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+--- Thread: Old method to find the positions suggested by "Cloudy Weather" Johnson (/showthread.php?tid=227)
Old method to find the positions suggested by "Cloudy Weather" Johnson - Rumata - 05-19-2021
Greetings, gentlemen, ( I also posted the same on Sight Reduction thread)
I'm pretty sure that many of you are familiar with the method, old one, which I recently discovered for myself.
I refer to C.A. ("Cloudy Weather" Johnson's "Double Chronometer Method"). I found the copy of old book and read and tried to use this method. At first, it looks a little bit archaic, but as soon as you pay a little bit attention to quite straight forward rules everything became cushty ( East London's slang for "cool."). The method doesn't require noon sight and was developed for usage at cloudy weather when sun wasn't really available. I don't want to overload you with details, but the main principle is: you take two observations supposedly a couple hours apart. It may be DR and after some run- new position ( lat. and long) Using a few corrections the lat and long are adjusted and you got your position. The key correction table is Table II, which is originally came from Capt. Norie ' Tables. Also Pub.260 concerning Sun azimuth is used.
I'm not saying it is a magic bullet, but I found it interesting especialy considering the fact the British Navy extensively used it and the book had 34 reprints. before 1918. This method is also described in Captain Lecky's great book "Wrinkles in Navigation."
Anyway, just wanted to share it with you.
Thanks.
BTW, below you can see the basic rules to do it
1. Let two chronometer observations be taken at an interval of about 1.5-2 hours. Let the first be worked out with the Lat. DR at the time of observation:
2. Let the Lat Dr and Long. thus obtained be corrected for the nrun of the ship in the interval between the observations, and let the second observation be worked with this corrected latitude. Name these Longs. (1) and (2)
3. The bearing of the sun at each observation is to be taken from an Azimuth TAble.
4. Enter Table II ( in Johnson's book) with the Lat and bearings, and take from it two numbers (a) and (b) of which take the difference. or sum, according as the bearings are in the same or adjacent quarters of the compass. The difference of Longs divided by this difference or sum of (a) and (b) gives the correction for the second lat. And (a) and (b) multiplied by the correctness for latitude give the corrections for the two longs. Both Longs. should agree. zif not- it shows the corrections have been wrongly applied. A good safeguard against error., peculiar to this method only.
There are some additional nuances which I did not include in this basic rules. Just for general idea. :>:>