Getting Mariner to show charts is a three-step (at least!) process. First, you need to point a chart browser at the sub-directory with the charts (I got my charts directly from NOAA at
LINK - the charts, when the ZIP file is expanded, are contained in BSB_ROOT so I looked in /usr/share/charts/BSB_ROOT/ ), and then you have to import them into Mariner. Once imported, you need to tell Mariner to display a chart, either by name or by position. Regrettably, none of this seems to be done "automagically".