Sextant shortage

[bilbobaggins]

Which brings us neatly back to the subject of the first post. A shortage of Sextants

I believe the hobbit has at least 3 and may be increasing his collection as we speak. Are we to see a repeat of the 1637 Dutch Tulip Bubble ? will ordinary folk be priced out of the market for sextants. Will pirates charge around the channel demanding "your sextant or your life". Qucik buy a sextant they are going up in price every week.

BB what have you started

Pete

Hah! Confounded! 'Sextant futures', indeed!

You're not wrong. I DO have a modest collection of the things - which will surprise my old navigation tutor, who despaired of me, but I did survive - which at one time recently included an Ebbco 'plastic fantastic' which I'd had man-and-boy, a quietly-beautiful RAF 'flying boat' marine sextant ( I had to give that back to HM Queen ), a fine F. Smith of Southampton ( Tamaya rebadge ) instrument I acquired second-hand from a marine curio shop in Hamble village ( the guy knew what it was, didn't want to part with it, but his wife insisted he was in business to sell the stuff in his window ), an Astro 3B thing given to me by the Patron of the RYA who indicated she'd like to have it if I lost interest ( she has a way with words! ), and a Wellington bomber's periscopic bubble sextant such as I learned on some many decades ago ( it's of no use on the water; it was destined for the skip ).

Several forumeers have had some input from me on this stuff - some of it, I hope, useful. That's the point, IMHO, of this place. Peeps can come on here and ask. Some of us have something to contribute.....

Especially VO5.

 

[grumpy_o_g]

Perhaps worh noting, though, that the fallback options for aircraft are also electronic: inertial systems for "navigation" and VOR/DME for "pilotage". I am pretty sure that 747s don't carry sextants or crew who could use them.

Being pedantic not strictly true, the ultimate fall-back is a half mil (or bigger) chart, an ASI, and Altimeter, a Compass, an upper winds forecast and a TAS calculator.

Some pilots have even claimed to look out of the window and recognise things on the ground, though I think they're pushing it a bit if they expect us to believe that.

Being really, really pedantic the first 747's did indeed carry sextants, or at least the capacity to use them. Some very sophisticated military aircraft still have "celestial navigation capability" (this is American for a periscope port or astrodome) and I will risk the wrath of the NSA and CIA by telling you that a 1950's vintage periscopic sextant can be used on an E3-A. I know this because I got arrested trying to taking a photo of it sticking out, when we parked a Shack alongside one at Keflavik quite a long time ago...

 

[srm]

Bilbo, you're probably the chap to answer a question that's puzzled me ever since I discovered the bubble sextant. Why aren't all sextants bubble sextants? Surely it's easier and more reliable to use the bubble than trying to find a horizon in poor visibility?

I am absolutely useless with any sextant except, for some reason, a periscope sextant - a skill of limited use on most boats but I'm not sure if I'd want to lose the whole arcane "black arts" thing around it and I love the idea of a beautifully made piece of engineering - the good ones are things of beauty.

I'd have thought that someone would have incorporated a chronometer and electronic tables into one by now though, possibly even a star guide of some kind guiding you to the right celestial body. It shouldn't be that difficult to make it so the only input required is approx position and type of shot being taken and then press a button to log the time of the shot. It could even guide you through running shots.

Bilbo is the man to tell you about bubble sextants, although I do have one.

The basic mariners sextant though is much easier to make and to use. It can also be used to measure horizontal, slope and vertical angles. Slope angles having been used in the lunar method for obtaining time and thus longitude. Horizontal angles when coasting will give accurate positions so you can check your GPS ))

To answer a couple of your other points:

There was an attempt to produce a sextant with an electronic readout, though this was for hydrographic surveying. (I used to take a couple of hundred horizontal angles or more in a day) However, this line of development was overtaken by the introduction of microwave ranging instruments at around the same time.

Air Nav Star tables can give you the approx altitude and bearing of the celestial body from your DR position. For those who calculate from formula normal practice is to pre calculate for time and DR to get azimuth and elevation of a star. Set the angle on the sextant and point in the right direction, and you will see the star. (One reason for big mirrors mentioned in my earlier post). This works even if you don't know one constelation from another.

Hope this helps.

 

[bilbobaggins]

There are several misconceptions here - including myself, I heard someone mutter.

Nevertheless, I freely here admit that there are many, many better qualified then I to expound on the pinnacle of achievement of air navigation - air astro! I had some of the skills and understanding dinned into me by REAL experts. And I remember just some of that....

But here goes:

Why aren't all sextants bubble sextants?

The bubble bounces around too much to be really usable on a boat at sea. Those consummate navigators Sir Francis Chichester and Michael Richey tried 'em with every support-device they could contrive. They failed.

In the marginally more stable upper air, bubble sextants worked sufficiently well on most occasions. I was trained, partly, doing 1000nm flights on Varsitys using 'sun guns'. The reality was that one needed to be much higher, in undisturbed air above the tropopause ( ~ 35000 feet ), which is where the Vulcans, B-52s and Tu-95 Bears flew. Each of those trained to go to war using astro, 'cos they couldn't afford to radiate anything. We used a 'pendulous reference' periscopic sextant ( artificial horizon ) and you wouldn't believe the precision we could achieve. Certainly the Yanks couldn't work out how, even after it had been explained to them. The Russkies simply found it 'challenging'.

I shouldn't tell you this, but.... our nuclear attack submarines have a requirement to 'prove' their lair positions. One accepted means is still an astro fix, and many sub's navigators still use that as a viable means of 'proving' that the Ships INS is valid. High precision astro.

As for incorporating a chronometer and ephemerides almanac into the 'sun gun', that's been tried. Cassens and Plath were involved, AIR. It worked. It was damned expensive to maintain. You need a serviceable B-52 with the 'star tracker' fit to make it work for you..... I'm quite reliably informed that the SR-71 and the B-1 had the same system installed, as 'reversionary kit'. Certainly Air Force One has it today.

the navigation appeared to be entirely conducted on a laptop. I'm not sure how this was done as the operation was veiled in secrecy, but after a few days out, the navigator suddenly produced a sextant.... Unfortunately I did not have the pleasure of receiving an answer.

'Parsifal' had clearly encountered the dilemma of all lower deck crew - the 'mushroom club'. Get over it. Your navigator made landfall and you got home again, didn't you? Did you try 'persuading' him with good single malt or decent rum?

Some pilots have even claimed to look out of the window and recognise things on the ground

You would be surprised. I certainly was... There are many regions of the world where ICAO-approved electronic nav-aids just don't appear. Pro navigators need to be able to turn their hands to ALL the possible techniques, including the old ones of physical 'observation'. Pinpoints, transits, observed LOPs all appear in the toolbag, and are used. The periscopic sextant, depressed, can do that. It's routine.

The old AEW Shackletons used to get airborne out of St Mawgan, go SW for 8 hours at ~140 knots, then be on anti-submarine patrol for 6-8 hours, land and refuel in the Azores, then reciprocate that on the way back - all on Manual Deduced Reckoning and 3-Drift Winds. If there was a moon, then moon shots; sun, then sun shots; Plaeides - yes, please! They were the boys! Our guys were then the best in the world - tested in recurring NATO Navigation and Bombing competitions ( and we knew a bit about the Russkie capabilities ) - and all that skill just evaporated in the late 70s.

We are - if we wish to be - the inheritors of that superb tradition.

The coast of Northern Spain was my chance to test my navigation, after 36 hrs 250nm without gps (three failed) we closed (10nm) some high cliffs and only had a single lighthouse appearing occasionaly through the low cloud, the sextant and hand bearing compass gave me an accurate fix in a matter of minutes.

Neil_Y has the right approach to 'All-aids navigation'. He's a navigator....

 

[ninky]

You need to have the complete kit for it which is:~

A really good sextant, preferably fitted with light to read the arc.
Two mechanical stop watches for day use.
Two luminous stop watches for night use.
A chronometer. Mechanical or Elrectronic.
A copy of Nories or Burtons.
The Admiralty Almanack for the current year.
Foolscap paper.

Thanks VO5 (are you named after the shampoo?). Also I was very impressed with your yachtmaster description. Unfortunately, if the training is dumbed down, this limits those of us who want to learn to do things properly. I'd rather fail an exam than get through one that is substandard. Substandard exams allow substandard training and teachers (and I'd rather not pay my hard earned cash for that). Really you should not have to 'ask around' for which are the good sailing schools and courses, they should all be good if the RYA is doing the job properly.

 

[ninky]

Lat by Mer Alt of stars and planets is easy and takes say 10 mins.
Lat by Polaris is a doddle and takes ene less than that.
Noon fix depends on period of observation before and after the correct altitude is acertained, because it may involve plotting using a graph.
Ex mer is more extended and takes a fraction longer.
Long by chron takes 15 minutes or so
Long by sunrise and sunset takes 5 mins at the most.
all of these times are affected by how easy or difficult the interpolation may turn out to be.
Azimuths again are not difficult but again the interpolation is the part that needs particular care.
It is all a matter of practice. The more the art is practised the easier it is.
If it is not practised then it can go rusty.
The fear of it going rusty is probably what stimulates skilled navigators not to let go and just turn to electronics.
What you describe is a rusty navigator struggling to recover his lost art in the face of a failed electronic system.

many thanks VO5. this is all a bit of a foreign language to me but i'm glad there are still people like you to speak it and maybe keep some of this knowledge going

 

[ninky]

as mike perlham prepares to "go astro" joining the mutiny on the bounty voyage i predict there will be a new generation of sailors attempting challenges without modern instumentation and possibly engines. there's only so fast, young, round the world you can go before new adventures need to be found. and the anti-electronics approach would fit perfectly with the zeitgeist for carbon friendly activities.

certainly, it's this type of sailing that inspires me most.

 

[Mark-1]

as mike perlham prepares to "go astro" joining the mutiny on the bounty voyage i predict there will be a new generation of sailors attempting challenges without modern instumentation and possibly engines. there's only so fast, young, round the world you can go before new adventures need to be found. and the anti-electronics approach would fit perfectly with the zeitgeist for carbon friendly activities.

certainly, it's this type of sailing that inspires me most.

You may have seen this - if not you'll like it:
http://www.furledsails.com/article.php3?article=774
http://www.furledsails.com/article.php3?article=775
http://www.globestar.org/

 

[ninky]

You may have seen this - if not you'll like it:
http://www.furledsails.com/article.php3?article=774
http://www.furledsails.com/article.php3?article=775
http://www.globestar.org/

wow! what an amazing guy. many thanks for these links. i'd never heard of him before and now i want to read the book. the fact he held his dream for so many years before fulfilling it is incredible too. there is hope for me!

 

[BlueSkyNick]

I take delight in the sheer mastery of being able to navigate by celestial observation out of sight of land by day and by night.

Sorry, only just come back to this thread due to real life activities.

Taking delight in the sheer mastery is obviously an enjoyable past time, I have no problem with that. But it doesnt mean the YM course is diminished by it being taken out of the syllabus.

I was trained to locate faults to within 3 miles in submarine cables over 2000 miles long, using a 50 year old light beam galvanometer. Also to identify which thermionic valve was faulty in a repeater thousands of feet below sea level. All very interesting and useful stuff at the time, but technology and life has moved in leaps and bounds since then.

Yes it would be fun to have the chance again, but I am not treating with disdain all the bright young engineers who can now click a mouse a few times to do all the work for them, and wouldn't know what on earth I am talking about.

Apologies if you are one of the majority who havent got a clue what I am talking about.

 

[bilbobaggins]

Taking delight in the sheer mastery is obviously an enjoyable past time, I have no problem with that. But it doesn't mean the YM course is diminished by it being taken out of the syllabus.

From a not-inconsiderable experience, I disagree. As I wrote above...

Pro navigators need to be able to turn their hands to ALL the possible techniques

That is equally true of pro Yachtmasters. Those who purport to take others onto the sea 'Commercially' need to bring all the skills, judgement, seamanship and subject-knowledge to the job that they can. Opting out of a large segment of what other marine professionals consider an important knowledge-base, because it demands time and a meticulous approach, is simply 'short-changing' the clients. Trading as a professional confers a far higher 'duty of care' than an amateur's simply messing about in boats. That professional requires, IMHO, a corresponding high skills and knowledge inventory.

One might have more respect for the point of view quoted above if the individual had acquired some mastery of astro skills, and had actually used them to navigate a yacht on a 'blue water' passage. Otherwise, it's simply an opinion - and an ill-informed, inexperienced one at that.

 

[dvideohd]

you should be so lucky....

My mother-in-law gave me an Astrolobe for Christmas one year... complete with book on how to use it.. history and so forth.... also a basic sailing dingy model - with sails...

Next year - it was a "display quality Sextant.." with manual on how to use it... Along with a couple of "more" small sail boat models... you know... the ones you can learn sail trim with... and to practice on a table top....

Not long after - we got our first real sail boat - and now the back yard is more of a marina.... We built the "boat shed" this summer....

I miss my mother-in-law dearly and any here would be proud to have had her in my place...

Now, I mumble a lot as I learn with the Astra IIIB now, and I also spent a while designing electronics for the Sky Scout.

I think you can start simply and just keep growing as you learn this stuff..... It's a LOT MORE than just basic navigation...

******************

FWIW - many years ago - the advice I heard given to "would be Gold Diggers" was to take Celestial Navigation... perhaps the RYA did not know of this advice... :>

--jerry

 

[snowleopard]

One might have more respect for the point of view quoted above if the individual had acquired some mastery of astro skills, and had actually used them to navigate a yacht on a 'blue water' passage. Otherwise, it's simply an opinion - and an ill-informed, inexperienced one at that.

So to a more practical question....

Is it seamanlike to put out for an ocean passage with only GPS as a means of navigation? I have often heard people expressing the view that the only backup you need for a GPS is another GPS (or two more). Personally I would never go across an ocean without a sextant and a set of up-to-date tables.

I once shipped as navigator on a Cowes-St Malo race. The young crew of foredeck gorillas thought the sextant box I brought aboard was a great joke but when we were off the Casquets with total electrical failure and I was able to use a sun position line to get us to the finish they changed their tune. Without that we'd have been approaching a rocky lee shore on DR.

 

[30boat]

So to a more practical question....

Is it seamanlike to put out for an ocean passage with only GPS as a means of navigation? I have often heard people expressing the view that the only backup you need for a GPS is another GPS (or two more). Personally I would never go across an ocean without a sextant and a set of up-to-date tables.

I always take my sextant almanac and tables with me everytime I go offshore.It would be foolish not tnce I had a leak into the electrical panel and I had to keep drying the area with tissue every half hour.Very nearly lost all power and the sextant would have saved the day.

 

[dolphin]

Sight Reduction Tables for Marine Navigation

http://www.nga.mil/portal/site/mari...i_baseMenuID=e106a3b5e50edce1fec24fd73927a759

maybe the above link, will be usefull for someone, which like to learn how to fix a position line or find the compass error !

to fix a position using the stars/sun you need to have an almanach, sight reduction tables, correct time and of course sextant! for more reliable position, it is better to plot 5-7 lines!
once you are used to it, this can take about 30 min from start to finish!
if used air navigation table or calculator, the time can be slightly reduced !
before to commence, need to prepare an info for stars to be used (star finder) - approximate azimut and altitude for each star !
it will be nice a man to have a little knowledge for latitude, declination, LHA, azumut, celestial horizont not compulsory but, how to correct the observed star's/ sun's altitude is an obligatory !

the theory can be difficult, as use a lot of trigonometry, but the use of tables only looks !

hope this help
regards


www.neatcss.com

 

[BlueSkyNick]

From a not-inconsiderable experience, I disagree. As I wrote above...



That is equally true of pro Yachtmasters. Those who purport to take others onto the sea 'Commercially' need to bring all the skills, judgement, seamanship and subject-knowledge to the job that they can. Opting out of a large segment of what other marine professionals consider an important knowledge-base, because it demands time and a meticulous approach, is simply 'short-changing' the clients. Trading as a professional confers a far higher 'duty of care' than an amateur's simply messing about in boats. That professional requires, IMHO, a corresponding high skills and knowledge inventory.

One might have more respect for the point of view quoted above if the individual had acquired some mastery of astro skills, and had actually used them to navigate a yacht on a 'blue water' passage. Otherwise, it's simply an opinion - and an ill-informed, inexperienced one at that.

Thanks for the lecture. You are entitled to disagree with me as much as I am entitled to disagree with you, so that's fair enough. You have used words and phrases such as 'what others consider' and 'IMHO' which are themselves subjective views and nothing more.

For the record, I have every intention of learning astro-nav, in due course. This is more of a matter of interest than a matter of need, so I am all for some form of provision of training, but there are also other priorities in life.

Furthermore, I respect those with greater knowledge and experience than mine, to the extent that I was grateful to draw upon yours for a Biscay crossing. Knowing one's own limitations and working to them is a valuable skill in itself.

What I cannot respect is the arrogance of those who say that because they learned something 30+ years ago, and can still use that skill, implies that they are a more clever or intelligent person than those who are at an earlier stage of their learning curve. And that because certain aspects have been removed from a syllabus, that those who now go through it will be 'dumbed down'. There are equally, more and less capable people with less mileage in their log and years of age.

From the RYA's perspective, if new material is added to courses then something else has to be left out otherwise the duration would need to increase.

There are limits to what one can do professionally, based on qualifications, medical assessment, and category of boat. So it is not necessarily true that somebody with a 'shiny new YM with commercial endorsement' can take off across the ocean with other people's lives in his or her care.

It's time for a reality check and to keep things in perspective - I'm off to do something useful, now.

 

[bilbobaggins]

I refer gentle readers to my '#29' post above, and move on....

 

[BlueSkyNick]

I refer gentle readers to my '#29' post above,

There in lies your problem.

....and move on....

Me too.

 

[VO5]

http://www.nga.mil/portal/site/mari...i_baseMenuID=e106a3b5e50edce1fec24fd73927a759

maybe the above link, will be usefull for someone, which like to learn how to fix a position line or find the compass error !

to fix a position using the stars/sun you need to have an almanach, sight reduction tables, correct time and of course sextant! for more reliable position, it is better to plot 5-7 lines!
once you are used to it, this can take about 30 min from start to finish!
if used air navigation table or calculator, the time can be slightly reduced !
before to commence, need to prepare an info for stars to be used (star finder) - approximate azimut and altitude for each star !
it will be nice a man to have a little knowledge for latitude, declination, LHA, azumut, celestial horizont not compulsory but, how to correct the observed star's/ sun's altitude is an obligatory !

the theory can be difficult, as use a lot of trigonometry, but the use of tables only looks !

hope this help
regards


www.neatcss.com

Again, you see, what happens is that in the dumbing down process in which this era is unfortunately gripped, by attempting to make things easier what results is a fuddle, a total mess.

Calculatinjg an azimuth, which is a true bearing of a star or planet, in order to ascertain the compass error (which includes corrected variation and deviation) is not that complicated if proceeded along in the classic time honoured way.

The arguments are Latitude, Hour Angle and Declination.

You need to have accurate time and you need to have an accurate position to work from.

You need to have an accurate time (using a properly rated marine chronometer) to be able to properly calculate the Hour Angle and the Declination, which, specifically for this calculation are time dependent.

These values are extracted from The Nautical Almanack, which is the benchmark publication. Every other publication is a diluted version of this official publication, I regret to have to point out.

Then these results are worked (and interpolated as necessary) by using Burtons Tables (Royal Navy Preferred) or Nories Tables (Merchant Navy Preferred). Both results are identical in accuracy. I have both copies, but I prefer Nories because I was taught in Merchant Navy College to use these, and also, because the print is bolder and larger.

 

[snowleopard]

I will just reiterate a point I made earlier. The old Board of Trade Yachtmaster required NO sea time, nor did it require the candidate to demonstrate any boat handling skills or ability to command a crew.

The fact that the Astro section required a few skills that are no longer tested does not make the olds-stager a better seaman.

I will nail my colours to the mast:

A person who passed the BoT Yachtmaster with the MINIMUM skill set would not be fit to command a rowing boat on the Serpentine. A fast-track RYA yachtmaster with the minimum qualifying experience still has a lot to learn but should be capable of taking a crew to sea safely.

Before you flame me for this be sure to read the whole of this post.