NavList:

----- Original Message -----

From: Frank Reed

To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM

Sent: Saturday, January 24, 2004 3:36 PM

Subject: Re: Latitude AND Longitude by Noon Sun

Joel J wrote:
"Within the time constraints that Frank select 20 m, we all agree that you don't need reference to tables to calculate lat [did you mean lon here?]. See below JHJ  However, it was previously stated by George, and Bill, that it is far more accurate to select times of equal altitude that are separated by an hour or more, to which I also agree. But in that case, would you not have to use tables to estimate lat [lon?] because the azimuth of the body changes so rapidly as it approaches and passes Meridian Passage?"

I'm not quite sure what you're getting at here. Could you elaborate? I thought these two sights were taken to get the average of their altitude, and than after figuring lat, calculate the time of LAN by converting arc to time. However, shouldn't the distance of their intercept prove out your DR and allow you to estimate both lat and lon at the time of the first and second sight using tables? For most of us who are not well grounded in astronomy, that unless you used tables and plotted their LOP's, that these sights standing alone would have little value except as to mathematically calculate lat. JHJ

And wrote:
"The reason I mention this is because I was surprised to find how many people are buying new and used sextants today, and the remarkable interest that is in evidence. Unfortunately, I don't know which category that Frank mentions these people fit."

There is another category of sextant owners which I do not consider to imply survival of celestial navigation. They are people who buy sextants for non-navigational reasons -- perhaps they think a sextant would impress their friends... or they've always "wanted" a sextant (maybe because 'dad had one') but they'll never do anything with it... or they are under the impression that a boater is "supposed" to have a sextant and, what the heck, it's only a thousand dollars... or it's a gift from a spouse for the boater who already owns every other toy. In effect, sextants are the ultimate "nautical jewelry" ..or "boater bling bling" to be 'muy' trendy. But the trendoids can be converted.

I've encountered many people who own sextants for reasons that even they cannot fully explain, and many would like to learn a really basic form of celestial navigation. For them latitude by Noon Sun might satisfy their limited ambitions. They can learn that technique in an afternoon and graduate from "sextant owner" to "novice celestial navigator", at least in their own minds. Adding in longitude by Noon Sun would give them something considerably more useful and take very little more time.

Most everyone in this group knows that there were many years in Navigation history where navigators practiced solely Latitude Sailings, ie they first sailed to the lat of their destination, and then turned east or west to arrive there. Its worth repeating to emphasize Frank's point. JHJ.

And Joel J wrote:
"When I was using CELNAV for passagemaking, most of my work was done at morning or evening twilight where, weather permitting, you could get solid fixes. Yes, we did do MP of Sun"

And this ties in nicely with the discussion we were having about "Old Nav v. New Nav". If you missed that, it's in the list archives and still fresh enough to join in. Noon Sun is really an "Old Nav" method, but because of its simplicity and the fact that it requires only a page or two of information instead of several pounds of tables and almanac, it may have a future that outlasts the "New Nav" that dominated the greater part of the 20th century.

And wrote:
"The other thing to consider is just what level of accuracy do you need? You're far removed from land, and barring any hazards, what difference does it make if your EP is 5 NM off?"

Exactly. And when would it come up? Celestial navigation is no longer necessary unless there is a serious emergency (complete breakdown of all electronics, disruption of the entire GPS satellite network). Under those emergency circumstances, a boater would be doing very well if he or she could get latitude to within 3 or 4 miles and longitude to within 20 or 30 miles. This level of accuracy could get you home safely and even allow one to set out across oceans without serious risk. This accuracy can be achieved easily with a set of sights lasting 15 or 20 minutes around local noon followed by five minutes of calculation. And once taught how to do it once, I would bet that a very large number of people could re-learn it from simple instructions when the need to use it actually arose (ok, that adds one more page of paper to the method, but I think it still beats an almanac plus sight reduction tables!).

 

I have maintained that to consider yourself a seaman, in this day and age, that you at least should know how to determine lat based on MP. I  was very disappointed when I went on a DV cruise on board USS XXXXX XXXXX, a Spruance, two Summers ago, and couldn't get anyone to do any CELNAV. Otherwise it was a great experience after so many years, and I was suitably impressed by many things. At our USNA, only one semester is spent on CELNAV. And a couple of years ago they wanted to drop it entirely, but the hue and cry of the alumni assoc, caused them to rescind their decision.  I also have a personal conviction, that if there was a GPS failure that the majority of the ships at sea would not be able to make port without assistance. JHJ

Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois