Thanks for reaching out.
I would recommend contacting Galway Bay Boat Tours
to try and organize boat hire for your trip. Doolin Ferries
may also be a possible contact who can put you in the right direction. Failing that some of the Galway Facebook groups can arrange or have contact details for private boat hire, so it may be fruitful asking on there. Low tide gives at least two hours to wander around the island.
I hope this helps. Let me know if you have any other questions.