NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The Running Fix on an Ellipsoid
From: David Pike
Date: 2017 Feb 4, 12:33 -0800
Gary. What you say is true up to a point. Also, as far as I can see, the method suffers from the same problem as the traditional running fix, i.e. not knowing ones track and speed over the seabed exactly.
However, one ought to be able to enjoy a clever piece of mathematics for what it is, and begin looking for applications. We live in a World where almost everyone (me excluded!) has a smart phone, but relatively few are skilled with charts and dividers or 100% happy with the triangle of velocities. The value of Robin’s paper, as I see it, is that it wouldn’t take long for a young chap who was a whiz with a computer to produce a ‘App’ for a smart phone or laptop where you just typed in the times; celestial heights observed; the height of the observer; best guess at latitude, track made good, and distance run; plus a few other things depending how clever the app was and if it had an inbuilt almanac and you got out a lat & long. The method described in the paper could also cope with changes in course if you plotted them separately on graph paper; stuck on the required amount tidal flow at the end; and measured the mean track made good and distance run. DaveP
P.S. Had a great sail in TIKI on the Humber today. Four degrees centigrade, but bright sunshine and wind F3. Genny only, beam reach both ways. 30 minutes up river and 30 minutes down on the top of the tide. Not long but long enough for a couple of pensioners. No other pleasure craft sighted.
From: David Pike
Date: 2017 Feb 4, 12:33 -0800
Gary you wrote: Um... much ado about nothing. I read the paper and it is a whole lot easier to just advance the LOP to obtain the running fix. If your look at the diagram explaining the process it is simply showing the standard advancing the LOP to cross the second LOP. Remember, the first LOP is a line, and infinite set of points, that are advanced until one of those points intersects with the second LOP and that is exactly what the diagram shows if the entire LOP had been advanced the same intersecting point would have been found. If there is any greater accuracy to the complex mathematical process it is swamped by the normal uncertainty of the underlying celestial observations.
Gary. What you say is true up to a point. Also, as far as I can see, the method suffers from the same problem as the traditional running fix, i.e. not knowing ones track and speed over the seabed exactly.
However, one ought to be able to enjoy a clever piece of mathematics for what it is, and begin looking for applications. We live in a World where almost everyone (me excluded!) has a smart phone, but relatively few are skilled with charts and dividers or 100% happy with the triangle of velocities. The value of Robin’s paper, as I see it, is that it wouldn’t take long for a young chap who was a whiz with a computer to produce a ‘App’ for a smart phone or laptop where you just typed in the times; celestial heights observed; the height of the observer; best guess at latitude, track made good, and distance run; plus a few other things depending how clever the app was and if it had an inbuilt almanac and you got out a lat & long. The method described in the paper could also cope with changes in course if you plotted them separately on graph paper; stuck on the required amount tidal flow at the end; and measured the mean track made good and distance run. DaveP
P.S. Had a great sail in TIKI on the Humber today. Four degrees centigrade, but bright sunshine and wind F3. Genny only, beam reach both ways. 30 minutes up river and 30 minutes down on the top of the tide. Not long but long enough for a couple of pensioners. No other pleasure craft sighted.
