[GPSNavX]

You can use another Keyspan adapter if USB ports are at a premium then I would go with the Keyspan 4 port model..

http://www.keyspan.com/products/usb/usa4...epage.spml


If you are handy with data wiring then the best solution would be to use a Multiplexer such as the ShipModule..

http://www.shipmodul.com/en/miniplex-lite.html

Then you can connect your GPS, AIS and instruments all to one box and feed it into your Mac over one USB and serial port. If you go this route make sure you select "Use GPS Port" in the AIS and Instruments Settings drawers.