A propulsion chain (8) for a ship (6) including a main heat engine (18); at least one secondary electrical power house (26) powering a distribution panel (34); at least one transmission line (16) provided with an end propeller (14) and mechanically coupled to the main heat engine (18) to drive the latter; at least one rotating electrical machine (22) mechanically coupled to the transmission line (16) and powered from the distribution panel (34), a mechanical coupler (20) able to be freed from the main heat engine (18) and the rotating electrical machine (22) arranged on the transmission line (16), between the rotating electrical machine (22) and the main heat engine (18). A synchronizer (60) for synchronizing the speeds of the rotating electrical machine (22) and the main heat engine (18) before coupling of the rotating electrical machine (22) and the main heat engine (18), and an engager for engaging the mechanical coupler when the speeds of the rotating electrical machine (22) and the main heat engine (18) are essentially equal, i.e. correspond.