The invention relates to a machinery arrangement for a marine vessel (1), which machinery arrangement (2) comprises a combustion unit (3), an exhaust gas duct assembly (4), which includes a first branch pipe (41) and a second branch pipe (42) and is connected to the combustion unit for receiving an exhaust gas flow and for leading the exhaust gas flow to the atmosphere, and an exhaust gas cleaning system (5) arranged in a flow direction of exhaust gas. In order to achieve an improved cleaning of the exhaust gas, a fan unit (6) and a first valve means (7) is provided in flow connection with the first branch pipe (41), which is connect to the exhaust gas cleaning system (5).