Sextant.. Navigation tool or ornament?

[Lady Campanula]

Counting on my fingers, it appears I still have 3 sextants.... One Indian copy, one donated by a frustrated friend, and one given to me by HRH TPR.

The plastic Ebbco went to a keen forumeer, and the aircraft 'bubble' job went to a glass cabinet in the RIN.

I now have 4 GPS receivers.... one in the new/old boat, one GPSMAP76 given to me by a real sweetie at Garmin, one Trimble swopped-in for a 12V helo rescue winch pack, and a little Garmin GPS12.... I suppose that's progress of a sort.

But there's only one of me, and I'm redundant! And confused...!

 

[Seajet]

Lady C,

as I am sure you are aware, the 'Bubble Sextant' was invented by Francis Chichester ( had to sail and fly around the world to get a 'Sir' but fiddling politicians do it every day ) - to others I cannot recommend it too highly, for sheer adventure let alone amazement at navigational skills have a read of ' The Lonely Sea And The Sky '.-You'll have to buy an old copy as it doesn't seem to be in print, but I promise it will be worth the odd few pence.

I am just a mortal but I have still found a sextant helped me out, for coastal fixes.

 

[Blue5]

Well I learnt to use one just for the pleasure of doing it but I will freely admit that if I tried to use it in anger I would first have the instruction book out again.

I think If it is not a skill you have learnt and used frequently you would struggle to have confidence in your sights.

We maintain an hourly log when on passage so if the electrics went down we would have GPS position from last entry and I think I would probably trust my DR position rather than a dubious sextant sight.

 

[Seajet]

NDH,

I agree a log is essential; but a sextant - and for that matter a trailing log, and magnetic compass if we're talking 'old kit !' not to mention depth sounder / lead line can still give a distance off if one's batteries have failed for more than a few hours.

I also would need a quick read of the instructions ( though a lee shore is a pretty good wake-up call ! ) which is why I strongly believe in 'refresher courses' even - or especially- for people who've sailed for decades...

It depends on how much of a believer in Murphys' Law one is, personally I plan for the worst and hope for the best.

 

[Lady Campanula]

Lady C,

as I am sure you are aware, the 'Bubble Sextant' was invented by Francis Chichester ( had to sail and fly around the world to get a 'Sir' but fiddling politicians do it every day ) - to others I cannot recommend it too highly, for sheer adventure let alone amazement at navigational skills have a read of ' The Lonely Sea And The Sky '.-You'll have to buy an old copy as it doesn't seem to be in print, but I promise it will be worth the odd few pence.

I am just a mortal but I have still found a sextant helped me out, for coastal fixes.

Thanks, 'Seajet'. I've had a copy of SFC's book for years. Akshully, it's my second copy - the first was 'borrowed' with my complete collection of Moitessier's books.

Not many now know that he was a famous aviation pioneer before he took up single-handed ocean record chasing - at the age of 65, so I'm told!!!

He also wrote most of the RAF's 'AP3456G - Manual of Air Navigation'. The 'principles of air navigation' were borrowed from marine best practice, then adapted and modified to meet the different needs. 'Airmanship' and 'seamanship' have common roots.

He was something of a 'tearaway' in his flying exploits, and rumour has it that he was told at one final stand up interview in the Ministry - after some outrageous breach of the rules - that "You're too famous for us to take away your flying licence, but you WILL NOT pass your next flying medical...." So he turned to chasing ocean sailing records instead.

Quite what he'd make of our namby-pamby, 'PC' society today is anyone's guess.....

 

[snowleopard]

Lady C,

as I am sure you are aware, the 'Bubble Sextant' was invented by Francis Chichester ( had to sail and fly around the world to get a 'Sir' but fiddling politicians do it every day ) - to others I cannot recommend it too highly, for sheer adventure let alone amazement at navigational skills have a read of ' The Lonely Sea And The Sky '.-You'll have to buy an old copy as it doesn't seem to be in print, but I promise it will be worth the odd few pence.

Chichester was a famous user of the bubble sextant and famous for his 'find the island problem' when navigating to Lord Howe Island en route from NZ to Australia. He didn't invent it..

In 1919, sextant design advanced with the invention of a bubble artificial horizon by Lionel Burton Booth and William Sydney Smith, of the Royal aeronautical Establishment (Rae) at Farnborough.

 

[alant]

Of course you could just compare the readings of 2 separate GPSs. It's a bit like the blonde who knew she was having twins because she did 2 pregnancy tests and they both came out positive.

But isn't the information on both coming from the same source?

Bit like checking the fix from a red hand held compass, against the same fixes using a yellow one surely.

 

[timbartlett]

But isn't the information on both coming from the same source?

Bit like checking the fix from a red hand held compass, against the same fixes using a yellow one surely.

Or checking two lots of pee from the same pregnant blonde?

But it's an easier trap to fall into now than it ever was. Some cruise ship (Royal something??) ran aground on Nantucket shoal a few years ago because a wire came off her GPS antenna. She ended up (effectively) with two navigation systems both calculating DRs from the same data, coming up with the same answers and assuming that they were both correct!

The fact that the water was shallower than it should have been, and that there was a bleeding great lighthouse that shouldn't have been visible at all went unnoticed...

 

[Nostrodamus]

It is intresting that nearly all the replies come from those who have used a sextant.
Do you think those who have never used one are lost somewhere?

 

[scotty123]

Last time I used one in anger was on a cross-channel passage in hazy conditions. We had a total electrical failure and after about 70 miles without a fix we needed to find our way into St Malo avoiding the hard bits like the Minquiers and Roches Douvres. An afternoon sun position line gave us a clear lead in and we made a perfect landfall.

I don't normally take the sextant when coastal cruising but always have it on board with the necessary tables for long passages.

Can you pls explain how you were able to work out yor position from one position line.

 

[Lady Campanula]

Can you pls explain how you were able to work out yor position from one position line.

Almost certainly much the same way as the famous Captain Sumner, who managed a single sun sight in the Celtic Sea, under sail, after many days without any such Line Of Position to refine his Deduced Reckoning.

His skilled calculations indicated that, if he sailed straight up that LOP, he'd most likely 'raise' the Smalls Light off SW Wales. He posted some good lookouts, 'proceeded with caution', and eventually did raise the anticipated beacon more or less ahead. By estimated range and magnetic bearing - and, no doubt, a depth 'reduced to soundings' as another LOP - he then had a good 'fix', which allowed him to adjust his course in comparative safety towards Holyhead and Liverpool.

Some years later he published his successful procedure, and the 'Sumner Line' - adopted by most master mariners thereafter - eventually became the 'Marc St Hilaire Method' we have used since.

So, a single position line which passes through the landfall beacon for the St Malo approach channel and, of course, one's own position, permits one to sail down that LOP - allowing for tide set, leeway, and all the other little errors that man is heir to - and expect to see, before long, that elusive seamark.

Always provided there aren't any rocky sticky-up bits in the way, such as the Roches Douvres......

Navigation is a thinking skill - it is not done on a chart, but between the ears.

 

[scotty123]

Almost certainly much the same way as the famous Captain Sumner, who managed a single sun sight in the Celtic Sea, under sail, after many days without any such Line Of Position to refine his Deduced Reckoning.

His skilled calculations indicated that, if he sailed straight up that LOP, he'd most likely 'raise' the Smalls Light off SW Wales. He posted some good lookouts, 'proceeded with caution', and eventually did raise the anticipated beacon more or less ahead. By estimated range and magnetic bearing - and, no doubt, a depth 'reduced to soundings' as another LOP - he then had a good 'fix', which allowed him to adjust his course in comparative safety towards Holyhead and Liverpool.

Some years later he published his successful procedure, and the 'Sumner Line' - adopted by most master mariners thereafter - eventually became the 'Marc St Hilaire Method' we have used since.

So, a single position line which passes through the landfall beacon for the St Malo approach channel and, of course, one's own position, permits one to sail down that LOP - allowing for tide set, leeway, and all the other little errors that man is heir to - and expect to see, before long, that elusive seamark.

Always provided there aren't any rocky sticky-up bits in the way, such as the Roches Douvres......

Navigation is a thinking skill - it is not done on a chart, but between the ears.

Didn't he assume many latitudes & worked out that the position line went directly to the Smalls LH.

St Hilaire used the difference betwwen observed & calculated, from assumed position, so a bit different.

Maybe Snowleopard could give his version, cos " a single position line which passes through the landfall beacon for the St Malo approach channel and, of course, one's own position, permits one to sail down that LOP - " seems more luck than judgement, particularly on approach to St Malo.

 

[JayBee]

A common question in the astro-nav papers in MOT/BOT/MCA professional exams was to calculate the best time to obtain a position line from a sun observation, to assist a safe passage in deep water between two low lying Pacific atolls.

Step one was to determine the safe course and hence the direction of the desired position line and the azimuth. Step two was to work backwards from this using the DR Lat and Lon and get to the LMT via the GMT.

Astro navigation is a lot of fun and by no means redundant. With GPS all your eggs are in one basket, no matter how many backup receivers you may have on board.

I like sextants and own three nautical instruments and two of the bubble variety (for my next expedition to the Sahara), or just to check that my house is still where the GPS says it is.

 

[maxi77]

I take it some people haven't heard of failed generators ( whatever type ) and flat batteries, which includes a locker full of AA's and a handheld !

I agree most of us use things like GPS most of the time, and the user-friendliness makes it a distinct aid to safety especially if with a small - or no- crew at night.

Totally relying on it with no back-up is like applying in capital letters beforehand to be included in the ' There I was / Sod's law '/ next edition !

Equally have you never heard of clouds mist and fog, all of which can stop you taking astro sights. I have done several Biscay passages where no astro was possible and you had to depend on RDF and Consol until you got within Decca range Having a good departure fix, DR and EP is important, probably more so than having a sextant.

You need to plan for reasonable possibilities so I would not see a sextant as essential for some of the shorter out of sight of land passages, many of which were quite succesfully completed by yachties without sextants before the days of affordable radio aids. I have no problem at all for those who enjoy astro doing as much as they can, I don't and am quite happy using alternatives.

 

[Seajet]

I don't think anyone was suggesting a sextant - Not necessarily for astro - is proof against all weather, just that it is one of the many things a navigator should have in his locker, until we can all fund the launching and maintenance of our own satellites, and create on-board perputual motion generators.

 

[Lady Campanula]

Didn't he assume many latitudes & worked out that the position line went directly to the Smalls LH.

St Hilaire used the difference betwwen observed & calculated, from assumed position, so a bit different.

Maybe Snowleopard could give his version, cos " a single position line which passes through the landfall beacon for the St Malo approach channel and, of course, one's own position, permits one to sail down that LOP - " seems more luck than judgement, particularly on approach to St Malo.

AIR, Captain Sumner's procedure of resolving for several assumed latitudes was normal for his day. He 'observed' that the same Line of Position resulted and deduced that his position lay on - or close to - that line, which happened to run through the position of the Smalls Light. He wrote up and published his further-developed procedure some time later, and that developed a degree of acceptance. If one substitutes 'was developed into' for my 'became', that would better describe the later role of the 'Marc St Hilaire' assumed position/intercept technique on which most air astro became focussed.

Not many enthusiasts would now use the Haversine method of reduction, but one who does is Cdr Harry Baker in his 'Reed's Astro Navigation Tables' ( or, as he originally and mischievously called them, 'Reed's Heavenly Bodies' ). That's a very cost-effective and concise volume for the cruising yachtsman to carry.

Another enthusiast who resolved his sights the long way was Sir Francis Chichester. Picture him flying his open-cockpit biplane at 50 feet over the Tasman Sea, marine sextant on a cord around his neck, steering with the stick between his knees, his chart, dividers and pencils in his lap, and wrestling with the complexities of a tubular slide rule in both hands.....

Now that's doing it the hard way....!

 

[snowleopard]

Can you pls explain how you were able to work out yor position from one position line.

I didn't need to work out my position. Note that it was an afternoon sight so it ran NW-SE. I simply had to sail East or South until the transferred position line passed through the landfall point (an offshore buoy) then sail down the bearing of the position line. It's just a modification of 'running the Easting down'.

 

[Beadle]

I assume the astrolabe has been relegated to 3rd standby

 

[planteater]

GPS availability has always exceeded clear skies in my experience.

I do love old stuff and have great respect astral navigators with Seagull engines.

 

[VO5]

It is intresting that nearly all the replies come from those who have used a sextant.
Do you think those who have never used one are lost somewhere?

Not exactly lost but off course in their thinking perhaps...

I refuse to give up my hard earned skills.

I have a GPS on board, which I consider a great luxury.

But I have two sextants, a Carl Zeiss Yacht Sextant and a Heath Hezzanith, plus all the gear....Patek Philippe Chronometer, two stop watches, Nories, The Natical Almanac, Ship's Clock for LMT and Stiking Clock for the watches.

I also have an Azimuth Mirror, which I use as often as opprtunities permit,
to check the compass by taking Azimuths,

I know many will disagree, but in my book, there is nothing to beat a Mark 1 eyeball.