We have a full-sized (each page is 11"x17") copy of the Itasca deck log. At the beginning of the log is a section entitled Instructions For Keeping The Ship's Log. It includes all the codes and scales to be used in keeping the log. TIGHAR's interpretations of the log are based on those instructions. I've attached scans of several of the scales including wind and visibility.
I think that there is still a question concerning the codes used in the Itasca deck log for recording the visibility and the force of the wind. The visibility table in the deck log preamble contained the values for a weather code dated 1921 and the values were changed in the 1930 weather code that was being used by Itasca for reporting the weather. The wind speed ranges for the Beaufort scale were also changed in 1923 to their current form, I posted that table before. We know that Itasca was using the newer weather code because the 1921 code used words instead of numerical groups. Here is a link to the
obsolete 1921 weather code.
I have attached excerpts from the deck log, the radio transcripts and from the 1930 weather code. I am also posting the entire 1930 weather code. You can see that the weather report sent out on July 1, 1937 at 1330 Itasca time encoded the weather recorded in the Itasca deck log for 1 p.m. on July 1st. The "9" in the fourth group is the code for the visibility which, according to the 1930 code, means greater than 30 NM and would be read as such by headquarters. But, if the preface to the deck log is correct, that "9" only indicates visibility greater than 20 NM. Which is it, 30 NM or 20 NM, you can't have it both ways. The weather code is for transmitting the weather unambiguously so a "9" can't mean 20 NM sometimes and 30 NM at other times.
Did the Coast Guard just continue to use obsolete deck log forms until the supply was exhausted but actually used the new coding for the information? Aside from the deck log preamble, does TIGHAR have any other source of information to explain this conflict, a statement from somebody in the Coast Guard in 1937 perhaps?
I have decoded the entire 6 group message so you can compare it yourself with the entries in the deck log entry.
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The 6001 1330 weather message decoded reads:
First group, 61008
6 = Friday (July 2, Greenwich date)
1 = Octant of earth 1 = (North latitude, 90° to 180° west)
008 =Latitude 00.8° N (Latitude rounded to 6 minute accuracy and reported as one-tenth of degree, the octant code makes it north)
Second group, 76700
767 = Longitude 176.7° W ( the octant code makes it greater than 90° W)
00 =GMT of observation is 0000)
Third group, 05201
05 = Wind direction = NE X E
2 = Beaufort force 2 = light breeze
01 = Current weather = Partly cloudy, 0.1 to 0.5 of sky covered
Fourth group, 10986
10 = Barometer = 29.83 (rounded to whole millibar if necessary)
9 = Visibility = objects visible at more than
30 NM86 = Temp= 86° F
Fifth group, 62254
6 = group identifier
2 = swell = low swell, long
2 = direction of swell = east
5 = predominant cloud type = alto stratus
4 = total cloud = 0.4 to 0.6
Sixth group, 20010
2 = temp difference = air temp. 3° to 6° warmer than the sea temp.
0 = ship's course = hove to (drifting)
0 = barometer tendency = steady
1 = past weather = variable sky
0 = form of upper cloud = no upper clouds
gl