How can I destroy the flag without falling to my death?
I've never had much problem. I have various methods of climbing ships.
Usually if I have to capture a flag my tactics are after boarding starts
- Use the swivel gun to do what damage I can.
- Use the quick elevator thing on my own ship to get up to the platform.
- Shoot enemy soldiers on the central platform (or others).
- Swing across to their boat on a rope and assassinate people and then fight generally til I am at or close to the soldier death limit (if one or two short I hope that my crew will finish the job).
- Use the quick elevator on their ship to start my ascent. There is of course no soldiers up there any more.
This has never really failed me. I do occasionally skip some steps but the above is, in my view, pretty efficient and pretty foolproof.