the interior of the housing ( 4 ) being maintained at an increased pressure of above roughly 2 bar to increase the cooling effect of a cooling gas maintained therein. Further, it is disclosed that for the propulsion unit to comprise a housing ( 4 ) that contains the motor, wherein an end region of the housing is provided with a heat exchange mechanism ( 59 ) arranged to cool cooling gas passing thereover, the heat exchange mechanism being associated with the housing such that, in use, water surrounding the housing absorbs heat therefrom. The unit can be arranged to make use of either, or both, of the features.