The short answer is yes, you can.
You will need to
1. Turn on the
NMEA output on the GPSMAP (RTFM)
2. Buy a serial/USB cable
3. Buy a
serial cable which fits (2) and cut the other end off
4. Connect 2
NMEA out wires to 2 of the wires in the cut off cable (- to pin 5 and + to pin 2)
5. Install the serial/USB driver which works for your operating system
6. Connect everything up and turn on the
GPS
7. Use Device Manager to figure out which com port the GPS is on (it will probably say 'prolific')
8. Go into openCPN/tools/gps and select the com port (and check that the baud rate is whatever the GPS manual says (Usually 4800)
9. If the
boat symbol turns red, you're good to go (if not, try closing and opening openCPN)
Now wasn't that easy!
Or, for about the same outlay you can buy a USB GPS receiver
Amazon.com: GlobalSat BU-353 USB GPS Navigation Receiver: GPS & Navigation