savvy navvy supports "offline mode" where you can download your charts of offline use. This is currently available on your phone of tablet for Android devices.
iOS is coming soon but sadly takes a little longer to release new updates, but we'll be sure to let you know when it's live.
Offline mode is not available on desktop so be sure to use your phone or tablet. Here are some screenshots of where you can find the download chart option in your app.
Click on the three hashes on the top left of your screen:
Then click off "offline charts":