As many have found, sasplanet or mapproxy already creates mbtiles from many sources including satellite image.
I wrote python scripts to convert to and from kap to mbtiles (http://github.com/seandepagnier/mbtiles-nautical-tools
) It makes more sense to convert mbtiles to kap. This is why I don't have much priority to support mbtiles in opencpn
, because you can just convert them to kap.
When you do, you lose transparency, and also the compression
is much worse, and random access (mbtiles are tiles very efficient) is lost
as well, as kap you must read the whole scanline.
If you convert kap to mbtiles you almost always lose data, or end up with a larger file, because mbtiles only supports specific zoom levels.