NavList:

This seems to be the story for a lot of us. Bowditch was sitting on the
shelf. It looked pretty darn cool. Bit of a shame it's not a better
textbook, but that was never its purpose, of course.

 

Funny thing about that, it was my textbook for 3 semesters of CelNav in college.  Unfortunately I started Celnav  when the "red" Bowditch came out.  I hurried out and bought a used 1984 Vol I & II as soon as I could. 

That's really great. Do you yourself know any other folks working in similar
circumstances (on commercial vessels) who actively practice celestial?

 

I have met very few indeed.

 

Before I forget, let's talk hardware: what model sextant do you have?

 

"Have" or "use" as they are not one in the same.  At the moment, ll I have is a WW2 aircraft sextant.  I am planning on getting a sextant when I get home to practice some lunars.  As far as using sextants, I tend to use what is on the ship.  I will take some pictures of our various navigation tools and post a link to a photo gallery for those who are interested.

Sure, and a fine adage it is! I guess what I meant was, if you're using the
GPS to get the longitude and from that calculate the exact moment of LAN to
take a latitude sight, doesn't that defeat the purpose? Presumably, a
reasonable excuse for doing celestial is to have an "independent" fix. If I
think of celestial sights as insurance against the possibility, however
unlikely, that the GPS might go wacky, then I think I would want to keep the
celestial sights "insulated" as much as possible from any GPS numbers.

 

I tend to shoot sunlines as a error check method (I very rarely shoot LAN).  I enter the GPS fix into my Nav software and then punch in the sextant Hs, time, IC, T/P etc.  It will give me an intercept which can be assumed to be error in the Celestial LOP.  As long as I'm fairly close, I decide that the GPS system is on track. If there is gross error, I shoot again to see if I can duplicate it. 

Thanks for the info on the USCG licensing requirements. That's fascinating.
You mentioned:
"Latitude by ex-meridian at lower transit of Acrux."

Yeah, that's a great one.

 

Yeah it was a good half page of number crunching.  I had very limited resources in the exam room.  I have a scientific calculator, HO 229, a 1981 Almanac (all USCG Celnav is based on 1981),  Bowditch Vol II (1981), and as much scratch paper as I can use.

Yes. Modern texts usually refer to it as a "time sight". In the 19th century
it was typically called "longitude by chronomter" but that seems a bit
ambiguous today. It's rather amazing how many vessels, especially commercial
vessels, even in the 1940s did these "pure" longitude sights. The "New
Navigation" had still not completely won out even then.

 

In a strange twist of fate, I have read very few navigational texts, and less history.  I have read most of Bowditch, some Dutton's, and then the Tables I use (HO 214, HO 229, HO 249, Bruce Starke's Lunar Tables).  Everything else I know is from instruction by navigators.  This is why I think that I am somewhat lost when people reference some other tables or use terms that I am not familiar with.

Regarding getting lat and lon by sights around noon, you wrote:
"I am going to try it using your other post's instructions and see how I
do."

There's some more detail. I had to dig up another old post for reference a
few minutes ago. Here's my first write-up on the topic from three years ago:
http://fer3.com/arc/m2.aspx?i=024178&y=200506

By the way, have you ever considered the general problem of taking a series
of Sun sights in relatively rapid succession (at an arbitrary time of day,
not necessarily around noon)? For example, suppose it's 1500 local time. If
I take ten sights over half an hour, what kind of position fix can I get?
This is a generalization of the "sights around noon" problem. There's no
easy graphical solution but it's similar in other respects.

 

Not really, in school I use to have to shoot and plot "sunlines" in sets of 3's in order to get credit for the AM or PM sunline.  I really can't be that absent from the rest of my bridge duties to try such a prolonged set of shooting.  If weather permits, I will try the around noon sight only because of the rapid change in altitude with time here in the northern tropics this time of year.  I am sure I can do a good 15 minute evolution and get a decent curve, rather then a 40 minute curve in the northern latitudes.

You wrote:
"I went to camp at the seaport in the late 80's. "

Aha, so you've been sea-going for quite a long time.

 

10 years in July as a professional, and another 5 as a cadet.

 

Did you ever get dunked by one of those little Dyer Dhows?

 

No I never capsized, but they are the slowest, least responsive, boat I've ever sailed.

 

Of course, now I can estimate your age.
Somewhere between 30 and 35? I'll guess 32. Am I close?? :-) That makes you
a bona-fide 'kid' by NavList's statistics.

 

I'm 32, so you are quite right.  I just wonder how many sights I've taken, it must number in the hundreds.  I am sure the reductions number in the thousands with all of the academic problems I faced in school and studying for the exams.  In many ways I am glad I am done with USCG deck exams.  Still I enjoy them, which is why I still shoot them.

The last summer during the 80s that I was working at Mystic Seaport
full-time was '85, when I was fresh out of college (Sue Howell was lost at
sea in the sinking of the sail-training ship Marques in June, 1985 so they
needed extra help --read "Tall Ships Down" by Dan Parrot if this story is
unfamiliar). I did navigation shows at the planetarium for the Conrad
program that year, but I guess that would have been before your time there.

 

Yes it was, I can't remember the exact years I was there.  I am thinking probably 87 and 88 but I could be mistaken. 

 

Jeremy