# Sight reduction tables



## Julian Calvin (Feb 2, 2011)

As one who loved taking 'stars,' when were the above first introduced. Know they made life easier but cannot remember by how much.
Always tried to precalculate as much as possible plus do my best to find one on the meridian. Surprising how often this was possible.

Still have my book of calculations but only numbers listed and cannot now remember the specific tables used in my Nories. Suppose I should just look up the most dog eared pages.


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## borderreiver (Oct 11, 2008)

always enjoyed sights. one of my buckets tasks was to get a star position on to the chart before sunset. very close but never achieved.


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## greektoon (Oct 17, 2008)

I remember using sight reduction tables for air navigators on all my pre-sat nav ships. I would shoot about 8 stars at a time - very satisfying. I also still have my old sight books.


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## Nova Scotian (Jul 2, 2006)

*Sight Reduction Tables*

I first became aware of sight reduction tables for stars in the late sixties. I think they were called HO 229's or something like that. I can remember buying a set of three volumes of sight reduction tables and plotting sheets prior to joining the Alva Star in 1971. 

Viewed with a great deal of suspicion by the old man who preferred long by chron'!


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## Stephen J. Card (Nov 5, 2006)

Long by Chron for the sun and Marc St. Hilarious for the rest!

By the time I was doing 4 - 8 I was I the modern era. Worked times of civil and nautical twilights and enter the book for LHA Aries and LAT, N or S. That have the seven stars. When finished with the sights I did the calculation by my trusty NC77. That was the same as doing 'traditional' calculation in Marc St. The Sight Reduction Tables were only for finding the stars. It was easier than the 'Star Finder'. I kept my own Reduction Tables, still have them. Took my own to sea on 'others flags', did not take the chance there was not a set on board! My tables were A.P. 3270 HMSO. The sextant is still good but the NC77 died. :-( 

There is a site on the WWW. All of these calculations can be done there IF your GPS packs in!

The Tables came out in 1950. Originally done by the US Hydro Office and came out 1947. By 1950 the UK, Canada etc came on board and it became joint effort.


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## Enri (Jun 24, 2008)

I heard that the tables were written by the Americans during the depression as a way to keep people employed. I had and still have a set in my "office", which I liberated at some time during my career, but If I recall rightly there was a correction to apply for the Epoch, which in the books I have, the last correction was for the turn of the century. Used to like taking stars, but like most things progress made the art obsolete. The little boxes giving the position down to metres took the fun out of the job. Still more time to do the mounting paperwork I suppose.


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## John Cassels (Sep 29, 2005)

Every ship in Denholms had copies on board. As far as I can remember , the word reduction was because all workings were reduced to your nearest latitude .


Or maybe I've been ashore too long.


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## greektoon (Oct 17, 2008)

I think there was a bit more to it than finding the stars but it's been a long time. I will dig out my sight book one of these days and check.


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## Stephen J. Card (Nov 5, 2006)

John Cassels said:


> Every ship in Denholms had copies on board.
> .



You will remember every Denholm ship had an extensive library. Not just nav books, but good technical books. Always something to read on the bridge!

I saw one book being thrown overboard! On 8-12 I was reading a 'home made' manual written by DG Ridley, 'Know your own OBO'. All you needed to know about AVON BRIDGE. Quite good, piping diagrams, hatch information, ballasting systems, Inert Gas etc. Quite hefty and all typed up. Useful for sure. One morning the OM came up, Peter Shawyer. He saw what I was reading and he started a bit of a rant. Peter hade been Mate in the AVON and he knew the ship completely. He did not take to Ridley and did not a like of the information in the book. After ten minutes of the rant Peter said, "Know your EFFIN' OBO! ********!" Grabbed the book out my hand, walked out to the bridge wing and threw the book overboard! I wish I had been able to keep it... even it wasn't the best book! Ah well.


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## 8575 (Sep 8, 2006)

I remember Ben Line ships in the 60s all carried the American 'Star Finder' perspex sheets, very robust compare to the British ones. Bank Line ships carried all the Reduction Tables for Air Navigation, very handy bits of kit when doing stars in particular.

When I was a cadet I remember a Ben Line 2nd Mate showing me how to make a homemade plotting sheet on the back of an old chart. Personally I preferred to dig out any large scale chart from the folios that coincided with the latitude we were in, whether it had land on it or not, just add your longitude values instead of the printed ones and that was it. Got funny looks at first but folk saw the sense of it; cheaper than buying plotting charts too.


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## vasco (Dec 27, 2007)

Waighty said:


> I remember Ben Line ships in the 60s all carried the American 'Star Finder' perspex sheets, very robust compare to the British ones. Bank Line ships carried all the Reduction Tables for Air Navigation, very handy bits of kit when doing stars in particular.
> 
> When I was a cadet I remember a Ben Line 2nd Mate showing me how to make a homemade plotting sheet on the back of an old chart. Personally I preferred to dig out any large scale chart from the folios that coincided with the latitude we were in, whether it had land on it or not, just add your longitude values instead of the printed ones and that was it. Got funny looks at first but folk saw the sense of it; cheaper than buying plotting charts too.


I did that from Walvis Bay to Santos. As luck would have it it was a cancelled chart of Walvis coast. Came on watch at midnight to find the Old Man had told the Mate to check the soundings crossing a 50m bank. Despite the fact we were 3 days out the om had thought we were only 50 miles off the coast.


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## lakercapt (Jul 19, 2005)

Enri said:


> I heard that the tables were written by the Americans during the depression as a way to keep people employed. I had and still have a set in my "office", which I liberated at some time during my career, but If I recall rightly there was a correction to apply for the Epoch, which in the books I have, the last correction was for the turn of the century. Used to like taking stars, but like most things progress made the art obsolete. The little boxes giving the position down to metres took the fun out of the job. Still more time to do the mounting paperwork I suppose.


So that's where they went Gary!!!!!!
Sight reduction tables and Rudds star identifier were great for the olden days and they seem archaic now with GPS.
Would not like to drive my car without it now as it tells me lane positioning and traffic collision etc. Wonderful little invented box too late for my sea going days!!!


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## Stephen J. Card (Nov 5, 2006)

One idiot master wanted the courses for a voyage of Florida to the English Channel. Used the huge plotting charts. Great Circle and all of the sights, sun and stars position plots were kept. He knew it was transatlantic and there was no land so it was safe. About four days later he ran aground off the north reefs of Bermuda. Harbour Radio tried to contact, even sent a helicopter out to contact him. He took the ground and thankfully missed the big reefs. 200,000 tonnes of Bunker C. Thankfully the ship was refloated without and spill. Sept 1984. Extra. The refloating took 9 day and following discharge t Rtdm the vessel was scrapped has damage was too extensive. The Chief Officer was playing with the Sat Nav at the time, in broad daylight. They had only one chart showing North AND South Atlantic. Hence use of plotting charts.


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## 5036 (Jan 23, 2006)

A pal of mine worked for P&O and when he took tne noon sight on the bridge wings he would have a sly *** as he was not allowed to smoke on watch. As he did one day, out of the corner of his eye he saw the old man coming through the wheelhouse door. He instinctively responded to ditch the cigarette over the side. The next thing he remembers is looking at the OM with a cigarette in one hand, no sextant in the other and a very sheepish grin. For his troubles he got a dressing down and had to purchase a new sextant.


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## Enri (Jun 24, 2008)

Sorry Bill, the reduction tables I liberated were from a laid up ship which was going foreign flag. Makes me laugh, if the sat Nav went down it was an excuse not to sail on the ferries, that or if we lost a radar, great when on a clear day you could see where you were going. My last world wide ship we were still required to take sights but unless they were vastly different from the black box nobody took any notice of them except to find the mistake in the calculations.


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## Stephen J. Card (Nov 5, 2006)

nav said:


> A pal of mine worked for P&O and when he took tne noon sight on the bridge wings he would have a sly *** as he was not allowed to smoke on watch. QUOTE]
> 
> 
> Why no smoking on the bridge? Safer to smoke inside than outside. You might throw a cig over the side.. worse... might throw the sextant overboard!


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## George Porteous (Jul 19, 2015)

Always enjoyed the satisfaction of my star sights on the 4 to 8. How small was your "cocked hat"?


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## Farmer John (Feb 22, 2012)

George Porteous said:


> How small was your "cocked hat"?


It is (was) wonderful how a very dated and archaic phrase survived as long as it has. WE nearly all know what it is, but probably only one in a thousand of us has ever worn one.


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## borderreiver (Oct 11, 2008)

George Porteous said:


> Always enjoyed the satisfaction of my star sights on the 4 to 8. How small was your "cocked hat"?


I plotted on a summers chart and also adjusted PL to a set time. most times the cocked hat was small.


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## slick (Mar 31, 2006)

All,
Was it "Dead Reckoning or Ded. Reckoning"?

Yours aye,

slick


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## 8575 (Sep 8, 2006)

vasco said:


> I did that from Walvis Bay to Santos. As luck would have it it was a cancelled chart of Walvis coast. Came on watch at midnight to find the Old Man had told the Mate to check the soundings crossing a 50m bank. Despite the fact we were 3 days out the om had thought we were only 50 miles off the coast.


At least you realised as I did that you could use suitable scaled charts to do the plotting. I always pinned a note in big capitals to say it was not the chart we were currently using, only for plotting.

A Mate I sailed with maintained that the smaller the scale used the better the 'cocked hat' would be!


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## John Cassels (Sep 29, 2005)

Waighty said:


> At least you realised as I did that you could use suitable scaled charts to do the plotting. I always pinned a note in big capitals to say it was not the chart we were currently using, only for plotting.
> 
> A Mate I sailed with maintained that the smaller the scale used the better the 'cocked hat' would be!



He had a point there , cos that would be the size of the CH.


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## madbob (Dec 30, 2006)

Sight Reduction Tables turned a long and boring star sight calculation into a pleasure. Every 4 to 8 watchkeepers friend long before the push button GPS style of navigation. Actually gave a quick and positive fix for the run up to Noon sights.
God bless America !


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## methc (May 4, 2005)

DR positions."Dead" or "D'eD" reckoning is properly Decided Reckoning. Reckoning being the old word for mathmatics. Remember the books call Ready Reckoners? A long time ago,at the end of each watch a peg would be put into a chosen hole in a special board indicating the course and distance sailed from the position of the previous peg. after 24 hours a string from the first to the last peg would indicate the average course and distance sailed. The position was a reckoned one.In time as navigation improved the Captain would make a correction for set and drift and when paper charts became the norm the reckoned position would be indicated in pencil as D'ed Reckoned and eventually this was shortened to DR.


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