# Bearing Corrector



## Ron Stringer (Mar 15, 2005)

One for the detectives amongst the radio clan aboard SN.

Can anyone shed any light on the item held in a Sydney Museum described as a 'Bearing Corrector'? 

Details on http://www.powerhousemuseum.com/collection/database/?irn=374864&search=commander&site_id=3

It well precedes the BT Direction Finders with which I was conversant but since it was a MIMCC product, there must have been a radio connection.

Who was Commander T J Hutchinson?

Any ideas?


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## Cisco (Jan 29, 2007)

Reading the description it sounds as if whoever wrote them was a bit confused as well...true magnetic bearing?

Not being able to see it I would hazard a guess that it converted a D/F bearing, which is a great circle bearing, into a rhumb line bearing ( for want of a better expression) that could be plotted directly onto a mercator chart. There is/was a handy little table in Nories that did the same job.... half convergency tables I think they are called... they can also be used to establish very simply the initial great circle course to steer.


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## surfaceblow (Jan 16, 2008)

There is only two Commander Hutchinson that I know of. According to my son he is a character in Star Trek. The other one was in command of the 16K Class Destroyer HMS Achates during the Battle of Jutland / Skagereavk 31 May - 1 June 1916.


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## trotterdotpom (Apr 29, 2005)

Couldn't it just be a device for working out the True Bearing after obtaining a Relative Bearing by DF. Did they have gyro repeater motors and what not in 1900?

I wouldn't have thought the range and accuracy of DF bearings would be good enough to worry about the difference between Great Circles and Rhumb Lines.

John T.


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## sparkie2182 (May 12, 2007)

As Cisco points out, the description is hardly the best.
The "Concentric Circles" may be for Half Convergency calculations, i cant think why they would be needed in a simple Relative to True calc.


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## Cisco (Jan 29, 2007)

trotterdotpom said:


> Couldn't it just be a device for working out the True Bearing after obtaining a Relative Bearing by DF. Did they have gyro repeater motors and what not in 1900?
> 
> I wouldn't have thought the range and accuracy of DF bearings would be good enough to worry about the difference between Great Circles and Rhumb Lines.
> 
> John T.


To convert back then ( and much later.... I recall seeing a post WW2 Hall Bros tanker with peloruses ( pelorusi? ) on the bridge wings)** from relative bearing to a compass bearing was a simple matter of singing out to the mate on watch or the helmsman depending on who was doing what.

You have forced me to disturb the cook and fossick around in the saloon bookshelves to find the ship's Nories.... this is a 1983 edition. 

Page 494. Name of table.... 'Correction required to Convert a Radio Great Circle Bearing to Mercatorial Bearing'.. I'm pretty sure that in my 1950/60ish edition at home they are called 'half convergency tables'.

Mean latitudes are given from 3* to 84*
Difference of Longitude of Ship and Radio Station is given from 2* to 30*

Sample correction... Mean Lat 57 degrees... Diff long 12 degrees ( in this latitude that is a distance of 359.5 miles according to the Traverse tables...)... correction to bearing is 5 degrees

Correction to always be applied towards the equator... ie if radio bearing in above example is 74 degrees then compass bearing is 79 degrees..

** the cook is always telling me I shouldn't talk in parenthesis... whatever that is.....


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## dfa1963 (Jul 4, 2008)

Page 77 of this link has reference to a Bearing Corrector as part of an article on "the Radio Lighthousse"


http://books.google.co.uk/books?id=...onepage&q=marconi "Bearing corrector"&f=false


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## sparkie2182 (May 12, 2007)

Convergency is d.long x sin of MEAN LAT and the respective
conversion angle is half of convergency, for rhumb Line 1/2 x d.long x sin mean lat and would be simplified by using the "Concentric Circles" to give a direct reading of
the correction to be applied...........i doubt a mechanical device to calculate Rel to True 
would have been thought neccesary.

I would not have liked to have been the one to have presented it to a "Three Ringer" Fleet Navigating Officer of the Royal Navy.


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## trotterdotpom (Apr 29, 2005)

I know what you mean Cisco, but Marconi weren't averse to coming up with some fairly "Heath Robinson" devices to perform odd functions - especially if they thought some dummie would buy them.

It's quite possible that the "objet" in the museum is a means of applying a correction for half convergency error, but as you say, there are tables for that.

The long range accuracy of Direction Finders, where "night effect" could also come into play, was crap, especially with a rusty old rotating loop. No doubt in 1900 they were regarded as a "modern wonder", but, in latter years, I'm sure you too used it to try and get some music on the bridge.

When the DF's were made capable of being activated by the radio room Auto Alarm, they were meant to be left tuned to 500 khz so that a bearing would be automatically taken of a ship sending a distress signal. Try telling that to a 3rd Mate with an Afro haircut and tye died tee shirt! Didn't take long before everyone gave up bothering about that little frill.

I'm going to Sydney in a couple of months, if nobody has come up with anything in the meantime, I'll go to the Powerhouse and have a look at the monster - maybe the instructions will be visible.

John T.


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## Cisco (Jan 29, 2007)

dfa1963 said:


> Page 77 of this link has reference to a Bearing Corrector as part of an article on "the Radio Lighthousse"
> 
> 
> http://books.google.co.uk/books?id=...onepage&q=marconi "Bearing corrector"&f=false


Brilliant link but I don't think it is the same thing.....
Reading the article I'm not surprised the watchkeeper has decided to go astern.....


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## sparkie2182 (May 12, 2007)

I often used to endorse D.F. bearings in the log with "Bearings possibly affected by night effect".

It never seemed to go down well.


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## trotterdotpom (Apr 29, 2005)

"The Radio Lighthouse" - "Marconi-Heath Robinson", I rest my case!

When I worked on the Nab Tower Lighthouse in Spithead, we had a DF transmitter which was switched on a couple of times a day and also during fog. There were no windows in the tower so we had to go out and have look at the visibility every now and then. One night I went out through the thick steel doors on to the "balcony" and couldn't see the handrail in the dense fog! I could hear what seemed like dozens of ships' whistles though.

I started the fog signal up (took a few minutes) and then the DF transmitter. The ships seemed to disappear almost at once and I thought: "It must make a difference," now I just wonder if they were still there but I couldn't hear them over our own deafening fog horn.

In 1999, the Nab was struck by "Dole America", a freezer ship - they must have forgotten about the "convergency correction"! Wouldn't have happened if there were still keepers there, harrumph!

John T.


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## Cisco (Jan 29, 2007)

looking at the bit of kit in Popular Science again.... is that an early form of Consol?


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## NJMC (Jan 15, 2014)

Ron, I found your old post on this "bearing corrector"! I recently purchased one and have been researching it, and have found very little.
Did you ever locate any info?

Photos in my original post. Thanks in advance, Mike
http://www.shipsnostalgia.com/showthread.php?t=55593


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## Ron Stringer (Mar 15, 2005)

Sorry, what you see on this thread is the sum total of the information received.


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