NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Why Not To Teach Running Fixes yes
From: Joel Jacobs
Date: 2009 Dec 14, 09:01 -0500
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
From: Joel Jacobs
Date: 2009 Dec 14, 09:01 -0500
I will venture my opinion in answer to John's query, others may feel
differently.
First. John's ignores the presence of an experienced Navigator who would examine the positions that differed from where he thought the position should be so that he would reject them ab initio.Lu Abel just did that by explaining and questioning the mathematics of John's plot in his post, NavList 11142, which I thought was worthwhile reading. Also Peter Hakel's 11135 is also a good read. Interestingly, John Karl's answers another of Peter's posts in 11133, and seemingly makes some of the points that you will find in this post which are used against John's argument here.John's second assumption is to presume that a procedure that is discussed in such texts as Bowditch, McKnight's, Dutton's and taught at the maritime academies, and has inured the passage of time is faulty.Thirdly, his premise rests on crossing a DR LOP with an a second DR LOP and considering it a "Fix" which no Navigator would do. To begin with a running fix is not a Fix, and no "track is completely accurate", but is representative of the estimated course and distance traveled adjusted for offsets. Under the best of circumstances such as using EP's, they are always considered estimates as well. Read below.
There is no such thing as a pure RFIX (Running Fix not to be confused with
RAFIX, Radar Fix). It is a misnomer that has been brought forward as a historic
aberration. The navigation texts and the old Manuals of Navigation would
require that an RFIX be crossed with a third line to gain the precedence of
a "Fix" which John recognized. So I don't know why he stated
the idea that what he was proposing was a "Fix". In traditional
piloting or navigation the advance of any LOP to cross with
another is never considered a "FIX". And the third line elevating it
to Fix status would have to be from a reliable source such as CelNav, Loran C
(being discontinued), Radar Range and others of that level of
reliability.
From my point of view, John's illustration is based on accentuated
course errors for the purpose of illustrating his point. In the real world,
the Navigator or CO would first judge the reliability of such an
assumption, and if he felt the probability was unlikely based on all other
factors, he would reject it and solve for his estimate of the most
probable position, the size of which will vary with his judgment as to the
reliability of the data used. IMO, there is no substitute for good judgment, and
many skipper has saved the day when he empirically knew what to do. Again,
read Lu Abel's post, 11142 for testing the mathematics of the
illustration.
I know from my own experience the standard running fix procedure using
celestial bodies works because the next CelNav "Fix", or when in Loran C range,
electronic Fix or a landfall confirmed the EP, and its worked for thousands
of mariners before me. One fundamental rule of "navigation" I learned,
is to use all the means available. Which means you could use soundings as part
of your estimates, and so you use the running fix when its all that you have
available. But we must keep in mind its limitations.
Hopefully other people such as Lu and Peter, had similar
experiences, and will come up with the current List of Fix
Preferences, and a better answer to John's question, which, in my
words, is why teach running fixes at all.
Joel Jacobs
----- Original Message -----
--From: John KarlTo: NavList@fer3.comSent: Sunday, December 13, 2009 6:23 PMSubject: [NavList 11128] Why Not To Teach Running FixesMy argument against running fixes has nothing to do with how they're
taught, but it does challenge why they're taught -- at all.
It has nothing to do with how the location DR2 was estimated. As long
as DR2 is found by combining relatively inaccurate data, and not by
forming a fix of a third LOP with LOP2, it is irrelevant what (or
which) estimates are included in DR2: speed, time, logged distance,
drift, current, averaged headings, the flight of birds, etc. I'm
talking about arriving at DR2 without a bona fide fix.
I pointed out that the concept behind the traditional running fix is
based on two ridiculous assumptions: the assumption that the estimated
DR track perpendicular to LOP1 is completely accurate while the DR
component parallel to LOP1 is completely without value.
I ask again, can anyone on the List refute these two
assumptions?? Can anyone justify them??
Ah, the traditions of the sea.
JK
--
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
