There is an on-going Tern survey project, which takes place mostly on weekdays. May be you can join the surveyor and take some good photo. The Tern Research Group also have weekend surveys. If you know them (Alan, me and others), you may contact them for information.
In general, breeding this year has been fine on several Tern Islands. For photography, riding a ferry would not offer much chances. You may want something more adventurous. Remember, HKBWS recommends not to land on the breeding islands when Terns are breeding.
HF Cheung