30/05/2024

Astronavigation

In the Begining

I have had a love/hate relationship with Astronavigation since first looking at it in school. I studied for a Navigation 'O' Level back in the late 1970's. It has always been something I wanted to be proficient with, but was totally discouraged 'put off' due to the rather bamboozling text book, Mary Blewitt's Celestial Navigation for Yachtsmen ISBN-13 : 978-1408132128. Clearly written for a different era. I'd suggest the Jurassic age with enough spherical trigonometry to put me off geometry for life, but there has always been a little voice inside that said, 'You should really understand this stuff'.

Playing with the Subject

Over the years I've had books out of the library that I've picked up, looked at, tried to get my head round some of the language and concepts then quietly returned them to the librarian just as confused, sometimes even more so!

A Quite Night at Anchor

From time to time you sail with some amazing people. One such occasion we were sat quietly at anchor and the subject of astro came up in conversation. The skipper spent about half an hour explaining the basics and that little voice inside said, 'see I told you so – it is not that difficult'.

A few months later I was sailing with the same skipper and explained that I had a 'bad experiance' with the Blewitt book and could they recommend something that led me by the hand in very small steps. They kindly suggested David Burch's Celestial Navigation: A Complete Home Study Course ISBN-13 : 978-0914025511, one birthday present sorted.

Celestial Navigation: A Complete Home Study Course

The book arrived and a quick thumb though it and it was exactly what I needed. Step by step with worked examples and a bit at the back with all the details, the boring bits well hidden until you were ready to read and digest them. Even so it was some time before I got stuck into the book, but thankfully there was not a haversine in sight!

With the wet, miserable winter of 2023/24 I had no excuse as there was little work I could do on the boat, it being so cold and damp. I set too working my way through the chapters slowly working out in my head what I needed to do and how to do it.

I did take a look at David's YouTube Channel, but quickly left as he rambles on like an absent minded professor and is extremely frustrating to listen to! After several weeks of reading and a lot of Internet searches I found The Nautical Almanac where they post both the Nautical Almanac and Sight Reduction Tables (Pub 249). In turn that has lead to me printing out the daily pages, tables and sight reduction tables for the days and latitudes that I'm sailing in allowing me to great my own document.

The Sextant

The decision to buy a sextant was logical, I really did need one, but which one. I've played with a Davis Mark 25 for some sun sights, but my research suggested that it was not great for stars and planets. The one that a lot of diffrent sources suggested was the Celestaire Astra IIIB so I dug deep into my pockets and contacted Alice at Crews Navigation in Plymouth and ordered one.

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Astra IIIB Deluxe Sextant
Picture: Celestaire.com

My initial thoughts are that the instrument has a more solid feel that the Davis and once the boat is back in the water, June 2024, I'll need to put theory into practice. I'll mention in posts how I get on.

Given what I now know I wonder if picking up Mary Blewitt's book would be a good idea?