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Brains trust, who can answer this naval gun question?

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The gun in the last photo is mid-late 19th century, corresponding to a period when an expansionist Russia was perceived as a considerable threat to British interests in Australasia. Prior to that, it was the French who were being defended against.

 

Fort Denison, on Pinchgut island in the middle of Sydney Harbour was built after two American warships entered the harbour unobserved in 1839 and circled the island, less than a mile from Sydney itself, throwing a scare into the government of the time. Construction lapsed and the fort was only completed during the Crimean war.

 

Steven  

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Survey marks would normally not be vertical arrows. Indicators of magnetic North are temporary, magnetic North moves constantly and mass will pull a needle, so I doubt that is what they represent. Suspect it is a reference mark related to the pivot point of the gun, and used in orientating a indicator ring around the pivot point of each gun. Probably originally marked from astronomic observations taken from the pivot point of each gun, the numbers were probably file index numbers, close positions could use the same data but would need adjusting as distance increased between gun positions. Using rings indexed to the marks, fire could be concentrated to one close point by adjusting the paralex when using the marked rings, ' adjustments required from the dispersal points of the guns', when laying the gun using the preset rings, one gun was probably fired to obtain direction and range, all guns in the battery could then be brought onto the target using the indexing rings that had been orientated to the index marks. Sounds like a bunch of BS to me, but having been a Gunner and a Land Surveyor in my working years, is my non-researched best guess.

84392787_DIRECTFROMCEARCLICK054.2.jpg.132a7cd90856f72da158399dc556429e.jpg

 

Edited by jud

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Do Google maps show shallow water reefs etc. Guns are only useful if you know where you are shooting them. Its not like the Wild West of America where you have a AKA with a double clip to shoot a rabbit, Every shot counted as it took TIME to reload, Shots had to be made to count 

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On 8/31/2018 at 11:05 AM, Hubac's Historian said:

Perhaps a measurement above sea level?

You win the cookie!

 

A retired artillery officer went and had a look for me and this is his response (I didn't think there were decimal points but my son who has younger eyes than me assured me they were there and in the attached pic you can see why)

 

"I inspected the markings today at outer middle head.
The markings varied from 106 to 108.
There was no decimal point.  
The arrow is below  a centre line which reminded me of a survey mark.
Checking an ordnance map of the area it appears these markings are the
height above sea level of the gun's trunnion in each of the pit.
A couple of pits are at the same level and the others are slightly higher

which explains the variation in numbers.
Gun Height was, and still is, an important factor in calculating the gun's
trajectory."

 

108.jpg.eff22c72339d1adbfea1fa5ecf6f4f3c.jpg

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As a retired Chief Fire Controlman, I couldn't help but note the similarity between the carved horizontal line with arrow below and the rangefinder on the FC rating badge (see image below).  Anybody know when stereoscopic rangefinders came into use (and possibly the associated symbol)? 

 

 

 

image.png.39eb8381525681750d669d4fc28b60a4.png

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5 hours ago, el cid said:

As a retired Chief Fire Controlman, I couldn't help but note the similarity between the carved horizontal line with arrow below and the rangefinder on the FC rating badge (see image below).  Anybody know when stereoscopic rangefinders came into use (and possibly the associated symbol)? 

 According to this, around 1880.   There's more links but similar dates:  https://www.getrifle.com/history-legality-rangefinders/

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Don't think those numbers and arrows are intended to be used as Bench Marks. 10.6 is a very in-precise measurement, a tenth of a foot is approximately 1.2 inches if Imperial, reduced to decimal units, then there is the decision where to round off that last digit, several different rules and standards were and are used today. Elevations are typically given as hundredths and sometime thousands of a foot depending on the intended use, obtaining such precision is and was not that difficult, which in my mind, makes those numbers doubtful that they represent any Surveying standards for marking Bench Marks. A tenth of a foot would represent a lower standard of measurement than was needed to construct the Battery position and its buildings in the first place. It was noted above that the physical vertical positions would be closer to 10.6 meters above Sea level, rather than 10.6 feet, a tenth of a meter would be 100 MM, converted to feet, 3.94 inches or .328 feet. Suspect the experienced Artillery Gentleman had limited experience with fixed gun positions such as a coastal battery and was making a guess, perhaps tainted by the way the question was asked. So, the numbers not matching the physical elevation and the way the numbers were written, makes me question there use as Bench Marks, I will continue to wonder what they are, what they are intended to represent and how they were used. Hope someone has something in a reference library or knows offhand that would reveal what they are.

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On 9/9/2018 at 8:59 AM, jud said:

Don't think those numbers and arrows are intended to be used as Bench Marks. 10.6 is a very in-precise measurement, a tenth of a foot is approximately 1.2 inches if Imperial, reduced to decimal units, then there is the decision where to round off that last digit, several different rules and standards were and are used today. Elevations are typically given as hundredths and sometime thousands of a foot depending on the intended use, obtaining such precision is and was not that difficult, which in my mind, makes those numbers doubtful that they represent any Surveying standards for marking Bench Marks. A tenth of a foot would represent a lower standard of measurement than was needed to construct the Battery position and its buildings in the first place. It was noted above that the physical vertical positions would be closer to 10.6 meters above Sea level, rather than 10.6 feet, a tenth of a meter would be 100 MM, converted to feet, 3.94 inches or .328 feet. Suspect the experienced Artillery Gentleman had limited experience with fixed gun positions such as a coastal battery and was making a guess, perhaps tainted by the way the question was asked. So, the numbers not matching the physical elevation and the way the numbers were written, makes me question there use as Bench Marks, I will continue to wonder what they are, what they are intended to represent and how they were used. Hope someone has something in a reference library or knows offhand that would reveal what they are.

No you're thinking far too modern.

As the guy said, he checked the ordnance maps and confirmed the height in feet. No-one in the 1870's used decimal measurements and his inspection confirmed what I initially thought that there were no decimal points, it was just a trick of erosion. I can easily agree that they are at approx 106 feet above sea level, they are far more than 10.6mtr above sea level. I'm happy with his answer.

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I suspect the even-foot level of accuracy for the trunnion ring height was sufficient for ballistic calculations during the period, given the likely degree of precision in determining the other parameters (target range, speed or angular motion, target height, wind speed and direction, etc).  Lots of other variables come into play (powder characteristics, powder temperature, projectile characteristics, bore condition, rounds fired, barometric pressure, etc. etc).  All of these factors are precisely measured today but likely not considered or accurately measured prior to WW I.

 

Cheers,

 

Keith

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11 hours ago, el cid said:

I suspect the even-foot level of accuracy for the trunnion ring height was sufficient for ballistic calculations during the period, given the likely degree of precision in determining the other parameters (target range, speed or angular motion, target height, wind speed and direction, etc).  Lots of other variables come into play (powder characteristics, powder temperature, projectile characteristics, bore condition, rounds fired, barometric pressure, etc. etc).  All of these factors are precisely measured today but likely not considered or accurately measured prior to WW I.

 

Cheers,

 

Keith

Agreed, the range involved was minimal as the guns were for use once ships had entered the harbour so the range would be in the order of 1000 to 1500mtr tops I'd say.

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