Sextant - celestial almanac?

Cardo

Cardo

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My anniversary gift this year was a sextant. I've been reading Mr Cunliffe's guide to using one of these beasties and I understand I require some kind of reference to see what the stars and whatever are doing. Bit like a tidal atlas, I guess.

So, what should I get?
 
if. like me, you prefer to touch data rather than look at it, then:-



Norie's Tables (Amazon £20)

The Nautical Almanac 2013, UKHO, or Amazon £16.80

Sight Reduction Tables for 39 to 89 degrees., Amazon £15.04


Some Sight Reduction forms, to help process your sextant and chronometer data in a logical and easy way.


Come to think of it, Bowditch's American Practical Navigator, is a must as well. :)
 
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The Commercial Almanac (as advised above) is the best (IMHO) if you want a paper one. I don't like Reeds. There are various online and PC based almanacs available (PM if you want a spreadsheet based one).

Similarly for sight reduction you either need a paper version (Standard, Air, Ageton's, etc. tables) some of which are available on line. The Commercial Almanac contains a set of concise tables that work fine. Or you need an online or PC based system. Again, many are available, some are free.

The Commercial Almanac contains the formulae necessary for creating your own process, on a PC or with a calculator.

Enjoy all the adding up... Which sextant did you get?
 
Cardo said:
I gather a computer application can do a lot of the mathematics for me?
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Have to say I don't see much point in computer-assisted astro. If you're going to let electronics do part of the work, why not go the whole hog and just use GPS?

Pete
 
Cardo said:
Thanks for the suggestions.

I gather a computer application can do a lot of the mathematics for me? There seems to be a handful of apps for iPad. Has anyone used any of these and can recommend it?

The sextant I have is this:
http://www.davisnet.com/marine/products/marine_product.asp?pnum=00011

Just a cheapie jobby to see what the fuss is all about!
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Hi Cardo, I have also just bought a Davis Mk3,very old new stock it appears to date from 1968. The instruction booklet is brilliant,apparently written to get hicksville US navy cadets doing sunsights with as little fuss as possible,so after an hour`s study of it, I feel enabled to get celestial fixes all day long. (This may be an illusion). It is free to download if you google it.
I am finding that there is almost too much information (to coin a phrase) out there, both in print and online,and would recommend the services of a guide (one of the instructors who`ve posted above would be a good start) to set you off on the right track.
Let us know how you get on. By the way I won`t be using electronics in any form apart from a stopwatch..good luck Jerry.
 
jerrytug said:
Hi Cardo, I have also just bought a Davis Mk3,very old new stock it appears to date from 1968. The instruction booklet is brilliant,apparently written to get hicksville US navy cadets doing sunsights with as little fuss as possible,so after an hour`s study of it, I feel enabled to get celestial fixes all day long. (This may be an illusion). It is free to download if you google it.
I am finding that there is almost too much information (to coin a phrase) out there, both in print and online,and would recommend the services of a guide (one of the instructors who`ve posted above would be a good start) to set you off on the right track.
Let us know how you get on. By the way I won`t be using electronics in any form apart from a stopwatch..good luck Jerry.
Click to expand...

Everyone I know who has tried to teach themself to do celestial navigation has failed to varying degress of miserableness. I recently completed 3 weekends worth of formal training and it was thoroughly worthwhile. There is lots of scope for errors if you don't get all the corrections, increments and so on right. It is difficult to teach yourself (I have tried) because you may not know what errors you are making and how to correct them. Taking the sights is, I think, and relatively speaking, the easy part. It's only once you have taken your sight or sights and put the sextant down that the actual hard work starts. I thoroughly recommend Tim Bartlett's excellent book as a support to whatever teaching or coaching you manage to access.
Good Luck.
 
KenMcCulloch said:
There is lots of scope for errors if you don't get all the corrections, increments and so on right. It is difficult to teach yourself (I have tried) because you may not know what errors you are making and how to correct them.
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Too damned true! But if you can force yourself to do it a couple of times a day for a week it will become second nature. If you can get an artificial horizon (or a bubble attachment) you can take sights in the back garden, of course - no horizon needed. That eliminates one of the greatest source of errors, which is the paperwork sliding off the chart table at the wrong moment.
 
I think the sight reduction bit can be self taught especially if you use either rapid astro or the full computed altitude and azimuth tables. I used to glaze over during the maths part with spherical trig and all that stuff, but the process of filling in the sight form and doing the addition and subtraction to get the intercept is pretty simple.

On the other hand even a few hours with a decent tutor can make a world of difference to how well you use the sextant. Book and classroom stuff just doesn't cut it
 
KenMcCulloch said:
Taking the sights is, I think, and relatively speaking, the easy part. It's only once you have taken your sight or sights and put the sextant down that the actual hard work starts. I thoroughly recommend Tim Bartlett's excellent book as a support to whatever teaching or coaching you manage to access.
Good Luck.
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I think which half of the sight taking process is the hardest depends on the person taking the sight. Some people will be more mathematically minded and will find the calculation quite logical and straight forwards. However using a sextant also involves a certian amount of patience and hand eye coordination, which some people might find comes more naturally.

Also in my opinion once you have mastered the maths, which once it has been explained to you well (either by a book or an instructor or some other method) it is quite straight forward and as the process is pretty much the same each time once you've got it right thats it really. However actually going out side with the sextant and taking a sight is more of an art and you get better at it by doing it over and over again, my first sight was several hundred miles out (even though my maths was essentially correct) now after a few years regular practice I'm now consistently with in a couple of miles of where the GPS says (which is probably where you are).

Another important thing to remember about astro is that you need an accurate time for it to work. On most boats the best timepiece is the GPS which is going to be a problem when you need the sextant for real. So it is a good idea to have a couple of watches on board and sync them with the GPS on a regular basis.

So now I've rambled on for a bit I'll actually answer the original question. There a a few different almanacs out there either online or as books. The most popular seems to be the UKHO one which only really has the bits you need for astro and not alot else. Others such as reeds have more info regarding tides etc. Soit depends what you want/need.

My personal favourite is the Browns almanac which has a lot more info on various things in it. Alot of it largely useless to the average yacht skipper, but some of it is very good and is not in the UKHO one. Things like simple instructions on how to find stars and planets for the current year, and some basic instructions on astro, and tide tables. There are also notes on ship's LSA, positions of wind turbines and platforms, lights and beacons for the uk, bouyage, colregs, and some notes on advanced navigation calculations, some of which is useful, a lot of it is interesting but not really essential. However for £20 or so extra it I think it is a good investment.
 
There are various free tables out there online-useful for practising-National Geospatial Agency in US do a good one;I also have a simple neat one which can do a simple sun and moon reduction.
www.pangolin.co.nz
-do a nice shareware one valid for up to a month free and so long as your PC still thinks its in the valid month it works for ever.
As for the Almanac the one you want is from the US Naval Observatory as I recall.Admiralty price it at £40;US Navy at about £20;Commercial edition if you look hard about £15 and The US Naval Observatory under £10.
Oh yes whatever the title its exactly the same Admiralty/US Navy co production usually printed in UK even if your copy arrives from Amazon.com in the US!
 
Sight reduction tables you can get from here..

http://msi.nga.mil/NGAPortal/MSI.po...msi_pub_detail&CCD_itemID=1&pubConstant=SRTMN

I liked these 2 books on kindle..
http://www.amazon.co.uk/Astro-Navigation-Demystified-Volume-ebook/dp/B005WQWSSY/ref=pd_sim_kinc_1

Not sure about almanacs, there used to be one which covered 6 years by Commander Jolly Longname or something, but haven't seen that recently so maybe it's gone.

The almanac tells you where the sun, moon or stars really are at any given time, then to work out where you are you pretend you are at X , put the info from X and the almanac data from when you took the sight into the correct page of the sight reduction tables and the tables will give you what the sextant should read. Then comparing that with what the sextant really reads you can calculate how far away from the pretend position you are, and what bearing.
Hope that hasn't made things worse.. :confused:

Few more hoops to jump through than that but that's sort of the gist of it.

Is it,,

Drop by for a pint if you're down this way :cool:


PS Some free almanac stuff to play with
http://www.erikdeman.de/html/sail040y.htm
 
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Conachair said:
The almanac tells you where the sun, moon or stars really are at any given time, then to work out where you are you pretend you are at X , put the info from X and the almanac data from when you took the sight into the correct page of the sight reduction tables and the tables will give you what the sextant should read. Then comparing that with what the sextant really reads you can calculate how far away from the pretend position you are, and what bearing.
Hope that hasn't made things worse.. :confused:
Click to expand...

Not at all - it was grasping that while reading Tom Cunliffe's book that turned astro from a complete unfathomable mystery to something I merely haven't learned the details of yet :)

Pete
 
Although I would not have ben able to do it myself.
I have helped people learn ASTRO by themselves. The fear of math is the first thing to overcome. Its realy not that complicated.
I learened it in a class room then found i had no clue until I was shown how on board.
In any event reading the instructions in the front of the Nautical Alminac. Or sight redution tables will explain the proccess. or just use the template and plug the numbers in.
I use norries and uk alminac.
I also use sight reduction tables for sellected stars.

As for acurate time I have a Sony Short Wave thirty years old now tune to 5000, 10000, 15000, 20000 Khz and pick up CUT signal from Denver once a day to check my watch or chronometer. keep a log of the daily error and this will give you an estimate if you miss your time signal.

I take pride in knowing. and pleasure in doing, have fun
 
prv said:
Have to say I don't see much point in computer-assisted astro. If you're going to let electronics do part of the work, why not go the whole hog and just use GPS?

Pete
Click to expand...

Couldn't agree more.

There's something extremely satisfying in taking a series of sights and reducing the Hs to a position line on a hand drawn/scaled chartlet.

The 2013 Almanac, commercial edition, is on my Christmas list and SWMBO has bought from Amazon.

I have AP3270 vol 1 to 3. I love owning books and have no time at all for this Ap baloney. Bowditch is one of my favourites. Via this forum, I've just made acquaintance with the Admiralty handbook of seamanship, vols 1 to 3. Just brilliant reading.

I'm not convinced that sight reduction qualifies as mathematics. Sums and look-up seems more appropriate. It ain't that hard!

What else is there to do on an offshore passage :D
 
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