The android ap "Currents" works fantastic for scoping out currents in places like this.
We like to have 2 vhf radios, one on 16 and one on 13. Make a security call on 13 before Hell Gate. It's a blind corner. The harbor below the battery is more difficult than the Gate, watch for the ferries. Consider going behind governors island to avoid the ferry terminal if you are coming through during weekday rush hour