Using a bus bar for something like this is generally causing problems
because of the physical layout. A signal wire is supposed to have the return
wire very close, in order to radiate in the least possible way. So if the
TxD signal from the RS-232 port is going to some bus bar contraption while
the ground is going to a different place, you effectively create an magnetic
loop antenna, radiating as hell.

To prevent radiation, keep signal and return in ONE cable at all atimes.
What also helps it to limit the dV/dT of a signal, or in other words: slow
down the flanks of the signal by using a low pass filter directly on the
Sub-D9 connector of the AIS receiver. Such a filter could consist of a 47
ohm series resistor in the TxD signal line, followed by a 10nF capacitor to
the signal ground. This will surpress high frequency signals that could
interfere with an SSB or VHF set.

Meindert