What’s the best way to get to the remote Okinawan islands?

We're traveling to Okinawa in a few weeks and are interested in visiting some of the remote islands, like Ishigaki or Zamami.

We have our hotel in Naha, but are there ways to book a day excursion in these places? Is this something we have to arrange for on our own – like a ferry or seaplane?

Any advice is welcome!