Do nautical maps exist for downloading like OSM ?

OSM is wonderfull for peapele travalling on earth. Does anybody know, where and how to find nautical maps for free downloading (e.g. the beautiful ...

Can OSM maps be copied onto a GPS

How can I copy parts of the OSM map onto my Garmin GPS? With which "Export" option? And how can it be transfered into an .img file which then is do...