What do I need for astro ?

[Benbow]

Dear all

I find I have to spend 10 days sailing in the Indian Ocean next week (I know, it’s a filthy job but someone has to do it). I have suddenly thought that it may be the opportunity to teach myself astro. It is something I have long meant to do for fun but never got round to. I have an old plastic Ebco (?) sextant that I used to use for VSA’s for distance off, but hasn’t been out of its case for years. Accuracy is not really the issue, except to reassure me that I am doing it right.

What else do I need? I presume I need to set my cheapo digital watch as accurately as I can before I leave (it should gain less than 1 second over that time and I refuse to look at a GPS for the time!) Apart from that, what sort of tables and instructions could I/should I download from the web ? I have no access to books or bookshops.

Thanks

 

[Guest]

a) Accurate timepiece with known error
b) Sextant with known errors and no parralax.
c) Set of Nories or Burtons Nautical Tables
d) Nautical Almanac with Celestial Body GHA / Dec etc. - best is Admiralty Nautical Almanac
e) Decent calculator
f) Navigation Text Book with explanation of Marc St. Helaire or Long by Chron method of sight reduction.
g) Plotting sheet

Optional and makes whole job much easier .... Air Navigation Reduction Tables for Sun and another for Selected Stars ....

Onced mastered - an art that is satisfying .......

 

[Talbot]

Easiest way to do this is the air navigation tables

You need a copy of the nautical almanac
You need Air Navigation Table Volume 1 available here
and you need Air Navigation Table Volume 2 for 0-40 degrees available here or Volume 3 for 39-89 degrees available here

Tom Cunlife's book on Celestial Navigation is a good primer

You need forms to do the work (shown in Tom's book) and apropriate plotting sheets.

If you pm me your email, I will send you appropriate forms and plotting sheets for printing out.

I would also recommend the pilot charts for the Indian Ocean available here

 

[BrianJ]

I couldn't give a better answer than SBC.... I would say however " go for it" its a great way to learn ie at sea. I once was doing a delivery from Fiji to Auckland and took the sextant... guess what. not once could I take a shot , due to cloud.
What part of the Indian Ocean are you sailing .. ( you luck [--word removed--] )
BrianJ

 

[snowleopard]

[ QUOTE ]
a) Accurate timepiece with known error
b) Sextant with known errors and no parralax.
c) Set of Nories or Burtons Nautical Tables
d) Nautical Almanac with Celestial Body GHA / Dec etc. - best is Admiralty Nautical Almanac
e) Decent calculator
f) Navigation Text Book with explanation of Marc St. Helaire or Long by Chron method of sight reduction.
g) Plotting sheet

[/ QUOTE ]
It all depends on the method you plan to use so it's worth having a read before you go, I presume from SBC's list above that he favours the Haversine Formula. It works but can be daunting for a beginner so I would vote for the air sight reduction tables (volume 2 or 3 depending on latitude, forget vol 1). With those tables and an almanac you won't need Nories or the calculator. If you go on to do the YM(O) shorebased course you'll be using the Air tables.

I believe the key to successful sight reduction is a good form to write it all down on as it leads you through the required steps. Any good textbook will have a form you can photocopy for your own use.

A Douglas Protractor makes plotting intercepts easy.

Plotting sheets can be bought in a pad from chart agents. It's perfectly possible to draw your own on the back of an old chart but a plotting sheet is easier though the scales on commercial sheets are drawn to suit ships doing many times your speed so you end up with tiny spider-like plots on a vast acreage of white!

 

[Gargleblaster]

The nautical almanac is available online. I downloaded it and copied it to a CDROM.

http://www.pangolin.co.nz/almanac.php

You can use it for a month free or pay for it - it's your choice.

The only problem is having to use a laptop to retrieve your information which can be hard in a seaway. However if you have to fly to your destination taking a laptop and CDroms saves considerably on weight.

I've always plotted using standard A4 graphpaper, and drawing my own scale based on my estimated position and the distance covered. Works for me.

I've also learnt a method using a scientific calculator [that calculates in degrees and minutes], which removes the need for sight reduction tables - but I also carry these on CDROM.

I used to have a Davis plastic sextant. But on a recent Atlantic crossing borrowed an Astro IIIB. I would never go back to a plastic sextant again.