What if hardly anyone else on my sailing has it?
Your own group still works. The rest of the ship is a bonus that grows with every install.
It still works for the people you came with. If your family are within Bluetooth range — the same venue, the deck above or below — messages go directly between your phones and nobody else is involved.
What a bigger network buys you is reach. The more people aboard running the app, the more often there is somebody standing between you and the person you are messaging, and the further a message can travel while you are on opposite ends of the ship.
So on a quiet sailing, treat it as a way to reach your own group in the places a signal does not go. On a busy one, it reaches further.
If you want more of your sailing on it, the roll call board for your ship is the place to say so.
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