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Re: Board of Trade exam, 1880s
From: Greg B
Date: 2013 Dec 27, 14:02 -0500
From: Greg B
Date: 2013 Dec 27, 14:02 -0500
Paul,
It sounds a little odd that the Sumner method would not yield the same accuracy.
As I understand the process it goes like this:
Sumner was sailing for several days with no sun / star sights and was unsure of his position
so he took a sun sight when he got a brief look at the sun so he could plot a longitude - but
since his latitude was uncertain he tried a latitude 10' higher than his DR and again with 10' lower
the 3 points formed a straight line and the line was really a LOP. Sumner later discovered if
he solved another line with a different body using the same latitudes as in the first problem
where the two lines crossed would be your 'exact position' . So if you have two nicely placed
bodies you should literally get X marks the spot. I also suppose that if you have 3 well placed
body's (like optimum for St. Hill) you nail it even better. Do you by any chance have the details of the
problem-so I could try it out? I think that doing Sumner first would give way too much information
and serve as a "sanity check" for your other work. Just my $0.02
~Greg
On 12/27/2013 12:54 PM, Paul Hirose wrote:
It sounds a little odd that the Sumner method would not yield the same accuracy.
As I understand the process it goes like this:
Sumner was sailing for several days with no sun / star sights and was unsure of his position
so he took a sun sight when he got a brief look at the sun so he could plot a longitude - but
since his latitude was uncertain he tried a latitude 10' higher than his DR and again with 10' lower
the 3 points formed a straight line and the line was really a LOP. Sumner later discovered if
he solved another line with a different body using the same latitudes as in the first problem
where the two lines crossed would be your 'exact position' . So if you have two nicely placed
bodies you should literally get X marks the spot. I also suppose that if you have 3 well placed
body's (like optimum for St. Hill) you nail it even better. Do you by any chance have the details of the
problem-so I could try it out? I think that doing Sumner first would give way too much information
and serve as a "sanity check" for your other work. Just my $0.02
~Greg
On 12/27/2013 12:54 PM, Paul Hirose wrote:
While looking for something else on the Web, I came across a 1882 study guide for the Board of Trade mate and master examinations. For the second mate exam, the candidate would be expected to "work a day's work complete, correcting the course for deviation, leeway, and variation. He will be required to find the latitude by meridian of the sun [sic], and also the longitude from a given departure by parallel sailing... and to find the longitude from altitude of the sun by the usual methods." A first mate was expected to find "the ship's position by Sumner's method by projection." "Candidates are expected to bring their answers to all problems within, or not to exceed, a margin of one mile of POSITION from a correct result, with the exception of the ship's position by Sumner's method, where a margin of 2 1/2 miles may be allowed." "The Sumner Problem (Exn. 6) must on no account be given out to any of the grades on the first day of the Examination, but should be the commencement of the Candidate's work on the second day, and on completion of this problem the Candidates for Masters' Certificates should proceed with the problems on Paper Exn. 7." There is no explanation for this restriction. Maybe working the Sumner problem first would make the other problems too easy? Table of contents: http://books.google.com/books?id=5zoIAAAAQAAJ&pg=PA175 --
