Thanks to Carotio, who did not write the mod (I stand corrected), and to GreyBeard , who pointed us to it.
The download link works. I just installed it on my copy of SH3 with GWX.
Be sure to make a back-up of the default 4320_2160.raw file before overwriting it with the modded file.
The download has a single .raw file (drill down through the unzipped sub-directories) that goes into the SilentHunterIII/ data/Terrain/Maps/Map1 subdirectory. It has the same file name as the default, 4320_2160.raw
The mod works with both new and existing career files (when starting in port). I did not test it with an in-progress (at sea) saved career mission file.
The NAV MAP opens exactly like the default map at a scale of 0 - 125 KM (in the lower left of your map).
The overlay itself does not appear until you zoom out 4 times to a scale of 0 - 1750 KM or larger.
Enjoy.