NavList:

Kermit,

Naturally, your answer is acceptable.  It has been so in the past and will continue to be so in the future.

At the very beginning of my investigation, I came across a youTube channel, the SV Ruby Rose.  Ruby Rose is an ocean crossing yacht, strictly for pleasure.  In one of their many illustrative discussions, the topic of what is the backup to their GPS chartplotter arose.  They stated that they have a depth of 8 GPS devices and rejected CN completely as a "purists exercise".  I then remembered that in 2016, Frank said that the backup to a GPS was another GPS.

I decided to put this to the test in the group most likely to strongly disagree with those statements.  I provided the statements, by Frank Reed and by SV Ruby Rose, into NavList circulation.  

What did this group think?  

The overwhelming response is that this group does not, in fact, see CN as a practical, common sense backup to GPS/GNSS.  

Some others have argued that over reliance, strictly on GPS is single point of failure and some ( Bob Gothe for one) like you, have argued that it does remain a backup, when all else fails.  In that, there is no dispute, when all else fails, it is so.  I struggle to find the circumstance that completely eliminates GPS for a long enough period of time to make CN relevant.  Yes, we can always develop some distantly probable circumstance that requires that, at last, we must rely upon the sextant and CN.  But in absolute terms, you are correct.  When all else fails.

We should be careful not to project CN as general purpose backup.  As Francis states, his grandchildren doesn't believe it, nor does he.  Frank is correct when he states the product quality from a GPS receiver is orders of magnitude more accurate and at orders of magnitude higher frequency.  In general, when your chart plotter goes down, just get another GPS receiver.  Jeremy does just that on his commercial, ocean going vessel.  Yes, he practices CN but I wonder if the corporation would permit him to navigate the vessel that way instead of GPS, except in dire extremis.  

Is CN a Hail Mary, when all else fails backup?  Yes.  Is CN a general pupose backup instead of just another GPS receiver?  [I will halt here.  Let others carry it forward if they wish!]

Brad

On Tue, Oct 2, 2018, 1:19 PM Antoine Couëtte <NoReply_Couette@fer3.com> wrote:

Dear Brad,

Thank you for your detailed reply referenced on top of the list.

John D. Howard and Robert VanderPol II have since expressed their personal views. I am totally endorsing them and they seem comprehensive by themselves.

Most importantly and to make CelNav-DR a fully independent and last resort back-up of the back-ups, it is quite important to find ways of keeping accurate Time on-board for extended periods of time and at reasonable cost and in a practical way.

Hence the current conversations between yourself Brad, Robert VanderPol II, Francis Upchurch and others are extremely interesting in this respect.

May I suggest that the topic of "Maintaining self contained UTC on board" could be the title of a new series of dedicated posts devoted to accurately maintaining a sufficient Knowledge of UT1 onboard should UTC/UT1 broadcasting fail for some extended periods of time ? If you can keep onboard an affordable device which does not drift by more than 0.1 s / month relatively to UTC, that would be a wonderful tool. In this case CelNav/DR would be an extraordinary un-defeatable back up [of the backups] worldwide Navigation system. Such very stable UTC clock should give more than adequate time to rejoin a known spot and update it through a Celnav Fix from a known position. Food for thought to many Members here ...

Let us not forget either that Lunars can derive UT to +/- 30 seconds of time under normal conditions. This is far from being mirific but knowing one's Longitude to +/- 8' still makes landfall a reasonable exercise provided your exercise sufficient caution and judgement.

A last and non-essential point - far from being a rationale per se - is that [hand-held] electronic personal devices make CelNav much more "fun" than it used to be. This has also been pointed out by Hewitt Schlereth in "Susceptibility-GPS-CME-Rationale-for-CN-Schlereth-oct-2018-g42957", by Francis upchurch in "Susceptibility-GPS-CME-Rationale-for-CN-Upchurch-oct-2018-g42961" . Nonetheless should such electronic tools fail, it is a must to be able to tackle CelNav with tables, paper and pencil, and even starfinder. Many different "manual" methods are available as parts of "Emergency Celnav toolkits" earlier descriptions in NavList posts. Greg Rudzinski and others are extraordinary wizards in this area.

Dear Brad, I fully trust that my lateral thinking reply is not exactly up to your strong expectations. Unlike "planet phase correction" or others subjects, this current topic is not a scientific one.

It can and should accept multiple answers. Would you not agree now ?

Very Best Regards,

Antoine M. "Kermit" Couëtte