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, 11:08 -0800
From: John Karl <jhkarl@att.net>
To: NavList@fer3.com
Sent: Sun, December 13, 2009 8:25:27 AM
Subject: [NavList 11116] Why Not To Teach Running Fixes
Ah, the traditions of the sea.
For all the talk on how to teach running fixes, here's my 2 cents
worth on why to not teach them at all -- they make no sense whatsoever.
The figure below shows that they operate under extremely ridiculous
assumptions: They assume that the estimated DR track perpendicular to
LOP1 is completely accurate and that the DR component parallel to LOP1
is completely without value. Can anyone on the List justify these two
assumptions??
I recommend using the Estimated Position (EP) concept shown in the
figure. It fully honors the new LOP2 while retaining the information
in the DR that is not contradicted by LOP2.
JK
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From: Peter Hakel
Date: 2009 Dec 13, 11:08 -0800
That's a very good point but I think that the running fix technique and the EP technique are solutions to two slightly different problems. In your picture you already have an EP1 which can be advanced by DR (in that case you really don't care about LOP1). The running fix is the next best thing when LOP1 is all you have and you really don't know just where along that LOP1 you really are. This corresponds to the running fix method ignoring the component parallel to LOP1, just as you said.
So the EP technique is indeed clearly preferable to running fix but it does require having more information on input. Ideally, a navigator should have that EP1 inferred from his previous work during the voyage. In less than ideal situations, when you only have LOP1 instead of EP1, the running fix technique can be used as a backup option.
Peter Hakel
So the EP technique is indeed clearly preferable to running fix but it does require having more information on input. Ideally, a navigator should have that EP1 inferred from his previous work during the voyage. In less than ideal situations, when you only have LOP1 instead of EP1, the running fix technique can be used as a backup option.
Peter Hakel
From: John Karl <jhkarl@att.net>
To: NavList@fer3.com
Sent: Sun, December 13, 2009 8:25:27 AM
Subject: [NavList 11116] Why Not To Teach Running Fixes
Ah, the traditions of the sea.
For all the talk on how to teach running fixes, here's my 2 cents
worth on why to not teach them at all -- they make no sense whatsoever.
The figure below shows that they operate under extremely ridiculous
assumptions: They assume that the estimated DR track perpendicular to
LOP1 is completely accurate and that the DR component parallel to LOP1
is completely without value. Can anyone on the List justify these two
assumptions??
I recommend using the Estimated Position (EP) concept shown in the
figure. It fully honors the new LOP2 while retaining the information
in the DR that is not contradicted by LOP2.
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
