Be aware that cruise ships are required to turn off their wireless networks when they are 9-12 nautical miles from land and while in port. Also:
When the ship's wireless network is on, your device will indicate you’re roaming on its network by showing Cellular at Sea, 901-18, or NOR-18 in your display.
When your device is roaming on a land-based carrier, it displays the land carrier's network information.