When on a cruise ship, how often is it necessary to say Tefillat HaDerech? Is it just once at the beginning of the journey, or after each port stop, or possibly some other answer?
Tefillat ha-derekh is appropriate at each port stop. Also, every morning say tefillat ha-derekh without a beracha (or better yet, include it in the blessing of shema kolenu in the amidah) After arriving (safely) at your destination, say berkhat ha-gomel.
Hey, you paid for the journey, get your blessing's worth from it!
Rabbi Rashi Simon