NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Teaching a Running Fix
From: Peter Hakel
Date: 2009 Dec 12, 19:51 -0800
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From: Peter Hakel
Date: 2009 Dec 12, 19:51 -0800
As a student I interpreted the running fix to myself in the following manner:
You were somewhere on the original LOP at the time of the sight. Take each point along the LOP and advance it by DR. The collection of these new possible positions is the LOP used in the running fix.
When plotted on a Mercator chart using the intercept method this amounts to constructing a LOP parallel to the original one. You can either shift the original LOP, or shift the AP - this makes no difference in this approximation.
Advancing the entire original circular LOP is a more complicated matter. The LOP can change shape and size; imagine doing a running fix with a Polaris LOP.
Peter Hakel
From: QMCM <byronink@netzero.com>
To: NavList <navlist@fer3.com>
Sent: Sat, December 12, 2009 5:24:56 PM
Subject: [NavList 11111] Re: Teaching a Running Fix
LU what a good job on the PP running fix. You hit all the points
perfect. I almost would take back what I wrote, You demostrated
everything.
On Dec 12, 4:03 pm, Lu Abel <lu...@abelhome.net> wrote:
> Joe:
>
> I've taught this many times. The way I explain it to my students is to
> tell them to imagine that at the time of the first bearing the sighted
> object suddenly clones. One of the clones stays in the original
> position. The other clone moves on exactly the same course and at
> exactly the same speed as the vessel. I demonstrate to them that the
> bearing to the moving clone stays the same as the vessel advances, but
> the position of the bearing line moves along with the vessel. You then
> take a second bearing back to the original object and cross the two.
> Most of them say the image of the clone of the lighthouse moving along
> with the vessel helps them understand the (not naturally intuitive)
> concept of advancing a line of position.
>
> In fact, I put this into a set of PowerPoints that won a national award
> from the US Power Squadrons. I can send you a copy off-line if you
> desire (or, if there is demand, I can post it in the archives)\
>
> I work in high-tech and have lived in high-tech areas (first Boston and
> now Silicon Valley) and my classes have always been a challenging
> combination of engineers and other way less mathematically proficient
> people. Teach currents? The engineers say "easy, it's vector math,
> let's go on to the next topic" while the others' eyes glaze over....
> So I've always found a challenge in explaining concepts (like running
> fixes) in ways that won't bore the engineers while helping get the
> non-engineers on board.
>
> Lu Abel
>
>
>
> joseph_schu...@rrv.net wrote:
> > A challenge, in the spirit of the intention of this list, which is the promotion of the use of traditional navigation techniques.
>
> > You're tutoring a small group of new navigators. Normal people, ranging in age from 12 to "retired."
>
> > Here's what they can do on a paper chart/map:
> > 1. Plot a track.
> > 2. Plot and label DR positions, using
>
> > distance = speed x time
>
> > 3. Plot and label a line-of-position to a visual object, understanding that it take two or more simultaneous LOPs to constitute a fix.
>
> > Your mission, if you choose to accept: close the schoolbook. Explain, in words your students can understand, the concept of a running fix.
>
> > No grades, no judgement. I'm interested in learning how you'd teach it.
>
> > Joe- Hide quoted text -
>
> - Show quoted text -
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You were somewhere on the original LOP at the time of the sight. Take each point along the LOP and advance it by DR. The collection of these new possible positions is the LOP used in the running fix.
When plotted on a Mercator chart using the intercept method this amounts to constructing a LOP parallel to the original one. You can either shift the original LOP, or shift the AP - this makes no difference in this approximation.
Advancing the entire original circular LOP is a more complicated matter. The LOP can change shape and size; imagine doing a running fix with a Polaris LOP.
Peter Hakel
From: QMCM <byronink@netzero.com>
To: NavList <navlist@fer3.com>
Sent: Sat, December 12, 2009 5:24:56 PM
Subject: [NavList 11111] Re: Teaching a Running Fix
LU what a good job on the PP running fix. You hit all the points
perfect. I almost would take back what I wrote, You demostrated
everything.
On Dec 12, 4:03 pm, Lu Abel <lu...@abelhome.net> wrote:
> Joe:
>
> I've taught this many times. The way I explain it to my students is to
> tell them to imagine that at the time of the first bearing the sighted
> object suddenly clones. One of the clones stays in the original
> position. The other clone moves on exactly the same course and at
> exactly the same speed as the vessel. I demonstrate to them that the
> bearing to the moving clone stays the same as the vessel advances, but
> the position of the bearing line moves along with the vessel. You then
> take a second bearing back to the original object and cross the two.
> Most of them say the image of the clone of the lighthouse moving along
> with the vessel helps them understand the (not naturally intuitive)
> concept of advancing a line of position.
>
> In fact, I put this into a set of PowerPoints that won a national award
> from the US Power Squadrons. I can send you a copy off-line if you
> desire (or, if there is demand, I can post it in the archives)\
>
> I work in high-tech and have lived in high-tech areas (first Boston and
> now Silicon Valley) and my classes have always been a challenging
> combination of engineers and other way less mathematically proficient
> people. Teach currents? The engineers say "easy, it's vector math,
> let's go on to the next topic" while the others' eyes glaze over....
> So I've always found a challenge in explaining concepts (like running
> fixes) in ways that won't bore the engineers while helping get the
> non-engineers on board.
>
> Lu Abel
>
>
>
> joseph_schu...@rrv.net wrote:
> > A challenge, in the spirit of the intention of this list, which is the promotion of the use of traditional navigation techniques.
>
> > You're tutoring a small group of new navigators. Normal people, ranging in age from 12 to "retired."
>
> > Here's what they can do on a paper chart/map:
> > 1. Plot a track.
> > 2. Plot and label DR positions, using
>
> > distance = speed x time
>
> > 3. Plot and label a line-of-position to a visual object, understanding that it take two or more simultaneous LOPs to constitute a fix.
>
> > Your mission, if you choose to accept: close the schoolbook. Explain, in words your students can understand, the concept of a running fix.
>
> > No grades, no judgement. I'm interested in learning how you'd teach it.
>
> > Joe- Hide quoted text -
>
> - Show quoted text -
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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
