I found this on the Navionics webpage:
Cell/wifi and without signal:
To access some features of the Navionics Mobile apps, you will require a WiFi signal or cellular coverage.
1. SYNC MY DATA
2. Magazines & Guides
3. Weather (not including Tides & Currents)
4. Satellite and Terrain overlay
5. Sharing info – Facebook/Twitter
6. Downloading new map areas (government charts, Navionics Nautical charts and Navionics SonarCharts)
When offline (no WiFi or Cellular coverage) you will be able to access;
1. Previously downloaded map areas (government charts, Navionics Nautical Charts & Navionics SonarCharts) including the mapping details such as Tides & Currents, marina details and Community Edits within the downloaded mapping
2. GPS position (dependent upon if your device has a physical GPS chip)
3. Previously downloaded Magazines & Guides
4. Saved Tracks, Markers, Routes, photos
A very useful link:
http://navionics.force.com/kb/articles/ ... earch&pn=1For those that doesn't have the cell capability you can add this device:
http://www.amazon.com/Garmin-Portable-G ... nk20417-20