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
From: Peter Hakel
Date: 2009 Dec 13, 16:30 -0800
Perhaps you can give us a simple example that will illustrate things better.
Input at time1: LOP1 only (i.e. no other information is available to establish EP1)
Input at a later time2: LOP2 only (since there is no EP1 then you don't have DR2 either)
Input: course and speed (made good)
Task: Establish a fix or an EP at time2 from the above data.
What is the best way of solving this problem, if a running fix is not appropriate?
I agree with you that if you do have an EP1 then doing a running fix is not the best, precisely for the reasons you gave. However, it is my understanding that the running fix method is not meant to be used in such a case in the first place. Instead, it is a substitute for the preferred two simultaneous and crossing LOPs, for example during the day when only the Sun is visible. As I said in #11122, the two different methods are applicable to two different problems, so they both have their area of purpose.
Peter Hakel
From: John Karl <jhkarl@att.net>
To: NavList@fer3.com
Sent: Sun, December 13, 2009 3:23:33 PM
Subject: [NavList 11128] Why Not To Teach Running Fixes
My 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 these two
assumptions?? Can anyone justify them??
Ah, the traditions of the sea.
JK
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From: Peter Hakel
Date: 2009 Dec 13, 16:30 -0800
John, I am now getting a little confused. Do you disagree with my post #11122?
Perhaps you can give us a simple example that will illustrate things better.
Input at time1: LOP1 only (i.e. no other information is available to establish EP1)
Input at a later time2: LOP2 only (since there is no EP1 then you don't have DR2 either)
Input: course and speed (made good)
Task: Establish a fix or an EP at time2 from the above data.
What is the best way of solving this problem, if a running fix is not appropriate?
I agree with you that if you do have an EP1 then doing a running fix is not the best, precisely for the reasons you gave. However, it is my understanding that the running fix method is not meant to be used in such a case in the first place. Instead, it is a substitute for the preferred two simultaneous and crossing LOPs, for example during the day when only the Sun is visible. As I said in #11122, the two different methods are applicable to two different problems, so they both have their area of purpose.
Peter Hakel
From: John Karl <jhkarl@att.net>
To: NavList@fer3.com
Sent: Sun, December 13, 2009 3:23:33 PM
Subject: [NavList 11128] Why Not To Teach Running Fixes
My 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 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
