Equipment > Compasses

Sometimes, even the Royal Navy gets it wrong!

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Hugh Westacott:
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:
Hugh, a simple change of accents and you could be
 talking about the United States Navy!

Barry

Lyle Brotherton:
...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.

Barry G:
Lyle, and how many oarsman did it take to move this ship?

Barry

Callum:
Have you actually used this sextant Lyle? (Presume it's your hand holding it in  the photograph)

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