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    Re: A day's work in 1937 onboard the barque Alastor, revisited
    From: Lars Bergman
    Date: 2021 Dec 5, 13:23 -0800

    Brian,

    Thanks. I am not sure if I understand all of your questions, but I will try to answer a few.

    a. In the middle of the North Sea, you do not need your longitude immediately. The depth of the Dogger's Bank is no hinder for a vessel of Alastor's size. You could have used your DR latitude to reduce the time sight, but that being probably some 22 hours old. With such a small "cut" between azimuths an error in latitude makes quite an impact of the resulting longitude, so you want the best latitude available, and that is the nearest in time, i.e. the two hours away noon latitude.

    b. I do not know for sure that the log readings were taken at the time sight and at the noon sight, I just assumed that. Why the navigator used 10 miles instead of 9.2 miles I do not know, it could have been a known under-recording of the log, guessed tidal influence, or whatever.

    c. Yes, the "cut" is small. Either it was cloudy earlier or the navigator wanted to avoid too small altitudes. Altitudes less than 7° are not included in the altitude correction table. It is always a compromise between a good "cut" and a short "run" between observations. The better the cut the longer the run with its inherent uncertainty. At high latitudes you can never get a good cut in the winter, or late autumn, using the sun only. I certainly do not agree that it should have been a company requirement to record a noon position. I do not know the reason for the heading, it could have been an easterly wind preventing a more easterly course, or it could have be that they wanted a good offing from the Jutland coast, a difficult area in westerly winds.

    A steam tug would not be used on such a voyage, except for out of, or in to, a harbour. 

    Your interest in steam tugs would possibly be off topic in this forum, but your interest in time sights is indeed on topic.

    Lars

       
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