download three big tiles of map with lot of sea area and when downloaded, unzip the gmapsupp file and copy it the the Garmin directory on your sd card. Go to setup > map on the gps and enable only that map and leave the basemap will already be ebabled. enabled. Go to maps and you will be able to zoom in and see where you located on the map after satellites get a fix.
A detailed guide that will work on your Oregon 600 too
[dc rainmaker][1]
[1]: http://www.dcrainmaker.com/2013/05/download-garmin-705800810.html