Kukri
Well-known member
I will start with a disclaimer - I think GPS actually is a good deal better than sliced bread. But being one of those people who carries around a Walker log and a sextant “just in case”, I thought I would see what happened to a good mechanical watch over a week.
Before Transit satnav, in the later 1980s, all yachts used a deck watch and the time signal to carry GMT. (Full size chronometers don’t work reliably on yachts or other small craft because the motion is too violent).
Before the time signal, yachts just used a deck watch. But the advice given to all vessels regardless of size was to carry one chronometer. or three, but never two, because if you have two, and they start to disagree, you won’t know which one is lying. Indeed the Victorian Admiralty used to issue one chronometer to each ship unless her Captain owned his own, in which case they issued two, so that he could have three!
Captain Fitzroy of HMS “Beagle” carried twenty-one chronometers, in their own cabin, with a full time watchmaker to take care of them, and when the “Beagle” got back to Falmouth after six years he was only a few seconds out, though he will certainly have recovered GMT by observation several times during the voyage.
I happen to have three navigational deck watches.
The one on the left is a Ulysse Nardin, bought by the Admiralty in 1940 (no, I don’t know how - there is space for a small book on how Swiss watch makers got their products to market during WW2 - but Ulysse Nardin were equal opportunity chronometer makers - they supplied the RN and the Kriegsmarine in equal numbers!)
The one in the middle is a Hamilton model 992B aircraft navigation watch supplied to the USAF in 1942. And the one on the right is an EMT (Edmond Massey-Tissot - also Swiss) supplied to the RN in the later 40s.
I added a Waltham “railroad watch” made in 1952 (US “railroad watches”, by Act of Congress, had to meet chronometer standards of accuracy, and were used for navigation by people like Hiscock and Tilman) and a couple of Ulysse Nardin wristwatches from the Fifties and Sixties.
After a week of being wound at the same time each day and otherwise left alone, this is what I got:
The Ulysse Nardin deck watch is away with the fairies and clearly needs a new balance spring - 6 minutes 50 seconds fast. The Hamilton is 43 seconds slow. The EMT is 90 seconds slow. The Waltham railroad watch is one minute 12 seconds slow, the Sixties automatic Ulysse Nardin wristwatch is one minute 45 seconds slow and the Fifties hand winding one (which has led a hard life, and is usually on my wrist) is five seconds fast.
Now, if we were navigating in the southern North Sea, at 53 degrees N, taking the three deck watches, discarding the one that is obviously wrong, and averaging the other two, the error in pure longitude would be sixty seconds in time, or fifteen minutes of longitude. At 53N. one minute of longitude is 0.6 of a nautical mile, so we would be (15 x 0.6) = 9 miles out, after a week, and it’s quite hard to be at sea for a week in the southern North Sea, (though I have come close...) so the result is acceptable before we add in sextant errors and more importantly observer errors in handling the sextant!
If on the other hand we were approaching Barbados, in 13 degrees N, after three weeks at sea, which is entirely possible, we would be 42 miles ahead of where we thought we were, which is a bit worrying!
With a radio time signal, of course, that error would have been picked up, and we would be at worst a mile and a bit “out”, which is quite acceptable.
On the whole, let’s stick with GPS - and hope for no lightning strikes!
Before Transit satnav, in the later 1980s, all yachts used a deck watch and the time signal to carry GMT. (Full size chronometers don’t work reliably on yachts or other small craft because the motion is too violent).
Before the time signal, yachts just used a deck watch. But the advice given to all vessels regardless of size was to carry one chronometer. or three, but never two, because if you have two, and they start to disagree, you won’t know which one is lying. Indeed the Victorian Admiralty used to issue one chronometer to each ship unless her Captain owned his own, in which case they issued two, so that he could have three!
Captain Fitzroy of HMS “Beagle” carried twenty-one chronometers, in their own cabin, with a full time watchmaker to take care of them, and when the “Beagle” got back to Falmouth after six years he was only a few seconds out, though he will certainly have recovered GMT by observation several times during the voyage.
I happen to have three navigational deck watches.
The one on the left is a Ulysse Nardin, bought by the Admiralty in 1940 (no, I don’t know how - there is space for a small book on how Swiss watch makers got their products to market during WW2 - but Ulysse Nardin were equal opportunity chronometer makers - they supplied the RN and the Kriegsmarine in equal numbers!)
The one in the middle is a Hamilton model 992B aircraft navigation watch supplied to the USAF in 1942. And the one on the right is an EMT (Edmond Massey-Tissot - also Swiss) supplied to the RN in the later 40s.
I added a Waltham “railroad watch” made in 1952 (US “railroad watches”, by Act of Congress, had to meet chronometer standards of accuracy, and were used for navigation by people like Hiscock and Tilman) and a couple of Ulysse Nardin wristwatches from the Fifties and Sixties.
After a week of being wound at the same time each day and otherwise left alone, this is what I got:
The Ulysse Nardin deck watch is away with the fairies and clearly needs a new balance spring - 6 minutes 50 seconds fast. The Hamilton is 43 seconds slow. The EMT is 90 seconds slow. The Waltham railroad watch is one minute 12 seconds slow, the Sixties automatic Ulysse Nardin wristwatch is one minute 45 seconds slow and the Fifties hand winding one (which has led a hard life, and is usually on my wrist) is five seconds fast.
Now, if we were navigating in the southern North Sea, at 53 degrees N, taking the three deck watches, discarding the one that is obviously wrong, and averaging the other two, the error in pure longitude would be sixty seconds in time, or fifteen minutes of longitude. At 53N. one minute of longitude is 0.6 of a nautical mile, so we would be (15 x 0.6) = 9 miles out, after a week, and it’s quite hard to be at sea for a week in the southern North Sea, (though I have come close...) so the result is acceptable before we add in sextant errors and more importantly observer errors in handling the sextant!
If on the other hand we were approaching Barbados, in 13 degrees N, after three weeks at sea, which is entirely possible, we would be 42 miles ahead of where we thought we were, which is a bit worrying!
With a radio time signal, of course, that error would have been picked up, and we would be at worst a mile and a bit “out”, which is quite acceptable.
On the whole, let’s stick with GPS - and hope for no lightning strikes!
Last edited:
