If a boat reached its port on Shabbat, it is permitted to disembark on Shabbat. Assuming that the boat travelled across water deeper than 10 Tefahim (handbreadths), there is no issue of Tehum Shabbat (leaving the boundaries of Shabbat). Accordingly, the Jewish passengers are considered residents of the port city and can freely walk its entire domain. Even if non-Jews erect a ramp to disembark, the Jews may use it, since it was constructed for the benefit of the majority of non-Jewish passengers.
Hacham Ovadia even permits disembarking from a ship via means of a smaller boat that ferries passengers to shore. So long as the non-Jewish sailors operate the boat for the majority of the non-Jewish passengers, it is permitted for the Jew to benefit from the service.
Of course, caution must be exercised to a avoid issues of mukse and carrying without an Eruv. Often, the ship requires passengers to present their passport to return on board, and therefore, a Halachic solution must be implemented. Also, one must insure that no violations of Shabbat are incurred as a result of triggering electronic sensors or mechanisms upon disembarking.
SUMMARY
It is permitted to disembark a ship on Shabbat via a smaller ferry.
