How to tap an AIS transceiver

Really?

The VTS provider has said there is no way to share the raw AIS data from this unit as it is a single serial port output. 

Do not use a splitter on the antenna.  That will drop the signal strength to both the AIS transceiver and any radio you add.

This is a failure of the VTS provider to think through much of anything.

You can tap RS-232 or RS-422 and listen in on the serial.  Or you can probably tap the serial port inside the OS.  Or the app could easily do a localhost UDP broadcast of the NMEA.  Or provide a TCP localhost service providing the raw TCP. Or the app could write the raw NMEA to log files that you tail (e.g. what tail -f does).  Or setup a service that listens to the serial port and provides a connection for the VTS software so it does not talk directly to the serial port (similar to what GPSD does) Or betting that this is windows there are options I don't know because I avoid MS windows.   If the VTS provider is Transis, they know better than to say this.  Or can put a computer with two ports in between the AIS transceiver and VTS machine and do forwarding of all messages. On a linux machine, you can modify the serial driver to send the data to a 2nd location.  Or maybe fiddle with the pts setup.  Or ...

Just look through socat for more ideas!

Here is an example socat command line I used a while back with the USCG AISUser.jar:

socat -u TCP:localhost:31414 - | grep --line-buffered 'r003669945' |  socat -d -v -u - TCP4-LISTEN:35001,fork,reuseaddr

An old AntiLog device with tap: