Where does SeaMap get the data from?
SeaMap uses nautical data from the OpenSeaMap project. This nautical data is displayed on top of Google Maps.
What is OpenSeaMap?
OpenSeaMap is an open source, worldwide project to create a free nautical chart. In 2009, OpenSeaMap came into life. This free map includes beacons, buoys and other navigation aids. OpenSeaMap is a subproject of OpenStreetMap and uses its database. See this FAQ for more information about OpenSeaMap.
Can I help improve the nautical data?
Yes. At your desktop/laptop, you can edit seamarks by using the JOSM Editor with a plugin called SeaMapEditor.
Is the nautical data cached on my device?
Yes. It can be cleared at Settings > Clear cache.