I’m programing to make a cruise with my family.
The cruise will start not on Shabbat and will end not on Shabbat. My question is, if the cruise docks on Shabbos, can I disembark? If I will go not fare from the pier,and no bring any ID card or other, can I start to consider the the techum limit from the pier?
There is no prohibition in disembarking on Shabbos.
However, because there is no eruv binding the ship to the dock, carrying is forbidden. As you note, you will have to ensure that you have nothing in your pockets.
The techum (boundary) begins at the dock and extends approximately 7/10 of a mile, and you have to take care not to walk too far in a non-residential area.
Note that you can begin the cruise from Sunday to Wednesday, but not on Thursday-Friday.
Apologies for the delay in replying to this question.