Not sure if I understand what you mean by "log", but the data stays on the watch as long as needed, until you sync it. It does not matter whether you sync in an hour or in two weeks. Just make sure there is enough of free space on the watch before you start. Remove all old activities from //GARMIN/Activity/, unused languages from //GARMIN/Text/, and delete also unneeded courses, and workouts, to free up some space, especially if you have a watch with a small memory.
Check with the cruise line you're going to use. Most have some sort of WiFi available, some free, some not, and can be used if your watch has WiFi if you set it up while on board.
I always thought GCM a conduit to the website, and it did not store any data on phone, so I never tried to sync to phone without WiFi.
