Navionics boating
I don’t use it much so don’t remember what it takes to get it to work
Maybe like google maps offline , you might have to download a portion or keep the app open as you go out of service.
But it’s like a hiking app AllTrails, you can save your rout and spots
It has some depth charts that aren’t very accurate, you see your speed and direction and location
It uses up battery life pretty quickly
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