On my R31, the NMEA backbone can be reached (not necessarily easily) by crawling as best you can into the cabinet under the TV in the master berth. The backbone is mounted to the inside of the hull just aft of that cabinet area. You should expect at least six to eight connections on the backbone — possibly more. The backbone is probably a good two feet or more long. If I recall correctly, on my boat, the radar is the farthest aft. So it’s the most difficult one to reach from inside that cabinet.
Another possible way to get to the connections, especially those on the aft end of the backbone, would be to pull the refrigerator. There is enough space behind and under the refrigerator for a person to basically climb into the space under the helm seat, which should provide some access to the backbone — especially the connections on the aft end of it.
Hope that helps.
Gini
Additional note: SJI Sailor posted his reply about the time I posted mine. The multiport backbone he linked to looks like a worthy upgrade. If I have reason to have to get access to the full backbone, I’ll think seriously about upgrading using the multiport option for the sake of having better connectivity that would minimize the need to have to get to the backbone.