Stand on a ferry deck as the harbour shrinks behind you and everything feels normal at first. The bars on your phone hold steady, messages still arrive, and the sea air makes the whole thing feel like a proper break. Then, somewhere past the last stretch of coast, the signal starts to wobble, drop and reappear in a way it never does on land. What happens to your phone in those quiet hours offshore is worth understanding before you sail, because the way it reconnects can be far more expensive than any roaming you have ever used abroad.
How far land coverage really reaches
Mobile masts are built to serve people on land, so their reach over open water is limited. A signal can carry a fair distance across the sea because there are no hills or buildings in the way, but it still fades with distance, and how far it travels depends on the height of the mast, its power and whatever sits between you and the shore.
As a rough guide, coverage often holds within a few tens of kilometres of the coast and then tails off. Close to a busy port you may keep a usable connection for a while; head further out and the network simply runs out of range. If you want a clearer picture of how patchy reach can be even on dry land, our guide to checking network coverage is a sensible place to start.
The ship's network and maritime roaming
Once you drift beyond the reach of land masts, your phone does not simply give up. It searches for any network it can find, and on many ferries and almost all cruise ships it latches onto the vessel's own maritime network. This is a small onboard system that connects to a satellite far overhead, and it is designed to keep the ship online in the middle of the ocean.
The catch is that this maritime network is billed as its own separate thing. It is not part of the roaming allowance you may have for Europe or the wider world, and the rates are set by the satellite operator rather than by your usual provider. Your phone treats it like any other network and connects automatically, often without you noticing a thing.
Why it can cost so much
Satellite capacity at sea is scarce and expensive to run, and those costs are passed straight on to you. A few minutes of browsing, a video that starts playing on its own or a run of app updates in the background can add up to eye-watering sums, sometimes several pounds for a single megabyte.
The real danger is that your phone can run up charges simply by receiving data in the background, without a single deliberate tap from you. Emails syncing, photos backing up and apps refreshing all count, which is exactly how travellers end up with a shocking bill for a crossing they thought they had spent happily offline.
Staying connected without a shock
Avoiding a nasty surprise is mostly about taking control before you lose sight of land. A few simple habits make all the difference:
- Turn off data roaming, or switch on aeroplane mode, once the coast is behind you, and only turn it back on when you are safely inside normal coverage again.
- Use the onboard Wi-Fi if you genuinely need to get online, but check the price and the terms first, as ship packages vary a great deal.
- Download maps, playlists, podcasts and anything else you want to watch or read before you sail, while you are still on a normal connection.
- Set your device to choose networks manually, so it cannot keep quietly reconnecting to the ship's satellite system each time you move about.
If you are travelling with family, it is worth walking everyone through the same steps, since a single tablet left refreshing in a cabin can be enough to dent the whole trip's budget. A little preparation means you can enjoy the crossing without an anxious thought about what your phone is quietly doing in your pocket.