forget it.
all ferries which go to macau, guangzouh and shekou are closed shipbodies. You have to photograph behind a window. 1st class is upperdeck, the windows are a bit larger and a little bit more clean. near the ferryterminal on hong kong island you can take some nice pictures. I'm more familiar with HK Island and not so with Kowloon so I can only give information about this side.
I normally look for a ferry with open balkony near the star ferry. I think the name is peer 1 to 5(?) and the shipspotting tour can start.
also very good is take the bus to Cyberport there the vessels will pass you very near.If you have enough money you can stay there at Le Meridien hotel.
Peter