Celestial navigation practices


Mar 22, 2003
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Charts should have plenty of bearing lines defined by two visual points, that may be either landmarks or tangents.
After the Hawke collided with Olympic in the Solent back in 1911, Hawke's Lt. Aylen took a fix with reference to bearings that were taken off four specific landmarks. The magnetic bearing lines of the fix (shown in red below) were: S88W [252°T] to Egypt Point, S34W [198°T] to the east bank of the River Medina, S31E [133°T] tangent to the east shoreline of the Isle of Wight, and S10E [154°T] to the bathing house on Old Castle Point.That was not the point of collision but rather the point where Hawke came to a stop following the collision. The most likely point of collision would have been about 100 yards bearing about SE true from Aylen’s fix position.
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Doug Criner

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The bearing lines on charts that I am familiar with are true bearings. Many ships today (but of course, not in 1911) use a gyrocompass, but if a sailor is using a magnetic compass, then he needs to correct to true or vice versa.
 
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Mar 22, 2003
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Hi Doug, your absolutely correct.
The reported magnetic bearings such as S88W to Egypt Point were as given by Lt. Aylen in evidence. The true bearings, after correcting for magnetic variation (which was was almost 16°W in that region on that date) was therefore 255° True as indicated in brackets. This 16° correction, which was obtained from a channel pilot publication after correcting for annual change in variation, was applied to all four magnetic bearings given in evidence, and those lines were then drawn on the chart which resulted in the crossing point shown. It was great fun to do when Mark Chirnside and I wrote our book.
 
Mar 22, 2003
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By the way, anyone interested in that 1911 collision between Hawke and Olympic, you can pick up a copy here:
.
 

Scott Mills

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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.
Celestial navigation! Psh. They should have just used their GPS. ;)
 

Georges G.

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Hi Doug, your absolutely correct.
The reported magnetic bearings such as S88W to Egypt Point were as given by Lt. Aylen in evidence. The true bearings, after correcting for magnetic variation (which was was almost 16°W in that region on that date) was therefore 255° True as indicated in brackets. This 16° correction, which was obtained from a channel pilot publication after correcting for annual change in variation, was applied to all four magnetic bearings given in evidence, and those lines were then drawn on the chart which resulted in the crossing point shown. It was great fun to do when Mark Chirnside and I wrote our book.
Well as far as I know, a visual bearing taken from a magnetic compass gives a Compass Bearing, not a magnetic bearing. A compass bearing have to be corrected from the magnetic Deviation and the Corrected Variation to give a True Bearing.

You had to note the compass heading, the compass bearing and of course the time. Then you had to apply the variation to the compass heading to find out the magnetic heading. From the Magnetic Compass Deviation Card, you could then estimate the deviation. Once done, you could correct the compass bearing from the deviation to deduce the magnetic bearing and from there; you could apply the corrected variation to the magnetic bearing to finally deduce a sort of True Bearing.

At the end of the day, you would end up with a cocked hat that you had to investigate. If the land marks were spread over 360° you had a chance to be inside the cocked hat, but if they were only spread oven 180°, you were most probably outside the cocked hat. Another ball game …

compass bearing
+/- deviation
magnetic bearing
+/- variation
true bearing
 

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Georges G.

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A Gyro Compass bearing has its limit as well. The Latitude and Speed Corrector has to be properly set. Even though, the precision of the instrument is plus or minus 1°. Over one nautical running mile, you will land up 106 feet off track. That off track distance could ruin you day as a pilot. It is rare that a Gyro compass is perfect. I’ve seen some with over 10° error !!!
 

Scott Mills

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I imagine they still require celestial navigation for the merchant marine; however, it seems one of those borderline skills. Not yet entirely antiquated; however, with the proliferation of GPS and solar charging technology, and the fact that nothing barring a nuclear war or apocalypse level solar activity will make either the NAVSTAR or GLONASS satellites disappear, it seems very damn close to antiquated.
 

Georges G.

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The greatest threat to navigation is the Kraken!

I would say that most maritime colleges still teaching astronav, but … by iPhone. The only things you need to know is how to take a sextant sight and read the micro meter drum, how to enter a few fix corrections, where to clic on the software to enter automatically the UTC of observation and maybe, how to take a gyro bearing. With that information, the program will find out which star or planet it is and will calculate a most probable fix position in latitude and longitude in seconds.
 

Georges G.

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When I started studying Celestial Navigation, we had to do all the calculations strictly by hand using only paperback tables. Then we were allowed to use a calculator. After that, we could use the HO 229 rapid tables. In practice, we finally had the chance to use the Tamaya dedicated astronav computer. Along the line, I bought my own computer, a Cassens & Plath barrel sextant, an ebony & ivory Spencer Browning & Rust of London octant and a F. Barber & Sons pocket sextant.
 
Mar 22, 2003
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If you're going to use an iphone, you can get your position in lat and lon off the GPS within seconds without having to bother with taking sights. It takes all the fun out doing things. By the way, prior to HO 229, which became popular in the mid 1970s, there was HO 214. And then there is the old collector's item called HO 211, sometimes referred to as the ideal lifeboat nav table, just 49 pages in a pocket sized volume.
 

Georges G.

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If you're going to use an iphone, you can get your position in lat and lon off the GPS within seconds without having to bother with taking sights.
I must agree but still ... that would be roughly the millennium astronav technique if the extraterrestrials would swallow out the whole GPS & Glonass satellites constellation … :oops:
 

Jim Currie

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You lot had it easy. My first sextant was an Admiralty pattern vernier sextant with a little magnifying glass to read the silver vernier scale and three star tellescopes. The first thing taught to an Apprentice reggarding the use of a sextant, was the proper method of extracting it from its box. here it is
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Scott Mills

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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.
Sam,

Agreed! And it is not just NAVSTAR and GLONASS satellites anymore. China continues to build its Beidou satellite global positioning system, the European Union has Galileo (which will be fully deployed by the end of the year), and the Indian government is working to expand its IRNSS system.

So, in the next decade, you will have not one, not two, but at least 5 global positioning satellite systems with full coverage of the globe; and as you say, these things are here to stay--unless there is a nuclear war, or some apocalypse level solar activity.

And of course, you're right about GPS system breakdown. A modern smart phone has GPS built in, which works regardless of whether or not you have paid your bill! Combine that with the now ubiquitous portable solar chargers on the market, there is hardly any scenario I can imagine where someone could be stuck at sea and not have access to GPS coordinates--at least not a scenario where they could also take readings from a sextant, then do the calculations they would need.
 
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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.
You won't even have to do that. With the low orbit sat system they are putting up you'll be able to connect to the internet anywhere on the planet. Just hit your "where am I" tab on your phone.
 
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Jim Currie

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The way the world is going, there won't be any need to know where you are...you will be wherever your smart phone is and you don't need to move to use it.

However, what will you all do when Cyber warfare knocks out each country's smart bits of hardware in orbit? Or you all become vegetarians using fresh air for fuel ;)
 

Jim Currie

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I thought you would have used an electronic Astrolabe, Georges.:cool:
PS that really was a picture of the first sextant I bought for £12. Not the first one I had though. It came from the loft of the James Watt Nautical College. I found it when clearing out the l;oft of all bits and pieces. It really was old...had a little wooden handle an circular frames supports. Wish I had it now...it'd be worth a bob or two.
 

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