Thanks Larry, you are a treasure.

I think I have it straight now although I had to look carefully at the
timing of your posts since the second appeared higher in the list.

No network here. My set up is about one baby step past a pencil and a
parallel rule. The handheld GPS is wired directly to the fuse for the
depth sounder and knotlog. The GPS "Data Out" line goes directly to the
radio "Data +". The radio "Data -" goes to the ground block on the same
screw that GPS power - connects to. The radio is on a separate fuse.

It sounds like I can expect to hear the GPS talking to the radio in the
background. Would it be a good idea to put a switch in the data line near
the radio so I can silence it in conditions where I am having trouble
hearing or understanding or just don't like the noise? I would probably
leave it off most of the time as I'm only wiring this up for the cool factor
and so I will have my position handy if I ever need to call for help and
don't want to have bring the GPS in from the steering station.

The radio data lines go to a two screw terminal block. When I purchase a
back up GPS, I will probably dedicate that one to talking to the radio so I
still have position data available if the one in the cockpit mount goes
overboard.

BTW I have a ferrite core on the GPS lead. When I install the autopilot,
I'm going to avoid tying the power supply to in in the same convienient
cable run as the GPS and lead it separately with its own ferrite core.

Another question that just popped into my mind:

When flying, we were religious about making sure that all power to the
radios and instruments was turned off before starting or stopping the
engine. I use my two battery bank as a single battery (for reasons
discussed at length a couple years ago). Am I at risk of frying or
shortening the life of my simple electronic items? I've gotten away with it
for two years as have apparently many other people. Saiing involves
frequent engine starts and shut downs while navigation is in progress so a
voltage suppressor in the power supply to the instruments would be a better
solution than an avionics master switch such as I had on the aircraft.

--
Roger Long