The last passenger liner leaving the wharf of Hidden Dragon Island each day was 7:00 pm, after which, passengers could only leave at 6:00 am the following morning. Unless there was a special situation causing them to leave by airship, people could only leave Hidden Dragon Island on a passenger liner.
The alleged special situations referred to the privilege for some members and agencies of the Zhang Clan to access Hidden Dragon Island by airship. Of course, Zhang Clan's airships could not be taken by commoners; additionally, the airline to Hidden Dragon Island had not been opened, therefore, it was impossible for commoners to leave the island by airship.
The airline distance between Hidden Dragon Island and Jinhai City was over 140 km. It was a four to five hour journey on a passenger liner. Perhaps there wasn't only one person who could swim over 100 km in water, such as some senior fighters, whose physique and swimming skills were exceptional.
[1] Shar-pei is a kind of Chinese dog. It's the guy's nickname.