Since I don't know anything anything about the setup, I'll give an opinion.
I've had things crash/reboot for reasons I'm calling voltage drop, or slump.  Somewhere between the plates of the battery, and the little chip that flips out because a threshold hasn't been met.
It would be odd that a VHF and the like would cave the power to the point a computer would reset.  
I did have a power supply that would reset when I turned on the ignition/gauges/alternator field.  I figure that out after I had replaced nearly everything but the power supply.  But, like I said, I don't know what your situation is, and my method is 1) Do the obvious, obviously; 2) Work up the list of cheap and easy solutions until I get lucky or the options fall into to hard or expensive and I re-assess.
OpenCPN's configuration file is 
~/.opencpn/opencpn.confA quick slick may is
Code:
cp ~/.opencpn/opencpn.conf{,.bak}
which is the same as 
Code:
cp ~/.opencpn/opencpn.conf  ~/.opencpn/opencpn.bak
There are some point and click methods, but....