Celestial navigation practices

A. Gabriel

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You know now that I think of it, we haven't really had a dedicated thread for navigational art and practice in 1912, so I figured this would be a good place to start. But now is also the time for me to reveal the depths of my ignorance regarding such an arcane and interesting topic -- this is a subject on which I have only dared look into very recently so pardon if I come across as an absolute buffoon talking out of the wrong end of the GI tract.

So far from what I've read of the inquiry transcripts I can only find passing references to taking star sights for latitude and longitude from 4th Officer Boxhall's testimony. Many articles written by members more experienced than myself also mention the noon sight for latitude -- Dave Gittins in particular has an article somewhere here detailing the various navigational techniques expected of different levels of certification.

One question I have regarding the noon sight is whether the chronometer was used for the calculation of latitude? I know the method of latitude by noon sight involves the use of solar declination tabulated in the Nautical Almanac but I'm not sure if the chronometer was a must for this technique in those days.
 

Doug Criner

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The chronometer simplified calculation of longitude. If you know the GMT of local apparent noon (when the maximum altitude of the sun is measured with a sextant), then that will give you the longitude, even without a nautical almanac. Latitude in the northern hemisphere was measured by the altitude of Polaris, long before the advent of chronometers. Before the chronometer, mariners used an hour glass to "sort of" keep track of time, but that was very rough. Magellan's crew, upon sailing around the world, lost track of a whole day, and were totally mystified. (I say Magellan's "crew," because Magellan himself was killed by natives before returning.)

Columbus "discovered" North America before the advent of the chronometer - so he was perhaps uncertain of his longitude. That allowed him to believe (or claim) that he had reached China.
 
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A. Gabriel

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Magellan's crew, upon sailing around the world, lost track of a whole day, and were totally mystified. (I say Magellan's "crew," because Magellan himself was killed by natives before returning.)
Ironically Magellan’s voyage (whose quincentenary is already under way this year) is part of the reason I’m asking this question haha. Latitude by solar noon makes use of tables of solar declination throughout the year, but from what I could find the declinations are tabulated only for Greenwich apparent noon and mean noon (I’ve also seen American nautical almanacs with declinations tabulated for Washington apparent noon and mean noon).

I guess what I’m trying to get at here is did they use a given declination value for the day as-is in calculating for latitude, or did they have to extrapolate the tabled value to correct for the time difference between Greenwich and their location?

[Bonus side note, I’ve actually visited the place where Magellan was killed. It helps that I’m actually from the Philippines itself haha, the fact that we killed him is kind of a big deal in our history.]
 

Dave Gittins

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Actually, the better you know UTC, the more accurately you can get latitude. Tables give the declination of the sun as it changes throughout the year. In April declination is increasing at about 22' every 24 hours. When you look up the tables, you can interpolate the exact declination for the time of your sunsight if you know UTC. Every 1' error in the declination is a mile error in latitude. On Titanic the UTC could be checked from the chronometer but earlier navigators used a bit of rough judgement. In any case, their instruments were not much use. Magellan would have used an astrolabe, which gave quite crude results. I've seen observations by Francis Drake that are a good degree out.

By the way, you can't get an accurate longitude from the noon sight. The sun seems to hang in the sky for some time and you can't get the exact time of its maximum altitude. Lazy yachtsmen have been know to try this, but it would never do on a properly run liner.

All sorts of rough methods have been used. The yachtsman Vito Dumas, in the Southern Ocean, got longitude by comparing his time of sunset at his guesstimated position with the time of sunset at Greenwich. He was only trying to find South America, so he managed quite well.

Hooray for GPS!
 

A. Gabriel

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From the sound of it, the chronometer was used for fine accuracy in the latitude calculation. I'm assuming the longitude for the noon position was obtained by dead reckoning from a previous fix then?

Thank goodness for GPS indeed, but here's hoping the old arts will still survive to be passed down to succeeding generations of seafarers.
 

Dave Gittins

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You have it right. The procedure on a major liner was to get a fix just before dawn, using multiple star sights to get latitude and longitude. This could be carried forward by dead reckoning to give a pretty good noon longitude. Alternatively, a sight for longitude alone could be taken at around 9-00am and carried forward. In 1912 they were keen on sights that gave longitude alone, without chart plotting. Only Extra Masters were required to know Sumner position lines and the short tables, like HO249 were still to come.
 

Dave Gittins

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I use GPS most of the time. I even use it when returning from a short sail when I have to find a certain beacon against a land background. The great thing to remember is that the charts are less accurate than the GPS. Every chart has a Zone of Confidence diagram which shows how big the errors in the chart may be. It's common to be in Zone C, where errors of up to 500 metres will be found, so don't kid yourself you are going to miss that big rock by 200 metres. It may not be where the chart says it is!
 

A. Gabriel

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So far I’m trying to get a handle on what the reference materials for navigators would have been in those days (and perhaps now, if they’ve survived into print this far). The most principal one I’ve found so far is of course The Nautical Almanac and Astronomical Ephemeris for the Year xxxx for all the tabulated data on times and positions of celestial bodies, and then there is Norie’s Nautical Tables which I am pleased to note is still in print.

Incidentally I had a look at the inside of the American Ephemeris and Nautical Almanac for 1912 (an online copy of its British counterpart titled as above could not be found), and found the interesting little tidbit that in the column for the moon’s transit of the Greenwich meridian, the entry for April 17 only contains the symbol for “conjunction”. Apparently there was a solar eclipse visible from London on that date?
 

Dave Gittins

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There was a solar eclipse on 17 April. It was mostly annular. See Wikipedia.

I only know what the British did. To brush up on navigation they had Nicholls's Guide to the Board of Trade examinations. This was published under various names well into the 20th century. A very popular book was Wrinkles in Practical Navigation, by Captain S T S Lecky. This ran to many editions and was big enough to serve as ballast. I have 1918 edition that I found online somewhere. Americans had books by Bowditch, but I don't know the details.

A look at the worked examples in Nicholls will give you respect for the navigators of 1912.
 
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1918 edition of Bowditch had a 20 page chapter describing the practice of navigation at sea, beginning with morning sights and ending with the 8pm position, including examples of course. The 1918 edition is available on-line somewhere in pdf format. I have downloaded it as a reference. Here is just a smidge taken from that:

1575416317861.png
 

Doug Criner

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Didn't they include dawn and evening star sights? That's when the horizon is most clear and star altitudes can be measured most accurately. As I recall while serving on a small naval ship, the navigator stood no watches - he was up at all hours for star and sun sights, as well reducing sightings for a fix, and taking and plotting bearings when near land. He had one primary assistant, a senior quartermaster. (In the army, a quartermaster stores and issues equipment and supplies, but in the navy, quartermasters help navigate.)
 

Jim Currie

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There was a solar eclipse on 17 April. It was mostly annular. See Wikipedia.

I only know what the British did. To brush up on navigation they had Nicholls's Guide to the Board of Trade examinations. This was published under various names well into the 20th century. A very popular book was Wrinkles in Practical Navigation, by Captain S T S Lecky. This ran to many editions and was big enough to serve as ballast. I have 1918 edition that I found online somewhere. Americans had books by Bowditch, but I don't know the details.

A look at the worked examples in Nicholls will give you respect for the navigators of 1912.
Hello Dave.

As you know, Nicholl published 2 volumes. Volume 1 was used to instruct Apprentices and Candidates to the level of 2M(FG).
Volume 2 was very advanced and was used from 1M(FG) up to and including Extra Master. I still use my Nicholls's V2 but I always used Burtons Tables instead of the more popular Nories Tables. Simply because the former had 5 figure logarithms and to me, were more accurate. For authenticity when checking the evidence, Is still use y 1950 copy, but they are, like me, becoming a wee bit sad.

In 1950, they used exactly the same navigation methods as were used in 1912. In fact, my Navigation Instructor was 2nd Officer at sea in that year, I's sure you remember the attached.

By the way, As a dedicated Navigator for 4 years... 2 of which on passenger vessels... I can tell you that the Traverse Table was never used except as a check to the results of a calculation done the "long way".
 

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A. Gabriel

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Didn't they include dawn and evening star sights? That's when the horizon is most clear and star altitudes can be measured most accurately. As I recall while serving on a small naval ship, the navigator stood no watches - he was up at all hours for star and sun sights, as well reducing sightings for a fix, and taking and plotting bearings when near land. He had one primary assistant, a senior quartermaster. (In the army, a quartermaster stores and issues equipment and supplies, but in the navy, quartermasters help navigate.)
Sam's Bowditch excerpt seems to be referring to early morning and late afternoon sun sights, when the sun is high enough in the sky to escape the bothersome effect of refraction, which would otherwise need to be corrected for in the case of a low-altitude sight. On a related note, one wonders how large the height-of-eye correction for the sextant reading was on Titanic -- taking sights from the boat deck, so high above sea level, would presumably give rise to an uncommonly large "dip".

In any case Boxhall definitely testified to the use of star sights as SOP during the American inquiry (was that the intercept / Marc St-Hilaire method?). Maybe Bowditch discusses it on a different page, it is a fairly large chapter by the sound of it.
 

Dave Gittins

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Boxhall was talking about the methods that gave latitude and longitude purely by calculation, with no plotting on a plotting chart. You observed stars lying roughly east or west for longitude and stars lying north or south for latitude. The Mark St-Hillaire method was only required for Extra Masters and old hands regarded it with suspicion, because of the plotting and possible errors. The old methods made a comeback in the 1980s, using programmable calculators that also contained data about the celestial bodies. I assume the work can now be done on a computer.
 

Jim Currie

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Hello Dave.

You might also add that a calculated Latitude and a calculated Longitude are both position lines upon which the vessel is located at a specific point on the line.

They would have used position lines way back then, and would have used either squared paper or an Aqino's Protractor much like the the one shown here if they wished to do a plot.
Aquino 2019-12-07 001.jpg


These were being taught for Mate and Master s late as the 1960s. Although by then, the Marc St Hilair method was the method of preference.
 
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If your GPS breaks down then what!
Sorry Mike, but the 21st century is here to stay. These days you can use even use a cellphone to get your lat/lon coordinates from the GPS satellites, and then you just have to plot it on a chart. There are some more expensive marine GPS units that also could use the GLONASS system as a backup, which is the Russian version of GPS, in the remote case of the US maintained GPS system failure.
 
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