If your NMEA 0183 Listener is not showing any data when connected to the NMEA 0183 output of an NGW-1, the first step for fault finding should be to see if the NGW-1 supports the conversions you need.
As NMEA 2000 continues to grow, an NMEA 0183 equivalent isn't always available. I can tell you that in the latest version of NMEA 0183 released in June 2012, there are 148 sentences with between 550 & 570 data fields. In total contrast, in the latest version of NMEA 2000 released in February 2015, there are 163 PGN messages and 1569 data fields.
This article details which conversions are supported by the NGW-1:
After finding out that the conversions you need ARE supported
The next step is to find out if the NGW-1 is generating the required data.
This video will show you how to do that using NMEA Reader which can be downloaded using this link:
If the required NMEA 0183 data IS being sent by the NGW-1
The next step is to check the wiring connections and ensure the baud rates between the two devices are the same.
NGW-1 wiring instructions can be found in this article:
You will know what baud rate the NGW-1 is operating at when you successfully open the COM port in NMEA Reader (explained in the above video). Ensure your NMEA 0183 Listener uses the same baud rate.
If you need to change the NGW-1 baud rate, refer to this article:
If the required NMEA 0183 data IS NOT being sent by the NGW-1
A closer look needs to be taken at the data that is available to the NGW-1 on the NMEA 2000 network. Do that you will need to repeat the steps in the above video using an Actisense NGT-1: http://www.actisense.com/product/nmea-2000-to-pc-interface-ngt-1/
This article explains the differences between the NGW-1 and the NGT-1: