Propulsion unit for a marine vessel

A propulsion unit for a marine vessel, the propulsion unit comprising:

• a shell structure mountable below a hull of the marine vessel such that the shell structure is at least partially immersed in water, when in use;
• a shaft extending between an inside and an outside of the shell structure through an opening provided thereat;
• a propeller coupled to the shaft outside the shell structure so as to be rotatable by the shaft;
• a shaft seal arrangement comprising a plurality of seal lips axially spaced apart from each other and engaging the outer circumference of the shaft, such that at least a first seal chamber is delimited between adjacent seal lips and the outer circumference of the shaft, and
• a first lubrication arrangement, in turn, comprising:
• a first lubricant circulator;
• a first lubricant feed line for conducting a first lubricant to the first seal chamber via the first lubricant circulator, and
• a first lubricant return line for conducting said first lubricant from the first seal chamber back to the first lubricant circulator,
• wherein the first lubrication arrangement further includes a first lubricant heat exchanger arranged at least partly in contact with an outside environment of the shell structure for conducting the first lubricant through the first heat exchanger and for transferring heat from the first lubricant to the outside environment of the shell structure, and
• wherein a portion of the first heat exchanger outside the shell structure is provided on an outside end surface of the shell structure facing the propeller.