Ok i have noticed, and I'm not sure if this has already been picked up on yet if so i apologize, that the great admiral can cross oceans as soon as medieval era without the need of astronomy. It's useful but I'm not sure if it's working as intended as it seems a bit unusual to be doing exploring this way when i still have triremes and i haven't had the chance to test out whether that extends into earlier eras and if it's possible then, i haven't yet been able to get a great admiral that early.

However it does slightly bring into question of the necessity of having astronomy if you can just get your great admiral to do exploring, which you can now get as soon as you get Commerce tree opening upgrade. Just a thought thanks.