The 1824C/NT is still current product and being sold. You can buy just a display unit of this type (RDP149) for a new 10.4" location on the boat (P/n# GD1920C/NT). We have discontinued the 7" NavNet displays (RDP148) but they can normally be found on the used market. You can easily network in a new 10.4" or a used 7" into your existing 1824C/NT network. If you wanted to network in the older NavNet 1 series unit(s) like the RDP139, it can be done. The NavNet Series 1 and Vx2 can be on the same network together. They will share the Radar, sounder and NMEA type information when available. They will NOT share charts with each other over the network like two Vx2 units. Sometimes a used NN1 will fill the bill for a second station, depending on what you wish to accomplish. You should work with your dealer because it is advised to have the newest software in both series of units and ensure proper setup.