Actually, as a priest myself, I can tell you that priests are not obligated to celebrate Mass everyday. They are held to the same obligation as any other Catholic: Mass on Sundays and Holy Days of Obligation. Now, in the "older" Church, there was a certain obligation/expectation to celebrate Mass daily, but not now.
That being said, we generally celebrate Mass daily.
And, when I cruise, I usually offer the cruise director to say Mass for any of the passengers on board. Often they accept the offer and, on ships that do not have chapels, we have Mass in a large capacity place such as a theatre. (That is where I have had Mass on the Magic -- in the movie theater.)
Candles -are- used then. The place is set up by the crew and they remain to monitor in case any need arises.
What a priest needs to be aware of, though, is the line that he is sailing on. Most lines have Mass supplies -- chalice, books, wine, hosts, et cetera. Some lines, like Disney, do not have those supplies. If we do not bring our own, we don't have Mass.
Additionally, many lines try to ensure a few different traditions for services: Catholic, Protestant, and Jewish. Some lines have a chaplain assigned to every sailing (Holland America is great for that) and some lines just have ministers on board for the "biggies" of Christmas and Easter.
I would never want to be a ship chaplain, though. They are a part of the crew and are assigned crew quarters. Hardly spacious. They are also restricted to where they can be. On lines that have casinos, they are usually not allowed in there and some do not allow them in the bars.
Going as a passenger and volunteering to celebrate Mass is entirely different, however.
Well, this was kind of lengthy and somewhat off topic and on topic. Hope it helps answer some questions.
