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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Definition of estimated position?
From: Paul Marcuzzo
Date: 2004 Sep 26, 16:26 -0400
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Good afternoon, well as I sit here and wait for hurricane Jeanne to abate some more I thought I'd try and clean out some email.  I saw your post and thought I'd comment.  I am a master instructor with the Coast Guard Auxiliary and I love to teach navigation when I have the time.  To get your estimated position you draw your LOP first, you then take take a perpendicular line from the LOP through your DR position for the time of the LOP.  Draw your line and then your EP is that intersection on the LOP.   I don't know how much trust I'd put into it, but it sure better than nothing, specially if the weather is a bit nasty out.   If my explanation is as clear as mud let me know and I'll try to do a better job.  I am much better with PowerPoint :-)

Fair winds & following seas !

Paul Marcuzzo

Flotilla Commander

Flotilla 98 - Charlotte Harbor, FL

Visit us at The Flotilla 98 Web Site

-----Original Message-----
Sent: Sunday, September 26, 2004 3:57 PM
Subject: Re: Definition of estimated position?

on 9/26/04 11:45 AM, Russell Sher at eastview{at}MWEB.CO.ZA wrote:

A navigational problem in the Jan/Febr. 2004 edition of Ocean Navigator Magazine (#135) posed a question which involved a navigator shooting the sun to obtain an LOP. Since there is only one LOP there is therefore no fix, but the one of questions asked is ‘What is the Estimated Position?’ I imagine that it is the position plotted on the LOP as being the closest from the DR. Does anyone agree?

Obviously in Coastal navigation, the estimated position is typically the position calculated from Course steered, log reading and taking tidal streams or current into account, but here the context is different.

(You can access the problem at -  www.oceannavigator.com <http://www.oceannavigator.com/>  (look under ‘browse by issue’  - choose jan/feb 2004, select the nav problem )

regards

Russell

Russell,
I agree, but only if the DR is based upon one's best guess of course and speed made over the ground. If course and speed are not equally in contention, then the better known one should weight the EP towards it, and the line going from the DR to the EP may not be exactly perpendicular to the LOP.  This question was discussed to exhaustion a few years ago.  Confusion bore from the fact that even the same edition of Bowditch will have two different definitions of EP, and that air and marine navigation have different customary meanings for DRs and EPs.  It remains an il-defined matter.

Ken Gebhart

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