As always things are not that easy as they seems, first I hand sand down the bow thruster hole and then I sand down the engine leg and the edges of the rudder.
I thought the keel was a easy job but I was wrong, it is almost impossible to sand down with the sander so I get my old 600W Bosch grinder, 5 grinding discs later I reach my goal and I can then apply some rust converter as the first part in the process.
IMPORTANT : Do not get the rust converter on the skin !!