The ferry leaves Piraeus for Crete, or the cruise ship sails out of Dubrovnik, and for a while your phone carries on as normal. Then the coast falls behind and the signal changes: it may vanish, or it may come back under an unfamiliar network name. That second case is the one behind surprise bills.
This guide explains internet at sea on a cruise ship or ferry: why land signal fades, why the ship's own network is billed separately, three ways to stay in touch, and how to make a small data plan last.
Key facts for internet at sea
- Near the coast and in port: phones connect to land networks
- Further out: some ships and ferries run an onboard mobile network, usually switched on only away from the coast; not every ship has one
- Billing: onboard networks are not part of Roam Like at Home; home operators bill them separately, often at high rates
- Maritime plan: works on ships that run an onboard mobile network, from 100 MB for seven days to 5 GB for 30 days
- Sea rescue: 112 in all EU countries; 195 in Croatia, 108 for the Greek coast guard, 196 in France
How mobile data works at sea
Mobile networks are built on land, so their signal reaches only so far out to sea. Near the coast and in port, your phone stays on land networks, where Roam Like at Home applies as usual for an EU SIM in an EU country. Beyond that, there is either no signal at all or the ship's own onboard network.
An onboard network is the ship's own small mobile network, linked to the outside world by satellite, and your phone sees it as just another network to roam on.
Why ferry and cruise bills get so high
Onboard networks are not part of Roam Like at Home, so even on a ferry between two EU countries, home operators bill them separately, often at high rates. A phone syncing photos or updating apps during a crossing can run up a charge before you notice.
To stop your home line using data on the ship's network, turn its data roaming off before you sail; to keep the phone off that network altogether, use aeroplane mode with Wi-Fi switched back on.
Three ways to stay in touch at sea
- Wait for land. Near the coast and in port, your usual plan or travel eSIM works, and Croatian island ferries stay close enough to land for most crossings.
- Use the ship's Wi-Fi. With aeroplane mode on and Wi-Fi switched back on, the phone stays off every mobile network, the ship's included.
- Use a maritime plan. Telcomia's maritime plans work on ships that run an onboard mobile network: 100 MB for seven days, or 500 MB, 1 GB, 2 GB or 5 GB for 30 days. Because data at sea costs far more than on land, the plans are small.
Which plan fits your trip
Short coastal hops that stay near land may not need a maritime plan. For a long crossing or a cruise with sea days on a ship with an onboard network, it keeps messages and essentials coming.
For the days in port, a land plan does the work: compare the destinations listed on Europe plans or Caribbean plans with your ports. Telcomia's standard plans are data only, with calls through apps, and each plan's details show the Activation line, the duration, the data and whether you can share the connection with other devices.
Before you leave
- Check whether your ship or ferry runs an onboard mobile network before you rely on the maritime plan.
- Install your eSIMs at home on Wi-Fi before you sail.
- Turn data roaming off for your home line before the ship leaves port, and on for the eSIM you are using.
- Use the maritime eSIM as your data line at sea and your land plan in port; if that is your home line, turn its data roaming off again before you sail.
- Turn off automatic app updates, photo backups and video autoplay while you are at sea.
- Download tickets and offline maps before you sail.
Consular protection: emergencies at sea
- 112 works in all EU countries; in Croatia, 195 is the sea rescue number, in Greece 108 reaches the coast guard, and in France 196 is for emergencies at sea. From a mobile they need a signal, which near the coast comes from land networks.
- In Croatia, Greece and France, embassies are in Zagreb, Athens and Paris, with consulates on some Greek islands and in several French cities. The Telcomia app shows which mission is responsible for you, with address and phone.
- Emergency phrases in Croatian, Greek and French are ready to show on screen in the app.
Questions travellers ask about internet at sea
Can I use mobile data on a cruise ship?
Near the coast and in port, yes, on land networks. Further out, only if the ship runs an onboard mobile network: your home operator bills it separately, often at high rates, and a maritime plan works on it too. Otherwise, use the ship's Wi-Fi.
Why was my roaming bill so high after a ferry?
Your phone probably joined the ship's onboard network once the coast was out of range. Those networks are not part of Roam Like at Home and are billed separately, often at high rates. Next time, turn data roaming off for your home line before you sail.
Does EU roaming work at sea?
Only on land networks, near an EU coast or in an EU port. A ship's onboard network is not part of Roam Like at Home, even on a crossing between two EU countries.
How much data do I need at sea?
Plan for messages and essentials rather than streaming. The maritime plans run from 100 MB for seven days to 5 GB for 30 days, and switching off automatic updates and backups makes a small plan last longer.
The short version
At sea your phone is on a land network near the coast, on the ship's own network further out, or on nothing at all. Keep data roaming off on your home line so it cannot run up a data bill on the ship's network, and use the ship's Wi-Fi, or a maritime plan if the ship runs an onboard mobile network, for messages.
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