Use of a Sextant

[BlueSkyNick]

One of YM's competitors has an article about purchase and use of a sextant. I know it is part of the YM Ocean syllabus and a few old farts on here will have been trained to use one.

But just how many boats carry a sextant, and are they ever used ? Let's find out....

 

[Stingo]

I own a sextant but don't know how to use it, but keep it for emergencies when I will learn in anger.

 

[capnsensible]

Got 2, use em. What a way of relieving boredom on a long trip. My wife, having far more patience, is adept too. Enjoy teaching the course. This is getting a bit of a pose so stopping now, but remember to learn before you go....practise safe sextant. /forums/images/graemlins/grin.gif

 

[Csail]

Slightly off the topic but it reminded me. I was chatting with a friend a few days ago and he asked me where he could get the relevant tables to use with his sextant. ( don't know exactly what he meant as i have no idea about sextants)
Any ideas?

 

[jhr]

This kind of thing?

You'll find them Here.

 

[capnsensible]

Admiraty chart agents. He will need plotting sheets, (I use IMRAYS), up to date Nautical Almanac, Sight reduction tables Vol 1 (selected stars) and for latitudes 0-40, vol2. If he is North of 40, vol 3. You can just use the method in the Almanac but its more complicated, sight reduction tables ease the problem. I like Tom Cunliffes book about Celestial Navigation not only as a good reminder, but to answer difficult questions!!

 

[Talbot]

if you pm me your email, I will send you some forms and a plotting sheet, which will assist in getting a sensible answer from your sextant work.

 

[ChrisE]

Or a Tamayra calculator...

 

[Skyva_2]

You left out:

Own a sextant, did the course but would not have a clue if called upon to use it.

Was it not Chay Blyth who set out round the world for the first time and when asked if he could use a sextant, said 'No, but I can learn as I go along!'

 

[Twister_Ken]

No category for those who once knew how to use a sextant, but have wiped it from their memories in favour of knowing which screen to look at.

 

[michael_w]

As I'm a complete mathamatical numpty, the problem I have is doing the sums, adding and averaging degrees and time I find very difficult. The actual business of sextant work isn't too hard, stars excepted.

Is there a calculator that can be set to work in any base and make my life easier?

 

[Kilter]

[ QUOTE ]

Was it not Chay Blyth who set out round the world for the first time and when asked if he could use a sextant, said 'No, but I can learn as I go along!'

[/ QUOTE ]

Worked for me! We did have gps as well though!

 

[whipper_snapper]

Bear in mind that a sextant has uses other than astro navigation. I often used to use one for distance off and (less often) for HSA's (horizontal sextant angles). Both are really neat ways of getting a very accurate fix - but I confess I haven't done one for years.

 

[Robin]

We used to carry a plastic Ebbco sextant and I used to know how to work up sights, nowadays I can see it from my desk here in the office! I still have pre-printed forms and the tables to use to work up a sight so in extremis would probably manage it as I wrote the forms in an idiot's guide kind of way to suit my own methods. However I still have a little Casio FX3 programmable calculator with the programs from way back in PBO installed, in Basic. This includes almanac data even for moon and stars that is still current. In addition I have a program (freebie from the internet somewhere) on the laptop that will also do the calculations.

Of course all of this is irrelevant without an accurate timepiece, I always used the time from GPS but if I wanted the sextant because all the GPSs failed I would be well snookered!

Also as someone else said, sextants were good for doing horizontal fixes and distance off by heights, last used as such by me when I owned a Seafix RDF.

 

[bilbobaggins]

No, this kind of thing.....

Harry Baker's is decidedly cheaper, much more compact, and easier to use on a small vessel than the hefty Air Tables. As someone who 'earned his crust' with the Air Tables for a goodly number of years, I have considerable personal experience of both to inform my view. Add in Tom Cunliffe's excellent book on Ocean Navigation, or one of a score of other excellent 'astro cookbooks', and the time to get good at it, and 'Robert's closely related to an esteemed parent'....

The RYA Ocean course does not include inter alia how to use a sextant effectively - or how to keep it 'tweaked' and accurate. It is focussed instead on how to resolve and plot a sight. One needs both sets of skills, which are closely dependent on practice and mentoring, as many will concur.

However, effective and reliable use of a sextant - a complex maritime skill - takes most peeps a long time to acquire, like reliable anchoring, sail trim, weather lore, crew management, and I'm quietly tolerant of those who proclaim "I'll read the book if I ever need to....."

Those who bother, and persevere, get considerable satisfaction from knowing that they have the skills stored away, should they ever be needed. And that's what yot mastery is about, surely.....

Enjoi!


/forums/images/graemlins/smirk.gif

 

[pyrojames]

I have one, and keep all the tables on board, but no longer buy the almanac each year. On ocean passages I would use it just to keep my eye in, so I guess I fit somewhere between the have but don't use and have and use.

 

[tome]

Last used my Zeiss sextant about 6 years ago, since when it's been consigned to a cupboard at home for when I next need it. Last time was just to keep my hand in and did a meridian-run-sun sight which came out reasonably well against gps. It's surprising how quickly it comes back

Incidentally, GPS time is very good for rating the ships clocks. Just record the time offset for each time piece against gps time in the log every few days and you'll have an excellent record in case you lose gps and have to get the sextant out

 

[Guest]

No row for :

Used one professionally, had one, no longer have one. (Brother nicked it for his collection - to join his one !)

As to those who can't do maths ... I could do it - but got fed up with the rows and columns of numbers ... so bought a Texas Ti59 and Nav Module ... still works as well ....

Someone sooner or later may mention Long by Chron or Marc st Helaire ............. then we really get going !!

 

[bilbobaggins]

I'd really like some well-informed opinion on a wee technical matter to do with star-sight planning. No, really. That's what this forum is intended for, allegedly.....

Y'see, a large part of the astro fixing I did while air-nav'ing required one to plan, shoot and plot multi-shot 'sandwich fixes' ( such as ABABABA ), with the azimuths oriented about 0º/90º Along and Across the track. AP3270 Vol 1 - 'Selected Stars' facilitates this, so the pre-planning was swift ( important in a 600-knot aircraft ) - as Sir Francis Chichester held, 'cos he wrote the book on this. Literally!

The naval tradition, I understand, was to stand around in groups taking aim at seven or more assorted stars dotted all around the horizon. Those Seaman Officers on the port wing bridge would get some of 'em, as the metal/wood/glassfibre was in the way, while those Engineer and RM Officers on the starboard wing bridge would get the rest of 'em - cloud, gunsmoke, cigar smoke and mountains permitting.

Of course, the Navigator's Yeoman would do the pre-computing of sights, lay out the sight forms and pencils, and clean up the ashtrays afterwards, while Their Lords High Panjandrums would repair to the wardroom and 'compare notes' until a consensus was reached ( The 'Least Squares' or 'First Percentile' methods - or 'Reductio Ad Absurdum' in earlier times ) and a celebratory gintonic ( 'Rumbumaccordion' in Nelson's navy ) was declared.

After all, in an unhurried age and slow-witted navy, they could always come back tomorrow to check......

That is, I'm unreliably told, is the source of today's 'Zero to Hero' practice of hordes of ZtH Ocean Yotmeister candidates assembled in 3 or 4 of the RYA Sea School boats licensed to do 'Qualifying Passages' whipping out from behind Ushant on a quiet day, rattling off a quorum of sun merpasses ( one, just one! ), adding up all the numbers and dividing by the number you first thought of, then plotting the instructor's 'Intercept' anyway. Old traditions die hard.....

But why bother with pre-computing 'a round' of seven or more sights, with all the complexities of guesstimating an MPP and editing out the two or three weak stars that were misidentified, when a really good two-star, seven-shot Sandwich Fix based on two big, fat, unmistakable First Order stars, was faster to pre-compute, faster to average and plot - and a good deal more accurate?

Or was it 'not invented here'?


/forums/images/graemlins/shocked.gif

 

[bilbobaggins]

[ QUOTE ]
Someone sooner or later may mention Long by Chron or Marc st Helaire ............. then we really get going !!

[/ QUOTE ]

No, no, Nigel! I choose the field of battle....

How about 'Astro Homing On A Single Star' or 'Gyro Compass Error-Checking by Astro in Trans-Polar Flight'....? After all, the Micronesians did more or less just that, without the sums, in their twin canoes.

He, he!


/forums/images/graemlins/laugh.gif