NavList:

Hi Steve

You wrote

I'm not convinced on either of these points.  I believe that some sort of system-wide failure of the GNSS satellite systems, though unlikely, is worth preparing for.  (There's a separate discussion of "what constitutes failure?" that we could have; complete and long-term failure isn't the only scenario that has reprecussions)

Please do so identify those scenarios.  I'd like to see your list, if you don't mind.  The concerns already listed here are spoofing, jamming and partisl and systemic satellite failure. Elaborate on these, if you like.  What others are of concern?  

Preparing for a low probability event is reasonable.   It's just impractical to prepare for every eventuality, no matter the probability.  The consensus to date, by the illuminati here on NavList, is that the probability is fairly low and that there are other reasons for CN.  For example, as Frank indicates, because of traditional licensing requirements of the Merchant Marine.  However, Merchant marine also carry Radar SART, which is unlikely to be carried by the recreational boater.  

Brad

PS You are not alone in software accomplishments here.  Please argue your technical points without reference to your curriculum vitae.  That's a friendly word to the wise :)