Yes, I've understood from the beginning whatever it is 'works' in the Windows world.  But, as far as I can tell the Garmin/OSM charts are not BSB.  I've not encountered this format before.  I can't find where 
Quote:
The following chart-formats are available:
KAP non Maptech BSB/KAP 
WCI SeaClear 
PNG picture-file (frameless) 
JPR Fugawi calibration-file  
CAL TTQV  calibration-file
KMZ Keyhole Markup Language (KML zipped) import for Garmin or Google
are located.
This might be a question for the OpenCPN people about a Linux plugin to do the same thing, or a question for the OpenSeaMap folk why they are using what looks to be either propriety format, an 'un-open' format, or at least uncommon outside the Garmin world format.  Because I'm missing something crucial and might have not read the fine print that OpenSeaMap is only propriety as well... as opposed to 
http://sourceforge.net/projects/opennautical/...which is.
A plugin for BSB4 encrypted format is not likely going to happen, there is too much money to be made.