Earl,

All marine equipment must at least meat IEC and FCC standards with regards
to unwanted emissions and susceptibility to RF emissions. On top of that,
most marine electronics manufacturers meet the IEC945 standard, which is
specifically designed for the marine environment and has, amongst others,
much lower limits on unwanted RF emissions on marine frequencies.

So to make a long story short: give each device a decent power pair and you
will have no trouble at all.
If you use screened wire for data connections (NMEA et. al), use a wire
within the cable for ground/return connections and connect the screen ONLY
ON ONE SIDE to ground. Do NOT use the screen as a return path for a signal.

When you need to use an inverter, feed that beast directly from the battery
and install filters on the input and output IF you experience problems. And
buy a decent (=expensive) one, not one of those cheap crap square wave or
modified square wave types.

As for the SSB: the only good place for the tuner is DIRECTLY at the feed
point of the antenna. If the SSB interferes with the other equipment, use
ferrite clamps on the wires to a device, as close as possible to that
device.

Meindert (marine electronics engineer).