Sextant...

[skookum]

That's a nice piece of kit Stu. I've never really navigated at all, that is made my own passages. 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 learned to sail as a teenager and made a couple of decent passages on friends' parents' boats.

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.

"all available means"

[RBEmerson]

Originally Posted by stuarth

[...]
this is my sextant, still dunno the real make, but it is from German Democratic Republic, it was extremely accurate

It's a Freiberger Trommel ("drum") Sextant - a nice piece of gear.

[alan2]

Originally Posted by skookum

That's a nice piece of kit Stu. I've never really navigated at all, that is made my own passages. 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 learned to sail as a teenager and made a couple of decent passages on friends' parents' boats.

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.

"all available means"

I expect that you might get some "odd looks", a result of your sextant, however as a since deceased friend of mine, a licensed Master, Steam and Diesel, All Tonnage, All Oceans I believe, a graduate of the U.S. Merchant Marine Academy, Kings Point was wont to note, "my sextant doesn't need electricity, or satalites. His was an old English instrument, so old that it lacked the today quite common drum micrometer. He had it checked regularly, and it was dead on, he claimed. He tried to teach me how to shoot the sun with it, however I never quite caught on to reading a vernier scale, at least not that particular one.

How did you do regarding your re-silvering project? I have been told that the more shots one takes, the better they become, which might well be true. In any event, sextant shots of celestial bodies appear not to bother the bodies shot, perhaps because the bullet holes are quite small. Don't tell me about how bad a pun that is, I already know, some things are difficult to resist.

[RBEmerson]

Take care when shooting the Sun - it shoots back.

[Stuarth44]

Originally Posted by RBEmerson

It's a Freiberger Trommel ("drum") Sextant - a nice piece of gear.

Thanks I bought it new in NZ about 1980 from Trans Pacific Marine, was just know as yacht sextant Done a circumnavigation I keep my hand in, but the local beach is no good for noon shots as the sun is over the land

[alan2]

Whomever might be interested:

Having seen a couple of references to Otis Brown's One Day Celestial Navigation, I looked it up at amazon.com. Found it there, and ordered a "used" copy (paperback) from bluecottagebooks. It was described as "used-very good", and was priced at $2.25 plus $3.99 for shipping, came to $ 6.24 in toto. Book arrived within a few days of order, and it looks NEW. If anyone had previously "read" it, they were very gentle with it.

Seems interestingly put together, reading through it now.

[alan2]

RBEmersonTake care when shooting the Sun - it shoots back.

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

Possibly so, however so far, it's missed.

[alan2]

Re Otis Brown's One Day Celestial Navigation, to date, if I understood it's text correctly, it has more than earned it's keep. It seems to have clarified for me, a point I had previously been less than clear on, less than clear hell, I flat hadn't understood it. Assuming that I now have, the clarification was easily worth $6.25, which by the way, leaves an as yet uncatelogued amount of information to be absorbed.

[Stuarth44]

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

[skookum]

How did you do regarding your re-silvering project?

I am holding on to the mirror until my budget leaves room for the shipping down to Houston Texas. The resilvering itself was quoted at less than 50 dollars US. In the mean time I had a local glazier fashion a temporary mirror out of some 5mm plate. He simply scored and broke the glass in a 5cm "circle" and the ground away until the piece fit nicely into the mirror mount. Then he scored an edge in the silvering and scraped away one half with a razor blade. To finish he sprayed laquor over the remaining silvering. It's crude, bordering on vulgar. But it's good enough to allow me to take sights with the instrument and practice until the original mirror is ready. And really, its a thousand times better that what was there when I bought it, which was a mess of brown and black corrosion on a piece of quartz ground 60 years ago.

[RBEmerson]

Originally Posted by stuarth

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

Nifty article - where'd you find it?

[ad_astra]

Originally Posted by stuarth

Does anyone use weems plath starfinder and if so what year would one use for LHA, In the up to year 2000 air sight reduction tables

I'm assuming you're talking about some variation of astronomical/nautical almanac. It depends on how accurate you wish to be. Any astronomical table will accumulate approximately 1 minute of error per year in object positions, owing to the phenomenon of precession. You would also have up to a few minutes of error from using a table from a different year within the leap year cycle. Your tables will still be good enough to measure position to within about 10 nautical miles or so (just using the year 2000 data), but if you require more accuracy, you will need a new almanac.

[RBEmerson]

For people trying to restore or otherwise "clean up" (for want of a better term) a sextant, I strongly recommend Bill Morris' self-published book
The Naked Nautical Sextant and its Intimate Anatomy

Below, with Bill's permission, are his comments on re-silvering a mirror. Please understand that the process involves the use of a strongly corrosive acid (muriatic acid, called "sprits of salt" below) and other hazardous materials. Proceed at your own risk! If you are the least bit uncertain about following the procedures below, don't do it.

Originally Posted by Bill Morris

There are several methods for silvering glass. The one to be described uses Rochelle salt and, though it is slower than the well-known Brashear method, it is much more economical of expensive silver nitrate. The main problem for the amateur is to obtain the chemicals needed, as many chemical suppliers will no longer supply individuals. Happily, most of the ones needed are easily found in hardware stores or supermarkets.


To make Rochelle salt

While Rochelle salt(potassium sodium tartrate,) can be bought, it is expensive in small quantities and is easy to make, as follows:

1) Heat 250 grams of baking soda(sodium bicarbonate) in a glass dish in an oven for an hour each at 65, 120, 175 and 230 °C. This converts it into sodium carbonate.

2) Add 100 grams of cream of tartar(potassium bitartrate) to 125 mls of water and heat in a water bath until simmering. Then carefully add the sodium carbonate little by litttle until it causes no more bubbling.

3) Filter while hot using either proper filter paper or a paper coffee filter and then evaporate the solution by gentle heating to obtain a solution of syrupy consistency. Allow it to cool, decant off the fluid and dry the crystals of Rochelle salt that form.

This gives you much more Rochelle salt than you need, but for most people it is difficult to measure and work with small quantities.


To make Solution I

1) Add 5 grams of silver nitrate to 300 mls of distilled water.

2) To this solution add strong ammonia solution(sold as a household cleaner) drop by drop until a dark brown precipitate of silver oxide forms. Continue to add drops of ammonia until the cloudiness almost clears, to leave a straw-coloured solution.

3) Add 200 mls of distilled water.


To make Solution II

1) Add 1 gram of silver nitrate to 500 mls of distilled water and bring to the boil.

2) Add 0.83 grams of Rochelle salt dissolved in a little water.
The solutions are light-sensitive and should be stored in the dark, in brown glass bottles. Many people may have difficulty in weighing such a small quantity of Rochelle salt. A level teaspoonful of the fairly coarse crystals formed as above weighs about 2.5 grams, so 0.83 grams will be about a third of this amount


To clean mirror

Absolute cleanliness is very important to success.

1) Remove paint using a proprietory paint remover.

2) Remove silver by immersing the mirror in hydrochloric acid, sold as “Spirits of salt” for etching concrete. Be careful with this acid as it rapidly burns skin and clothing. Wear rubber gloves and eye protection at least. It also fumes in damp air producing irritating, corrosive gas, so work in a well-ventilated, draughty environment, away from any precious tools or equipment.

3) Rinse in distilled water, swab with white spirit and wash with soap and water to remove all traces of grease. Wear rubber gloves to do this so that you do not add oils from the skin to the surface of the glass. Rinse again in distilled water and dry with a clean, well-washed old handkerchief.

4) Swab with alcohol(methylated spirit or isopropyl alcohol), rinse with distilled water and keep under distilled water until ready to silver.


To silver mirror

1) Remove the mirror from the water and place wet in a shallow glass dish with the surface to be silvered facing upwards.

2) Mix equal volumes of Solution I and Solution II and immediately pour the mixture over the glass. It may take an hour or more for a sufficiently thick film to deposit. Gentle warming to about body temperature may speed the process.

3) Remove the mirror, rinse with distilled water and allow it to dry in a dust-free place

4) Add some flakes of sealing wax to some alcohol to forms a varnish and paint three coats over the silver, continuing around the edges of the mirror. Alternatively, use modern acrylic paint.

DISCLAIMER: I have no connection with Bill Morris or his publishing effort, save as a customer.

[RBEmerson]

Originally Posted by ad_astra

I'm assuming you're talking about some variation of astronomical/nautical almanac.[...]

Actually... um, er, well... not quite.

Stuarth is referring to a 2102-D star finder such as this (LINK). Frankly, the darn things have always confused me no end, but for those with more patience for the 2102, there's this book (LINK).

DISCLAIMER: I have no connection with Starpath, save as a customer.

[ad_astra]

Originally Posted by RBEmerson

Actually... um, er, well... not quite.

Stuarth is referring to a 2102-D star finder such as this (LINK). Frankly, the darn things have always confused me no end, but for those with more patience for the 2102, there's this book (LINK).

DISCLAIMER: I have no connection with Starpath, save as a customer.

Ahhh.... so if I understand correctly, it's not a device for aiding in reduction of celestial nav, but a tool for figuring out where an object is on the sky? Basically a much more accurate version of this ?

If I understand the device and book correctly, then the tables should still be fine for the sun and stars , but not for the planets or moon.