Brains trust, who can answer this naval gun question?

[Bedford]

I took my son to Middle Head in Sydney Harbour on Saturday to see all the old gun emplacements dating from the 1790's through to the end of WW2 

On the old original emplacements (carved out of solid sandstone by convicts) was a bewildering sign. As indicated in the pic, there was the number 10.6 with an upward pointing arrow below the number carved into the side of the emplacement on three and 10.7 with an arrow on the fourth while another over the other side had 10.8 with an arrow.

 

Can anyone explain what it means?

 

Edited August 29, 2018 by Bedford

[mgdawson]

Hi Bedford

 

Some years ago i went to Bare Island Fort in Port Botany and a guide commented on some markings on the gun emplacement walls, possibly similar. Unfortunately I don’t remember details.

 

I think the Harbour Trust manages Middle Head, perhaps shoot them an email.

 

Oh, and don’t forget to let us know what they say 🙂

 

Mark

Edited August 30, 2018 by mgdawson

[druxey]

The 'broad arrow' mark was the stamp on things that were Government property.

[twintrow]

10.6 and 10.7 Degrees off N ?   That many degrees swing?   Would seem someone in the Fort would know.  The Docents are usually well informed on all things fort.

 

Tom

[Hubac's Historian]

Perhaps a measurement above sea level?

Edited August 31, 2018 by Hubac's Historian

[Bedford]

 

15 hours ago, mgdawson said:

Hi Bedford

 

Some years ago i went to Bare Island Fort in Port Botany and a guide commented on some markings on the gun emplacement walls, possibly similar. Unfortunately I don’t remember details.

 

I think the Harbour Trust manages Middle Head, perhaps shoot them an email.

 

Oh, and don’t forget to let us know what they say 🙂

 

Mark

Yes I think I'll have to, I tried here first because the trust is full of volunteers and it could take ages to get a reply

13 hours ago, druxey said:

The 'broad arrow' mark was the stamp on things that were Government property.

Yeah I thought of that but it's a finer arrow and doesn't make sense with the number above

3 hours ago, twintrow said:

10.6 and 10.7 Degrees off N ?   That many degrees swing?   Would seem someone in the Fort would know.  The Docents are usually well informed on all things fort.

 

Tom

We considered that when we were there but it can't be degrees because the three that show 10.6 are at different angles and the way they were mounted allowed 360 degrees of swing, the site is unmanned so there's no-one to ask and the only sign shows a little about the guns and how they mounted but nothing else.

1 hour ago, Hubac's Historian said:

Perhaps a measurement above sea level?

It can't be height above sea level because it's more like 10.6mtr than 10.6ft and we used imperial measurements back then

 

I also considered range to an inland point in that direction but that made no sense either

[Mark P]

Greetings everyone;

 

10.7 and the others are very precise measurements,  and as the possibility that they refer to compass alignments seems to have been unlikely,  could it be that they are degrees of elevation for the barrel of a later 19th/20th century gun to hit a target at a certain distance. 

 

All the best,

 

Mark P

 

 

[Bedford]

Don't know about that, we considered that it might be the minimum elevation to clear the fort. I've put the question to National Parks as they own the site so we'll see what they come back with.

[trippwj]

What is the date for the emplacements - do they date from 1790 or are they later (not that I know anything to illuminate the issue, just curious).

 

If one were to speculate, and have no relevant knowledge, one might (okay, I might) postulate the use of the numbers to indicate the assigned gun commander.  It looks like the 10.6 are all close together, while 10.7 & 10.8 are physically separate.

 

Or, it could be graffiti carved at some later date.

 

I have some free time this weekend (honey-do list permitting) and will do a wee bit of digging.

 

 

[geoffs]

FIrst fortifications on Middle Head were started in 1801.

[Canute]

It could be the magnetic variation between true north (map north) and magnetic compass north. The magnetic north pole is not at the true north pole so compass calculations have to make adjustment for that. I vaguely remember the variation on the US West Coast as being -14 degrees or so, so 10.6 in Australia is in the ballpark. Ship and aircraft navigators had to take it into account doing their work. The modern GPS systems do it automatically now. Paper maps for these kinds of navigation used to have lines of variation printed on them. I haven't looked at one in 20 years, so I don't know if they still do.

I was a rated Navigator in the USAF, but spent most of my time in F-4s, but we still did those types of calculations during mission planning.

[Backer]

My idea,

There are at least 3 locations in the bay with cannon positions.

Maybe it is the number of a(cannon) battery. A battery may consist of one or more guns. Therefore 3 times the 10.6 and one the 10.7 and 10.8. 

And if it then comes from WW2. The upward arrow can signify as anti-aircraft guns.

But as I already said. That is my idea

 

[Bedford]

It's not going to be graffiti because they are perfect squares carved into the rough cut sandstone and the new rebated surface is perfectly smooth, numbers and arrows are very precise and uniform in style and size.

 

The true north idea is interesting but then the fort never traveled and the guns would have been sight aimed in those days, not over the horizon like these days.

 

They must have been paranoid because there are gun emplacements all around the harbour, it would be interesting to check out all of them and see what they have

Edited August 31, 2018 by Bedford

[Altduck]

Might these have been the 6th, 7th and 8th batteries of the 10th Division or Regiment of Australian shore defense or something like that?

[Beef Wellington]

Do you happen to have a photo of the marking, there may be some additional context there?

[lehmann]

Does it look like this?  https://en.wikipedia.org/wiki/File:Old_Northern_Rd_convict_workgang_carving.jpg.  A bit of a discussion on this at https://en.wikipedia.org/wiki/Broad_arrow:  scroll down to "Australia".

 

On the page https://en.wikipedia.org/wiki/Benchmark_(surveying) there is this comment:

The terms "height" and "elevation" are often used interchangeably, but in many jurisdictions they have specific meanings; "height" commonly refers to a local or relative difference in the vertical (such as the height of a building), whereas "elevation" refers to the difference from a nominated reference surface (such as sea-level....

So, the numbers may refer to some other elevation benchmark, not sea level.

 

As another option:  At: https://en.wikipedia.org/wiki/Survey_marker

Geodetic survey markers were often set in groups. For example, in triangulation surveys, the primary point identified was called the triangulation station, or the "main station". It was often marked by a "station disk" (see upper photo at left), a brass disk with a triangle inscribed on its surface and an impressed mark that indicated the precise point over which a surveyor's plumb-bob should be dropped to assure a precise location over it. A triangulation station was often surrounded by several (usually three) reference marks (see second photo at left),^[5] each of which bore an arrow that pointed back towards the main station. These reference marks made it easier for later visitors to "recover" (or re-find) the primary ("station") mark. Reference marks also made it possible to replace (or reset) a station mark that had been disturbed or destroyed.

 

[popeye2sea]

What is the height of the wall at those points?  10.6, 10.7 ft.?  

 

Regards,

[Bedford]

11 hours ago, Altduck said:

Might these have been the 6th, 7th and 8th batteries of the 10th Division or Regiment of Australian shore defense or something like that?

This is possible but to have 4 guns in one bunker, 3 in one battery and one in another seems unfeasible 

10 hours ago, Beef Wellington said:

Do you happen to have a photo of the marking, there may be some additional context there?

No, we were both trying to work it out and didn't think to take a pic DOH!!! slapping the back of my own head!

10 hours ago, lehmann said:

Does it look like this?  https://en.wikipedia.org/wiki/File:Old_Northern_Rd_convict_workgang_carving.jpg.  A bit of a discussion on this at https://en.wikipedia.org/wiki/Broad_arrow:  scroll down to "Australia".

 

On the page https://en.wikipedia.org/wiki/Benchmark_(surveying) there is this comment:

 

So, the numbers may refer to some other elevation benchmark, not sea level.

 

As another option:  At: https://en.wikipedia.org/wiki/Survey_marker

 

 

Some interesting reading there but no real answer, The arrow did not have a dot at its tip, both sides joined at the tip, and the number is above the arrow in stead of below.

1 hour ago, popeye2sea said:

What is the height of the wall at those points?  10.6, 10.7 ft.?  

 

Regards,

Again, possible but they would have 10'7" which would make 10.6 feet approx. I can't see them decimalising an imperial measurement.

 

I may have to pay and do a tour but they don't do them very often.

[Backer]

16 hours ago, Bedford said:

They must have been paranoid because there are gun emplacements all around the harbour, it would be interesting to check out all of them and see what they have

This is to fire at the enemy with crossfire if he wants to do a landing in the harbour.

1 hour ago, Bedford said:

This is possible but to have 4 guns in one bunker, 3 in one battery and one in another seems unfeasible

Is possible. Already seen on parts of the Atlantic wall (German)

This part of the world is full of bunkers and forts. From the 17th century to WW 1 and WW2.  You name it, we have it. (unfortunately.....)

 

ps,

I hope we find the answer. I am very curious about it.

[John Allen]

Could it be the maximum rotation of the gun left or right in meters, looking at some civil war batteries in local forts guns that traveled on a round steel rail could not move 360 degrees but had stops at maximum rotation. This is probably a very stupid answer but your down to throwing darts.

 

It is a conundrum and when you find the answer let us know it is probably a very simple answer.

 

 

[trippwj]

Too me, the intriquing aspect is the decimal - not a common notation in the late 18th century.  Likewise, at that time, any measurements were imperial (feet and inches) not metric or even decimal feet.

 

Compass bearings were in degrees, minutes, seconds, not decimal.  Also not really needed for a fixed battery.

 

 

 

[Bedford]

17 hours ago, John Allen said:

Could it be the maximum rotation of the gun left or right in meters, looking at some civil war batteries in local forts guns that traveled on a round steel rail could not move 360 degrees but had stops at maximum rotation. This is probably a very stupid answer but your down to throwing darts.

 

It is a conundrum and when you find the answer let us know it is probably a very simple answer.

 

 

No stupid answers, like you said we are throwing darts at this point, blindfolded!

16 hours ago, trippwj said:

Too me, the intriquing aspect is the decimal - not a common notation in the late 18th century.  Likewise, at that time, any measurements were imperial (feet and inches) not metric or even decimal feet.

 

Compass bearings were in degrees, minutes, seconds, not decimal.  Also not really needed for a fixed battery.

 

 

 

Exactly, I just hope I can get an answer from NPWS but I'm not holding my breath, if it ain't about native wildlife or vegetation it's not very high on the list of priorities for the New South Wales National Parks and Wildlife Service. 

[mtaylor]

Those aren't some kind of survey markers are they?   Are they well weather worn like the rest of the fort?   

[Bedford]

Yeah Mark I'd say they are of similar age

[AndrewNaylor]

Range to a know spot What size guns where mounted there? A know range to a known point at 45' would be a very useful bit of information 

[Bedford]

12 hours ago, AndrewNaylor said:

Range to a know spot What size guns where mounted there? A know range to a known point at 45' would be a very useful bit of information 

I've considered that, measured it out on google maps and there's nothing of interest in that range and I doubt the guns would have had a 10.6 mile range in those days.

[John Allen]

May have nothing to do with nothing, but if that fort was used thru a century and a half or more dating the emplacements might lend a clue. Were they original revamped in the late 1800s, changed during World War I, refitted and changed for different guns in WWII.

 

There's a local fort here that had gun emplacements reconfigured from Civil War war to WWII?

[ebony678]

ask the folks at this site

 

https://cdsg.org/

[Captain Poison]

15 hours ago, Bedford said:

I've considered that, measured it out on google maps and there's nothing of interest in that range and I doubt the guns would have had a 10.6 mile range in those days.

No miles,kilometres..Maybe the marks were made in WWll. It can also be the diameter of the battery base.

Edited September 4, 2018 by Captain Poison

[Bedford]

Even in WW2 we still used imperial measures and those emplacements weren't used in WW2, also that late in history they just stuck signs up, these marks are very nicely carved into the sandstone.

 

We may have to wait until mid October to get an answer, we are doing a guided tour of the beehive casements in the base of the cliff below these gun emplacements and hopefully the guide will know.