celestial navigation

[TiggerToo]

complete beginner here...

I understand that one needs tables from a "nautical almanac" or something like this. Is this publication that needs tobe accessed every year (like tidal tables) or can it be bought once and for all? i.e. do they go "out of date"?

 

[stephenh]

You need:

Nautical Almanac
the current year's , which rather like tide tables only lasts for 1 year,

Sight Reduction Tables
These come in various shapes and sizes. The simplest ( recommended) are the Air Navigation Tables (Admiralty AP 3270) Vols 1 & 2, they last forever, vol 3 lasts for 5 years and then needs replacing.

NP 401 is a bit more accurate ( possibly too accurate?) - heavy, bulky, expensive - for the enthusiast.

The USA and the Admiralty publish both together, the USA almanac and tables ( Pub 249) are cheaper , smaller and to be recommended. I tend to buy mine at boat shows .
Good luck

 

[Hephzibah]

No. One off purchase. I use Burtons tables and I got them in 1959.
Good luck with the black art!

 

[stephenh]

the black art....

Having taken timed sights with your sextant you now have to 'reduce' the sights to a useable result.

There are many ways of doing this.
As above you can have one book of tables that is a one off e.g. Burtons - I use Nories , however this is pretty 19th century and involves complex ( for me at least) mathematics, the Haversine formula, logarithms etc. There is plenty of room for plenty of errors.
You can now have this programmed into a calculator and away you go...

AP 3270 ( US 249) are called 'Rapid Sight Reduction Tables' and are as they say. If you want to be free of electronics then these are the ones to get.

Even if you plump for Burtons / Nories you will still need the current years Nautical Almanac.

Good luck and welcome to the really dark side...taking sextants through airports is a lesson in itself these days .......

 

[snowleopard]

I have an old DOS-based program that generates pages from the Nautical Almanac so I print off the dates I need rather than shelling out for the book which is pricey. I imagine there are still such programs around though most of the astro freeware does the complete sight reduction for you which is fine if you can be sure your PC will continue to function after your GPS has packed up, also you can't use a computer to work out your sights for the YM Ocean exam.

 

[savageseadog]

Have a look at web page There is a very compact sight reduction table called Agetons that is a free download. There is a very compact almanac for the sun as well.

 

[sticky]

I have produced forms for each sight which spell out step-by-step the sequence of calculations you have to follow to finish up with a position line. If you would like copies, pm me. A contribution to Help for Heroes (charity raising money for servicemen wounded on operations) would be appreciated in return.

 

[stephenh]

thanks for that ....

 

[barnaclephill]

I use "the complete on-board Celestial Navigator" by George Bennet, 2007-2011 edition. $50 Australian. All the tables inclusive, takes about 10 minutes to work out the sights yesterday.

There are other books, even books with perpetual tables, check your local nautical bookstore.

 

[roly_voya]

I am just learning to and founf Tom Cunliffes' book Ocean Sailing really good and simple - only £10 odd from Amazon

 

[Dyflin]

Do yourself a favour and have a look at Bowditch (entire book available to download here: http://www.irbs.com/bowditch/ )

 

[JayBee]

I agree. As an ex-professsional with an ongoing interest in sight reduction, particularly compact, non-electronic methods, George Bennet's book is excellent. Most short method tables need the ability to apply rather a lot of rules and can take just about as long to reduce a sight as the cosine haversine formula. The inspection tables (AP 3270/HO 249) are also excellent, but they are very bulky and unhandy on a yacht's chart table.
The Complete On Board Celestial Navigator is both long term almanac and sight reduction tables. Saw a copy in Borders yesterday. Highly recommended - no commercial interest etc