The present invention relates to a propulsion system (1) for a boat, comprising: a motor (100); a connecting arm (200); a fairing portion (208) intended for being mounted on the boat; at least one propeller (302); and a belt (2) for transmitting the torque from the said motor (100) to the said at least one propeller (302), the said belt (2) forming two belt sections between the said motor (100) and the said propeller (302).

According to the present invention, the said propulsion system (1) further comprises: a first rotary assembly (400) with the belt (2) passing there-through and capable of pivoting relative to the first fairing portion (208) about a geometrical axis directed towards the top, so as to orient the said at least one propeller (302) relative to the boat in order to turn the latter; and a second assembly (500) capable of being translated relative to the first rotary assembly (400) in order to retract the said at least one propeller (302).