Sextant...

[cdennyb]

Science Store - Optical Components

look for some places like this to buy state of the art front surface silvered mirrors. Measure the one you have now using a digital micrometer set to mm and try to match or e-mail the various suppliers and you can pick one up for about $5.00 or less plus shipping. Be sure to get a front surfaced one.

[RBEmerson]

Yep, it's a form of planisphere, intended to make setting up for star shots easier. The 2102 can also be used for planets, although that takes some table work to set up.

[alan2]

Originally Posted by stuarth

save me wrting it all, may seem long at first glance, but in practice takes no time at all

Is the data included in your post # 99 the entirety of the text/article? If not, could you put the rest of it up?
Thanks.

[Stuarth44]

Thanks all nice replys
Dont get a lot of time
there are, were, two almanacs in common use, one is Norries tables But Air Sight tables are easier
Weems and Plath were American I believe you can still buy starfinder, handy for even a farmer who want to know, what and where
what is the brightest star?
Syrious the Dog Sar!!!
the article I posted was from YACHTING Nov. 1980 by Stafford Campbell, in a series called Practical Navigation. I carried it always in my sextant case, along with my hyperdeemic nurdles)

[RBEmerson]

FYI see this note posted in a separate thread here:
On-line HO249 Corrected

[alan2]

Originally Posted by RBEmerson

FYI see this note posted in a separate thread here:
On-line HO249 Corrected

-----------------------

Regarding what passes for my efforts at celestial navigation, I use the Nautical Almanac, ergo errors in Publications 249 and 229, there were some discovered in both no?, I'm unaffected.

Also, as I understood, perhaps incorrectly, the errors in 249 fell into a very narrow area, how about 229, same for those tables?

Having said that, others use these tables, and any errors therein could become troublesome, so it's good to see that responsible parties have taken action, having been apprised of situations, and the errors have been corrected. On-line users can, it seems, now download corrected versions.

[RBEmerson]

AFAIK, HO229 hasn't had the same problems that plagued HO249. There were at least two problems with HO249 and they were found throughout the tables, particularly the formatting error, which suppressed the minus sign ("-") before some table entries. It's my understanding the other problem (results apparently repeated through several pages) was computational and, therefore, possible to have an impact throughout HO249. In short, for some period, HO249, in print and on-line, was effectively "broken".

HO229 escaped all of this. AFAIK...

[Svanen]

Originally Posted by skookum

The only outstanding deficiencies on the instrument are a tarnished brass scale (which some Brasso should remedy)

I advise against using Brasso or any similar abrasive on the scale. Probably best to just let it be.

[Svanen]

Originally Posted by skookum

When I was a kid back in the 80's I spent way too much time on the bridge of my old man's minesweeper watching him make junior naval officers sweat on their nav course.

I did part of my MARS training in Chaleur in the 80s'; and yes there was considerable sweating done by all trainees!

Originally Posted by skookum

Now I have a kid of my own and I'm about to join the Navy too. Even though they stopped teaching astronav a while back, my sextant will still be coming to sea with me. Can't wait to see the looks on my fellow officers' faces when I show up on the bridge with that old relic and an armful of tables and almanacs.

Well ... do whatever you think best, but my advice would be leave it at home. You won't use it and it will just be something to get stolen or broken.

More to the point, you will come across as a pretentious weirdo (if you are less than 100% proficient with astro nav) or as a know-it-all jerk (if you are proficient). Better to just focus on learning the syllabus, which you will find to be quite challenging enough.

There is nothing wrong with doing your own thing, or cultivating one or two eccentricities; but not while you are a naval cadet / JOUT.

My two cents.

Originally Posted by stuarth

Thanks I bought it new in NZ about 1980 from Trans Pacific Marine, was just know as yacht sextant

Yes, you have a Freiberger Yacht Sextant, not the Drum Sextant which is a different model (larger, more expensive, a couple more bells and whistles). Many people prefer the Yacht Sextant because it and its case are smaller than the full size versions, hence easier to stow.

[RBEmerson]

Originally Posted by Svanen

I advise against using Brasso or any similar abrasive on the scale. Probably best to just let it be.

Agreed! As long as the scale is clean, at most put a light coat of wax on the scale and keep the instrument clean and dry!

[alan2]

Re sextant maintenance, the booklet that came with my Astra made the usual suggestions, don't drop the thing, do not bathe the instrument in sea water, and if you do, rinse well in fresh water, this sounds extreme, then dry well. Would a hair dryer work for this? Seems as if it would. Generally, keep it clean.

The booklet did make particular mention of the following. Keep the arc grooves clean and possibly apply a THIN coat of petroleum jelly or a minuscule amount of oil to the grooves and the machined slot in the bottom of the arc.

Re oiling a metal sextant, Celestaire offers what they describe as Sextant Oil. I assume that the sextant was properly lubed originally, which leaves the following question. How often to oil. Looks like the only place that might require oiling would be the index arm pivot, at the top of the sextant. I suppose one could use a small "Q Tip" to apply a bit of oil.

[Sailndive345]

Originally Posted by alan2

Re sextant maintenance, .... Would a hair dryer work for this? Seems as if it would. ....

Perhaps you ought to avoid the hair dryer approach; the heat may warp the metal just enough to cause reading errors. A soft, absorbent cloth should work suffiently well...

Fair winds!

Sailndive

[RBEmerson]

Use common sense with hair dryer, the idea is to warm things, not cook them. But coming up with power for a dryer at sea is limited. Go with lots of fresh water (salt water is bad, bad, bad!) and let it go at that. As to oiling, "less is more". Over-oiling attracts dirt, gums things up, and generally does no good. A light touch on occasion is enough.

[kefroeschner]

One small point regarding index error. As I understand things it is not necessary to look at the horizon to do this, you can look at anything at all. A star for instance, or the neighbor's ..., well anyway, the point is that when the index (hs) reads zero, the two images of whatever should be exactly superimposed. The adjustment needed to bring this about is IC. N'est-ce-pas?

[btrayfors]

Originally Posted by kefroeschner

One small point regarding index error. As I understand things it is not necessary to look at the horizon to do this, you can look at anything at all. A star for instance, or the neighbor's ..., well anyway, the point is that when the index (hs) reads zero, the two images of whatever should be exactly superimposed. The adjustment needed to bring this about is IC. N'est-ce-pas?

Not quite. You can't look at just anything. Index error is only reliably measurable when looking at superimposed images of things which are a long distance away....essentially at infinity....like a star or planet or the horizon.

Focusing on nearby objects like your neighbor's whatever will give a false reading.