When Batman and Robin go to investigate the suspicious buoy, they drive the Bat-Boat and talk about the disappeared ship and commodore Schmidlapp. At one point, Batman tells Robin to look for suspicious ships. When he says this, look closely the sea behind. If you watch carefully enough, you can see a motorboat behind them.(You might want to rewind to see it.) Soon after this, Robin looks at the Bat-boat's dashbar and says: "It looks like we've got the whole ocean for ourselves!"