Sailing with no signal: what works on your iPhone and what doesn't
By Luis Carvajal · Updated 1 October 2026
In short: your iPhone's GPS works with no signal, airplane mode included. What drops out is everything that has to be downloaded: the chart (unless you saved it beforehand), the forecast, wind and sea. So download the chart in port, on wifi, and check the forecast before you leave.
In the Balearics you only have to round a headland to lose every bar, and a few miles offshore coverage disappears altogether. That is exactly when knowing where you are matters most. The good news is that the essentials do not depend on the network.
What works offline and what doesn't
| Offline | Why |
|---|---|
| ✅ Your GPS position | GPS is a receiver: it listens to satellites and uses no data. Without a network the first fix takes longer (a couple of minutes instead of seconds); after that it works the same. |
| ✅ The chart, if you downloaded it | If the app stores the area on the phone, the chart is drawn from there. |
| ✅ Recording the passage | The track is stored on the phone; nothing needs uploading. |
| ❌ Chart you didn't download | Most apps fetch it in tiles as you go. With no signal, that tile never arrives. |
| ❌ Forecast and warnings | They are fetched live. Check them before you leave. |
| ❌ Live wind, sea and tide | They come from online weather models. |
What to prepare in port
- Download the chart for the whole area, not just the destination: the route too, and the fallback anchorages in case the wind shifts.
- Check the forecast and the warnings in force, and how the wind will develop overnight if you plan to anchor.
- Charge the phone and carry a power bank or a charger on board.
- Keep the official chart at hand and the navigation equipment the regulations require. The phone is an aid, not the plan.
At sea, the radio is still the source of the forecast: in Spain, Salvamento Marítimo announces it on VHF channel 16 and broadcasts it on its working channels.
How Offing does it
Offing carries its own chart of the Mediterranean. In port, put the area you are going to sail on screen and tap "Download the area I can see". Before it starts it tells you how much space it takes, and you can delete areas when you stop sailing there.
- The chart is drawn from the phone: zoom, pan and look things up ten miles offshore in airplane mode.
- Balearic seagrass travels with the downloaded area, so the seagrass warning works in the cove where you are about to anchor even with no signal.
- The passage is always recorded on the phone, signal or not, even with the screen off.
- What needs signal it says plainly: the forecast, sea state, wind, tide and the seabed at a point.
Frequently asked questions
Does the iPhone's GPS work in airplane mode?
Yes. Airplane mode switches off the radios that transmit, but the GPS receiver keeps working. Without data it just takes a little longer to get the first fix.
Can I use Google Maps or Apple Maps at sea?
They are not nautical charts: no depths, no buoyage, no hazards to navigation. At sea you need a nautical chart.
How much space does a downloaded area take?
It depends on the size of the area. Offing works it out before the download starts and, if it is too big, asks you to zoom in.
Offing
Offline Mediterranean chart, Balearic seagrass, the official forecast and a logbook that writes itself. iPhone and Apple Watch, one payment.
