It is most probably fully functional stand alone. My HDS 8 is. If the only unit envolved, forget the NMEA stuff.

The way you want to use the unit (stand alone) you can tape the wires off and all will be fine as you will not be using them. that is the "old way" of networking two units together.

NEMA  does not have anything to do with networking. It has to do with talking with other units on your boat. Neworking for using one GPS puck and one transducer is done thru a network not NEMA. They are two seperat protocols.

If you don't plan on hooking up to a VHF radio or a fuel system or other such unit like was said earlier just tape the wires together.

Lowrance uses 3 protocols for communication between devices.

NMEA 0183 is a protocol dating back to 1983 and allows for simple message "sentences" to pass between units using an agreed protocol. Most modern electronics have outgrown this protocol. I use this to provide GPS data to my VHF for emergency location.

NMEA 2000 is an update to the previous protocol and supports a richer more versatile communication language. this is the protocol used by Lowrance and others to communicate between devices. I have added a GPS puck, gas gauge, oil gauge, temperature gauge to my existing LCX110. Future expansion will be to add an HDS unit to the same "Lowrance Network" either Red or Blue using NMEA 2000 protocol. Many engine manufactures are adding NMEA 2000 compatabilty so that engine status can also be monitored using the same network backbone. Waypoints can be passed between Lowrance units using this protocol and connection.

Lowrance Ethernet is the third communication protocol used by lowrance, this is not the ethernet familiar to computer guys. Lowrance ethernet is used to digitally transmit analogue data between devices. This allows a sonar signal to be displayed on a second unit in the same boat.  Or for SD card data based update data to be shared between machines. (Ethernet is more complex than this makes out, but this description works for simlicity)

Simple Guide

To add an electronic sensor or show digital data between devices use NMEA 2000. I.E. Show depth as a number on a second device, or add waypoints.

To show the full sonar view on a second device use Lowrance Ethernet.

To connect to your "old" VHF radio and use the location feature under DSC, use NMEA 0183

I'm not an expert, but I researched this a lot and these are my findings, I hope it helps.

http://www.lowrance.com/en/Support/Product-Support/Networks/LowranceNET-Blue/

http://www.lowrance.com/en/Support/Product-Support/Networks/LowranceNET-Red/

Ryan, for your specific application, if you are adding an external GPS you will need to use the NMEA 2000 backbone to connect the external puck to the unit. However I believe that the HDS units have internal GPS antennas so you don't need to do that unless you run into problems.