It has to be carried. No loading into a cannon and then gliding.
Also you wont be able to keg/fire/blunderbombing runs. Glide range should be less than chainshot range. If the glider or pirate is shot, it beaks and the pirate falls with normal fall damage. No mermaid until a pirate hitswater, but canvas flapping noises for balance lol.
Now everyone tell me this won't be fun ha.
Commendations/Achievements for gliding from certain spots, barnstorming certain arches, total flight time.
Add a predatory bird to harass gliders from time to time.
Geysers in the Roar could give lift, escape from eruption hot water.