The Trolling Angles app can run on any fairly recent Android operating system (since Android 5.0, API level 21, released in late 2014), and does not require an internet connection except to show documentation and policies, and buy subscriptions.  An older retired smartphone without a SIM card or cell service can be used to run Trolling Angles and other apps like the camera, GPS apps, etc. , and can still connect to the internet over a WIFI connection when one is available. Inexpensive used Android phones are available online.

Similarly, Trolling Angles runs on older iPhones, although they are not as cheap as Androids.

Always be careful to keep your phone safe and inside the boat in case you drop it