Good beginners guide to celestial navigation

[bdh198]

Hi

I am going to be doing my first ocean passage in January, across the Atlantic, and I'm keen to use the opportunity to get some experience at celestial navigation. However, I am an absolute beginner in the subject and would be grateful for any suggestions for good beginner and introductory guides.

Also, apart from a sextant and a copy of Reeds Astro Navigation Tables for 2017, will I need anything else?

Thanks for any suggestions

 

[BelleSerene]

Tom Cunliffe's 'Celestian Navigation' is superbly conceived and expressed - and part of that genius is brevity.
http://www.tomcunliffe.com/product/celestial-navigation-3rd-ed/
https://www.amazon.co.uk/dp/0470666331/ref=cm_sw_r_cp_api_XD9vybA5G49Q1

You'll also need a quartz watch, set to GMT. Any cheapo quartz watch will do - they're all accurate enough.

 

[TQA]

Mary Blewitt's book has helped a lot of people find their way across oceans.

https://www.amazon.com/Celestial-Navigation-Yachtsmen-Mary-Blewitt/dp/0070059284

80 pages of clear and succinct explanations that demystifies the process of sight reduction. No extra BS just what you need to know.

 

[GHA]

http://www.backbearing.com
Handy site.
Check out youtube as well, some good tutorials on there.

 

[jdc]

I taught myself first by considering the spherical geometry and only then, actually some years after I'd started to navigate, the two books mentioned and frankly I found them muddled in approach. It is I think important to distinguish three essential elements, all quite taxing and all vital, and in my opinion the approach of the books fails in this since they assume no modern technology at all so all three have to be right or no result is possible. Instead I recommend that you aim to get a really good understanding of all by the end of the voyage but on day 1 you get useful and so encouraging results by letting a computer (or tablet, or smart-phone) do some of the low added-value tasks, at least at first.

The elements are:
1. Using a sextant at sea: bringing the object (start with the sun but progress to planets or stars after a week at sea) down to the horizon, recording the altitude and the time. Aim for less than about about 5' of angular error: an expert can get it to 1'. And then applying corrections for height of eye, parallax etc (don't worry overly: for sight taken form a small yacht's cockpit during a voyage in the N hemisphere in summer, using the sun's lower limb, the correction is always +12').

2. Work out the position of the heavenly body at the time recorded in 1. above. This is simply a lat and long but called Declination and GHA respectively. It's a right pain to do: lots of interpolations to get an accurate enough answer from the positions in the tables, and frustrating as it's just grind: no room for intelligence and the most trivial calculator does it better than any human can.

3. Now you have the altitude of the heavenly body (sun) and it's position on the surface of the earth you have to convert this to a position line. It's of course not a straight line: it must be a circle around the point where the sun is dircetly overhead, a circle such that the angle at the centre of the earth between any point on it and where the sun is directly overhead = 90 - the altitude measured at the sextant. How you use this, approximeate to a straight line on a small section of chart, use DR to make a running fix with a subsequent sight at a different time of day, how you make a plotting sheet etc is normal enough navigtional concepts and Cunliffe's book does fine.

So I suggest that step 2 is a waste of time at first. Get a computer to do it for you until 1 - which is an essential craft skill - amd 3 - which comprises standard paper and pencil navigation techniques and so is quite theraputic I find - are mastered. Blowing my own trumpet you can find such a calculator on my website, but there are loads and I don't imagine that mine is in any way the best.

Good luck and enjoy it!

http://www.awelina.co.uk/sextant/JavaScript_Sextant_calcs_2016_2.html

PS: I should have pointed out that you don't have to be on-line: you download the nav calculator and then can run it anywhere. Also that it's nearly the end of 2016 so I'll release the 2017 one v soon.

 

[Sandy]

Mary Blewitt's book has helped a lot of people find their way across oceans.

https://www.amazon.com/Celestial-Navigation-Yachtsmen-Mary-Blewitt/dp/0070059284

80 pages of clear and succinct explanations that demystifies the process of sight reduction. No extra BS just what you need to know.

Others may have a totally different view of that book. Mine is I was more confused at the end that I was at the beginning. Perhaps her style, I am sure she taught Dickens.

 

[siwhi]

Worth a look:

https://my.vanderbilt.edu/astronav/

 

[alant]

Others may have a totally different view of that book. Mine is I was more confused at the end that I was at the beginning. Perhaps her style, I am sure she taught Dickens.

+1, I find Cunliffe more user friendly for beginners.

 

[Foolish Muse]

http://www.backbearing.com
Handy site.
Check out youtube as well, some good tutorials on there.

You will find the best, simplest, most common sense, and FREE, sextant users guide right here on Backbearing.com.
http://backbearing.com/files/Sextant-Users-Guide.pdf
In fact the author gave a lecture on this topic to the local bluewater crusing group just a week ago. I know, 'cause it was me
You'll be finding yourself within an hour.

 

[Barnacle Bill]

Reeds Ocean Handbook, besides loads of other useful stuff, contains a chapter which gives complete step-by-step instructions to taking a sight and performing a sight reduction, using pencil and paper and a form (which you can download from http://www.aztecsailing.co.uk). It uses the 'concise sight reduction tables' that are contained in The Nautical Almanac.

The logic of this is that you need a copy of The Nautical Almanac anyway, so you already have this table; so there isn't much point in getting the 'Air Tables'.

The method uses pencil and paper. Sight reduction calculators are available, but if you need Astro as a fallback, say if your GPS fails, then the calculator might have failed for the same reason.

I recommend this because I wrote it, and if you want any further information you can visit http://www.aztecsailing.co.uk and/or contact me.

 

[Skylark]

I'm sure that there are many ways of learning how to take a sight and plot the resulting Position Line and to create a running fix from, for example, sun forenoon, meridian passage and afternoon sun sights. We each have our own ways of learning.

For me, I didn't find the Mary Blewit book to be any use, too oversimplified and lacking detail.

I'm a big fan of Sir Tom but, with a great deal of respect, I don't think his Ocean book is his finest work.

I liked the Adlard Coles Ocean Yachtmaster text book. I liked the logical layout and progression of each chapter and, for me, it went deep enough to give a good understanding.

Many people use Sight Reduction Templates. I like to work through systematically following my logic, not someone else's.

Just to add to the discussion, you should take 3, cheap, digital watches. One.......may be wrong. Two.......which one is right? Three.....hopefully, tow of them will be the same!

 

[Foolish Muse]

Just to add to the discussion, you should take 3, cheap, digital watches. One.......may be wrong. Two.......which one is right?

One of my boss's favorite sayings is "a man with one clock always knows what time it is. A man with two clocks never knows what time it is."

 

[bdh198]

Thanks for all the very helpful suggestions and advice. There clearly is a lot to celestial navigation that can't easily be condensed into a simple 'beginners guide'. Some of the YouTube links and maybe a read of Tom Cunliffe's book and Tim Bartlett's RYA handbook might be a good starting point. At least there will be plenty of time to practice on the crossing!

 

[dom]

....and Tim Bartlett's RYA handbook might be a good starting point. At least there will be plenty of time to practice on the crossing!

Mel now of course ...an I'm sure every bit as competent

 

[capnsensible]

Whatever you use (I like TC's book personally) the best tip I got is get stuck in on day one and do sights every day, no matter how knackered you feel. Lotsa books but practical advice is thin. Get the best plotting sheet you can fin. Stokie Woodhall has the best for me. It's pants getting some good sights and plotting them on a tiny corner of a big bit of paper.

Don't forget the moon, stars and best of all, planets (imho)!

It's a great feeling to nail your position from stuff gazillions of miles away.

Also don't forget to get a suitable tattoo after..........

 

[alant]

Whatever you use (I like TC's book personally) the best tip I got is get stuck in on day one and do sights every day, no matter how knackered you feel. Lotsa books but practical advice is thin. Get the best plotting sheet you can fin. Stokie Woodhall has the best for me. It's pants getting some good sights and plotting them on a tiny corner of a big bit of paper.

Don't forget the moon, stars and best of all, planets (imho)!

It's a great feeling to nail your position from stuff gazillions of miles away.

Also don't forget to get a suitable tattoo after..........

Tom said he's had no luck using the Moon.

 

[Buck Turgidson]

https://www.youtube.com/user/NavigationTraining/videos

Much better than bikini clad bimbos.

 

[GHA]

Thanks for all the very helpful suggestions and advice. There clearly is a lot to celestial navigation that can't easily be condensed into a simple 'beginners guide'. Some of the YouTube links and maybe a read of Tom Cunliffe's book and Tim Bartlett's RYA handbook might be a good starting point. At least there will be plenty of time to practice on the crossing!

none of the sources seemed to present a beginners overview, so here goes

You're in the middle of a sports stadium with just one floodlight and not sure where you are, so you pretend to know where you are then look in a book which will tell you the angle of the floodlight above the ground if you were there. Then you measure the angle of the floodlight for real and from that it's quite easy to work out how far from your pretend position you are, though it's on a line, you could walk around the floodlight and the angle would remain the same. That's about it, pick a pretend position near where you think you are, you can find out what angle the sun would be if you were there, measure the real angle and calc how far from the pretend position you are. The rest is just twiddling to get it accurate

 

[GHA]

You will find the best, simplest, most common sense, and FREE, sextant users guide right here on Backbearing.com.
http://backbearing.com/files/Sextant-Users-Guide.pdf
In fact the author gave a lecture on this topic to the local bluewater crusing group just a week ago. I know, 'cause it was me
You'll be finding yourself within an hour.

Wow!
single handed sailing and backbearing!

You one prolific dude in the land of useful things! !

 

[capnsensible]

Tom said he's had no luck using the Moon.

Don't have the book to hand, not on boat right now but I'm fairly sure he says people worry about it without trying. It's a problem at some times with the melon slice, but I've tried a good few times with spot on results. Practice........

Oh, and on a good full moon plus horizon, you can get a star or two if the declination is within your tables and you can reduce it using normal form. He mentions this, tried it, worked.

To boldly go.......:encouragement: