Basecamp can't display and use pre-intalled marine chart

Hi — if this question has already been addressed in an older thread, I'd appreciate a pointer to it; I didn't see a thread title which looked promising. Here's the problem:

I recently bought a Montana 600 Marine Bundle, which includes the Bluechart G2 US charts preinstalled in the device's main memory. I also bought a 32GB micro-SD card and the City Navigator North America NT product on a CD, and have successfully gotten that map registered, on my Mac, and loaded on the micro-SD card in the Montana. However, when my device is connected to my Mac via USB, Basecamp does not show me any of the marine data, which means that I can't establish new waypoints (or define routes, etc.) on the water. (I'm primarily interested in data for Cayuga and Seneca Lakes in New York's Finger Lakes, which have full coverage for depth contours and navaids when I look at them directly from the device.) Rather, the Maps menu has entries only for the City Navigator product and for the Global Map, but not the pre-installed Bluechart product.

How do I see the Bluechart data through the BaseCamp Mac tool, so that I can create waypoints, tracks, and routes? Thanks for your help,

Paul