Being a passenger on a seafaring vessel on Shabbat per se does not present a problem, provided that the ship is owned and maintained by non-Jews, and the majority of the passengers are not Jewish.
However, there are some issues of which you should be aware:
- One may not embark on a sea journey on the three days preceding Shabbat. This means that you may not initially board a cruise after sunset on Tuesday evening.
- A little known rule is that it is forbidden to travel more than 2,000 cubits (approximately 0.6 miles) outside a populated area on Shabbat. This is called the prohibition of techumin. Now, this does not affect sea travel because techumin does not apply if the traveler is more than 10 handbreadths above the ground, and the boat is more than ten handbreadths above the seabed. But a traveler is affected by the laws of techumin if he disembarks on Shabbat. Consult a rabbi if your plans include a Shabbat disembarkation.
- If you do disembark on Shabbat, ascertain that you are not carrying anything with you—including ID cards and boarding passes.
- We may not operate electronic automated doors on Shabbat. So scout out the ship before Shabbat to see which doors you should avoid.
- Another possible issue is keycards. Like many hotels, the passengers' doors on cruises are often operated by electronic cards—forbidden on Shabbat. You may, however, ask a non-Jew to open your door for you.
- If you are having pre-packaged meals served to you by the galley staff, be aware that you may not eat any meals which were heated for you on Shabbat.
While these are more-or-less the standard issues facing cruise goers, you would be well-advised to discuss the particulars of your trip with your rabbi, as there may be other issues unique to your situation.
Rabbi Menachem Posner
P.S. May I suggest that you explore the option of taking a "Jewish cruise"? A simple Google search will find you several companies that offer such cruises on top-flight cruise ships. You can dine on delicious kosher cuisine instead of pre-packaged fare. You will also have access to prayer services and even Torah classes. A luxurious way to pamper the body while remaining mindful of the soul's needs too!