# NavList:

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

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LOP Accuracy.
From: Byron Franklin
Date: 2010 Jan 12, 07:57 -0800

VISUAL NAVIGATION and the LINE of POSITION. LACK OF PROPER EMPHASIS ON LOPS ACCURACY.
I am writing this to the Navlist because many of the members are teaching bad information that is in your curriculum, Publications and all forms of passing “how to”. What is been carried on from person to person and is Damage to accurate fixes as being taught by all schools and in Publications. This teaching is based on lack of knowledge and can be easily disproved by simple chart work.
Teaching all Lines of Positions are equal, placing the fix in the center if there is a triangle (cocked hat.) is so wrong it actually hinders a fix and distorts set and drift.
You understand that the radian rule (sixty rule) controlled each line, and close NAVAIDS gave Close Lines of Position to the observer while Far NAVAIDS gave FAR CLOSEST POINT APPROACH (CPA). While I was in the Navy I would be called upon to solve compass and fixing problems for other ships, I would teach the navigation personnel how to find compass error for them selves. Every one I taught used my teaching. What did I teach to get that best fix possible for any given NAVAID arrangement?
I would simply select two of the closer NAVAIDS with a good spread for my fix. The third would not be part of the fix, but an indicator of accuracy. The two closes LOP. Intersection would be the best fix possible. The third told me how accurate and gave me compass error and correction.
The base to NAVAID selection, don’t do the math, but to look at the CHARTED NAVAIDS knowing that one NAVAID three times the charted distance of another closer NAVAID will have a closest point of approach CPA. Three time the distance of the closer. There are other factors of geometry that can slightly benefit the fix accuracy, but you can quickly select the best fix possible, using this simply idea will greatly improve fixes and finding a true “SET and DRIFT You and all schools and publications, influence new people to not get the best fix and set and drift, prevents this proven technique and has overwhelm a change that will improve visual navigation by many yards, sounds unimportant? But it is that few yards that make the difference,especially to the Navy three minute fixes in danger waters and compairing with the GPS position. This may cause you a little chart work or better, a little sea time. The proof of this technique, use a chart or maneuvering board, at random, place three NAVAID with you in the center or some where on the chart. Find the true bearings to each of the NAVAIDS. Add or subtract some value (one half/ one/ or ¼ degree (4 degrees will show better) to the true bearings. Replot, inspect, the difference between the center of the triangle and your true position and the closer two intersection of the selected fix NAVAIDS. The Navy and other institutions teach from the same book, with the same misinformation. I am going to try change that. Will the membership take the time to evaluated and back me? The drawing below may convince you. Will you take this to your schools and boating club to correct this fault? Works with magnetic compass also.
the difference between the center of the triangle and your true position. Inspect the difference
Ex Example.

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