S-57: .000 with .001… updates, or .zip. Folder: e.g. ENC_ROOT from a USB stick. Tap a chart object to see what it is.
Gulf of Finland, Neva, Ladoga:
Water shallower than draft plus margin is dark blue, the bold contour bounds safe water. The route and the course ahead are checked for shoals.
Signal K brings depth, speed and course from the boat's instruments over Wi-Fi. Free NOAA charts cover US waters only: tap the map outside loaded charts to find one.
Device code:
Prototype. Not for navigation.