The best free GPS tracking app for Android that we are aware of, OruxMaps, is currently preparing the launch of a new nautical version, that works with AIS
As you can read in this forum post http://www.oruxmaps.com/foro/viewtopic.php?f=4&t=1627 there is a new version of OruxMaps that is focused on sailing requirements.
It has a list of on-line maps (OpenSea maps) and you can load your own, as explained in this manual.
Plus you can convert the on-line maps into off-line.
The most interesting part is that it decodes the AIS NMEA sentences that can be received via IP, USB or Bluetooth.
We are sure that this program will become a reference in the category of nautical mobile apps, since it has already become the best free app for trekking.
We are currently testing this app, that is currently in beta if you would like to get in touch with us please make use of the comments section below.