# NavList:

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

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Re: Advance LOP of High Speed Vessel
From: Bruce J. Pennino
Date: 2012 Nov 14, 18:03 -0500
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Hello:

My fundamental question was " How do I know what length scale to use when advancing an LOP 51 NM on a universal plotting sheet?  Do I need to use vectors etc?

Thank you, everyone.

Byron....you got it right.  I took out a nautical chart and looked at the distance scale and carefully measured the distance between lines of latitude and longitude.  This chart  is of course a Mercator Projection...I remembered that from somewhere. The vertical scale , obviously to me now , is 1 minute of arc per NM AND the horizontal distance scale is the same!  That, I now understand, is the great beauty of the Mercator projection. From this,all angles are true for setting a course. AND with the Mercator projection the vertical/latitude scale is the distance scale, just as it says in all the CN books!  Use the vertical scale for minutes, toward or away, but this is also the distance scale. Maybe I'm not explaining this clearly. So I looked carefully at  a  universal plotting sheet and .......drum roll please....the light in my head goes off that this is just another Mercator projection . So use the vertical scale...it is that simple says Byron, and now me.

For my chart 60 minute of latitude = 60 NM = 2.75 inches.  Linear/distance scale is 1 inch =21.8 NM . Sometimes the obvious takes a while.

Bruce

----- Original Message -----
Sent: Friday, November 09, 2012 12:24 PM
Subject: [NavList] Re: Advance LOP of High Speed Vessel

Byron: Keep it simple, Take the first LOP on board the ship, DR.the ship on the chart, throw the LOP parallel to it's self off the ship at the next sight. DR. will include each change of course and speed between each sight. Did I miss-understance the problem?
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