You need to get the boat out of the water to see if it has a hull anode fitted. Probably not, but will likely have a shaft anode which is 30mm diameter. It may well also have an anode on the Prop if it is a folder or a feathering prop.
thanks for that is 30mm standard on jeanneau , we also have a fixed prop with an anode
on it any idea what size it is , boat is new to us and in the water.