Author Topic: Sometimes, even the Royal Navy gets it wrong!  (Read 6590 times)

Hugh Westacott

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Sometimes, even the Royal Navy gets it wrong!
« on: June 02, 2013, 07:13:10 AM »
I'm deeply interested in the history of the Royal Navy especially in the pre-steam era. Ive been re-reading Memoirs of a Fighting Captain by Admiral Lord Cochhrane who was probably the most dashing and successful frigate captain during the Napoleonic wars.

He recounts that when, as captain of the Pallas in the summer of 1805, he was escorting a convoy of merchantmen from Portsmouth to Quebec, he discovered that the ship's compass was inaccurate by 13.5°. An investigation revealed that the binnacle in which the compass was housed had been secured with iron instead of copper bolts. Cochrane diverted the convoy to Halifax to get the bolts replaced in the dockyard but this request was refused on the grounds that authority would first have to be obtained from London.

As Cochrane puts it 'To this I replied, that if such were the case, the Pallas should sit with the convoy at Halifax whilst they communicated with the Admiralty in England for that on no account should she enter the Gulf of St Lawrence until our compass was right. The absurdity of of detaining a convoy for six months on account of a hundredweight of copper bolts was too much even for dockyard routine, and the demand was with some difficulty conceded.'

Hugh

Barry G

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #1 on: June 02, 2013, 10:36:38 PM »
Hugh, a simple change of accents and you could be
 talking about the United States Navy!

Barry
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Lyle Brotherton

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #2 on: June 03, 2013, 09:29:42 AM »
...and to prove the point Barry :)

A tale was given to me by a more recent mariner, who back in the 1970’s was on-board a vessel being operated by the US Navy in the Java Sea, one of the waters of the East Indian Archipelago. The ship’s entire electronic navigational systems had entirely failed and it needed to return to the East Coast of the United States post haste. The Captain, after discussions with the navigation officer, made the decision to navigate using the ship’s compass, sextant and their marine charts.



This sextant had been manufactured in the 60’s by B. Cooke & Son Ltd of Hull, England. A business was founded in 1863 by Bernard Cooke who was a Clockmaker and Optician.

Using land reference points on Java to confirm location and fix the ships position the navigator was noted that there was a discrepancy of few Latitudinal seconds, when sighting the celestial objects with the sextant above the horizon to create the position lines on his nautical charts. As the ship progressed north towards Borneo he was able to continue to fix the ship’s location using land reference points and observed that this discrepancy, albeit small and within the limits of safety for open sea navigation changed with the time of day.

He realised that during the day, especially at noon when the ambient air temperature was at its highest the discrepancy was at its maximum and at night, there was no discrepancy and examining the sextant the calibration arm, with a vernier scale is made of brass for which the coefficient of expansion is considerable. Thereafter he took reading from the air-conditioned bridge and there were no further inconsistencies.
« Last Edit: June 03, 2013, 10:07:05 AM by Lyle Brotherton »
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Barry G

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #3 on: June 03, 2013, 05:59:39 PM »
Lyle, and how many oarsman did it take to move this ship?

Barry
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Callum

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #4 on: June 05, 2013, 01:53:59 PM »
Have you actually used this sextant Lyle? (Presume it's your hand holding it in  the photograph)

Lyle Brotherton

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #5 on: June 11, 2013, 09:09:23 AM »
Yes and Yes Callum.

People who I met during the research of the UNM would often give me navigational tools they had either once used or inherited, and this is such an example. Geoff Summers MBE (one of the world’s most accomplished polar travellers who has crossed Antarctica by its greatest axis) first introduced me to a sextant designed for use in WWII Bombers

There is nothing complicated about a sextant, it just looks complicated ;) Simply, it is a device that measures the angle between two objects.

The first task you learn in using a sextant is to measure the Sun’s altitude above the horizon at a specific time of day and it is actually very straight forward to do this.

Looking at my photo you will see lots of index shades (coloured filters) in front of the mirrors, you move them all across so the completely black out you view thru the telescope so you don’t damage your eyes with the Sun.

Now standing and facing the Sun with the sextant in your right hand, with your left hand on the index arm, you look through the eye piece at the horizon and move the index arm until the sun is visible through the two mirrors and index shades (you remove them, one by one, until you can see the Sun, a green ball against a dark green background). Rocking the entire sextant from side-to-side so that the sun’s image travels in a half-arc. Now, adjusting the index arm to bring the sun’s image down to just touch the horizon and you can read the sun’s altitude from the scales on the sextant.

There are two scales on the sextant. The scale on the frame is called the “arc,” while the scale on the index arm is the “vernier.” Each division of the arc equals one degree. Each division of the vernier equals two minutes (2'). To read the number of degrees, you find the lines on the arc which are closest to the zero mark on the vernier. The zero mark is usually somewhere between two lines. The correct arc reading is always that of the lower value, i.e., the line to the right of the zero mark and to read fractions of a degree, you find the division of the vernier which is in alignment with a division of the arc.

You now can refer to your Navigation Tables to identify your exact latitude.

I also own what I believe is one of the first baseplate compasses, which were constructed in the battlefields of Normandy by German Panzer tank crews during WWII. The bocage created a unique theatre where armoured close quarter combat played out and micronavigation was essential, in determining exactly where you were in relation not only to the enemy but your own troops. The German Army were masters of Battlefield Situational Awareness. These compasses differ from the earlier Swedish models accredited to the Swede Gunnar Tillander in 1928 and resemble much more the type we use today. It was given to me by a former Panzer Tank commander and I in turn gave it to my great buddy, Keith Lober, former Emergency Services Director of Yosemite SAR, USA and TL who collects WWII memorabilia.
“Opinion is the medium between knowledge and ignorance” - Plato

Callum

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #6 on: June 11, 2013, 10:14:31 AM »
Like most new things Lyle, daunting to the uninitiated. You make it sound very straight forward, I presume the difficult part is the readings and corrections needed for the Navigation Tables, which I have some experience of from sailing.

Pete McK

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Re: Sometimes, even the Royal Navy gets it wrong!
« Reply #7 on: June 22, 2013, 05:32:00 PM »
It's a big item for your rucksack ;)