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Everyone seems to agree that the main reason limiting the accuracy
of altitude sights (and their reliability!!) is the uncertainty of
the dip (and of refraction near the horizon).

Recently we learned of the cases when abnormal refraction causes
the errors of 10' order, which can really endanger the ship.
And there seems to be no way to correct these errors, or even to
know that they occur.

This brings again the question about dip-meters, the question which
was discussed a lot in the past. But I found something new, see below. I
repeat some points:

a) A Russian 1970 handbook for commercial vessels strongly recommends to
ALWAYS use the dip meter. I can concude from the book that this was a
standard equipment in 1960-s or 1970-s on Soviet ships.
I recently bought another textbook, "Celestial Navigation" of 1979 (in
Russian)
oficially approved by the gov't for commercial seamen's schools.
It has a chapter on dip-meters, a drawing of a dipmeter called N-5,
(Naklonomer-5, Dip-meter-5 in Russian).
together with instruction of use and correction. I can scan and post the
picture and the Russian pages if anyone is interested.

b) Apparently it was differently in the West. XX century English
navigation manuals do not even mention the device.
The only XX century mentioning in English literature is the article of
Shufeldt,
Precition Celestial Navigation Experiments of 1962.
He tested what he calls "Gavrisheff's dip-meter" and strongly approves it.
Today I found on the Internet an original report of Shufeldt,
which was previously classified:
http://www.math.purdue.edu/~eremenko/Navigation/shufeldt.pdf
The copy is very bad and some places are non-readable.
I have a better copy from the Journal of Navigation 1962.
But the photos are very bad in both copies.

However, the original report I found today has one substantial difference:
A PICTURE OF THE DIP-METER EXPLODED. And of good quality! It is not a
photo but a drawing.
See the link above, last page.

If I had a home workshop like Bill Morris, I would certainly attempt to
make one:-) Does not look super-complicated: two prizms a micrometer
screw and an arc of just few degrees.

c) Let me add that I've never seen the real thing, even a good photo.
Never found on e-Bay. I specially inquired the Russian sellers:
they have never heard of this.

The dipmeter used by Shufeldt differs from its Soviet counterpart,
though the name "Gavrisheff's dip-meter" (described by Shufeldt) sounds
definitely Russian:-) The older Russian book has a different name:
"Naklonomer Kavraiskogo", Kavraiski is apparently the designer name.

All this is somewhat strange. Both Shudeldt and Russian textooks strongly
approve the devise. Why it was not commonly made/used?
Why did not sextant makers produce them? Looks like a much more useful
thing at sea than an artificial horizon...


Alex.

   

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