The Pacific Ocean is massive and if a ship turns off its transponder it is invisible unless you have satellites in your game.
So it seems like the key will be some combination of deactivating the transponder, getting away from other ships, being low profile in various EM wavelengths (difficult if it's also large), traveling with a significant cloud cover (hurricane?), escaping detection by military submarines and other sonar sources, and ending up in a place and condition where they're sheltered from all of the above. This seems very nearly impossible if everyone is already hunting for our intrepid vessel, but if there's some reason for people not to be looking right away, I can imagine plausible scenarios where the data takes long enough to come together for the necessary storytelling beats to play out.