NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Advancing LOP's in surface Celnav.
From: Peter Hakel
Date: 2013 Mar 10, 12:51 -0700
From: Peter Hakel
Date: 2013 Mar 10, 12:51 -0700
Gentlemen,
Thank you both for the recap. The method described by Gary comes handy for T-Plotter users by keeping the AP where it originally was, which on a VSOP plotting sheet is likely to be at the center of the compass rose.
Using Jeremy's example, the navigator can plot this retarded LOP as follows:
1. Convert the requisite time interval into decimal hours (e.g. with time.xls, T = -0.2 hours)
2. Compute the original altitude and azimuth (e.g., with attached intercept.xls) disregarding vessel motion for now:
Ho = 29d 57'
AP Lat: N 30d
intercept: 3 nm Away
azimuth: 000
3. Enter this information into attached alt_move.xls and extract:
Ho adjusted: 30d 01'
4. Take this adjusted Ho from and reenter it into intercept.xls in cell E2; now we get:
intercept: 1 nm Toward
azimuth 000
5. Plot the retarded LOP using the original AP and updated intercept (which in this case also changed sign). Result:
Vessel latitude at 1830: N 30d 01'
Peter Hakel
From: Gary LaPook <garylapook@pacbell.net>
To: pmh099@yahoo.com
Sent: Saturday, March 9, 2013 5:44 PM
Subject: [NavList] Re: Advancing LOP's in surface Celnav.
Thank you both for the recap. The method described by Gary comes handy for T-Plotter users by keeping the AP where it originally was, which on a VSOP plotting sheet is likely to be at the center of the compass rose.
Using Jeremy's example, the navigator can plot this retarded LOP as follows:
1. Convert the requisite time interval into decimal hours (e.g. with time.xls, T = -0.2 hours)
2. Compute the original altitude and azimuth (e.g., with attached intercept.xls) disregarding vessel motion for now:
Ho = 29d 57'
AP Lat: N 30d
intercept: 3 nm Away
azimuth: 000
3. Enter this information into attached alt_move.xls and extract:
Ho adjusted: 30d 01'
4. Take this adjusted Ho from and reenter it into intercept.xls in cell E2; now we get:
intercept: 1 nm Toward
azimuth 000
5. Plot the retarded LOP using the original AP and updated intercept (which in this case also changed sign). Result:
Vessel latitude at 1830: N 30d 01'
Peter Hakel
From: Gary LaPook <garylapook@pacbell.net>
To: pmh099@yahoo.com
Sent: Saturday, March 9, 2013 5:44 PM
Subject: [NavList] Re: Advancing LOP's in surface Celnav.
Well, that's one way to advance an LOP. I posted the following method before that accomplishes the same thing without having to plot the lines. Using your example of 12 minutes at 20 knots with a relative bearing of 180 degrees, my table shows a correction of 4.2 minutes of arc (4.2 NM) (2 times the correction for 6 minutes) for the closest value in my table of 21 knots. ( If I had tabulated 20 knots then the results would exactly match yours of 4.0 NM.) My method has the advantage of allowing for the relative bearing being other than 180 or 0 degrees. You can compute your own table for any speed values you want. http://fer3.com/arc/img/121087.moo21.pdf http://fer3.com/arc/m2.aspx/Advancing-LOPs-for-precision-fixes-LaPook-feb-2010-g11994 http://fer3.com/arc/m2.aspx/errors-plotting-possiblepartial-fix-thereof-menti-LaPook-dec-2010-g15022 http://fer3.com/arc/m2.aspx/Advance-LOP-High-Speed-Vessel-LaPook-nov-2012-g21087 gl --- On Fri, 3/8/13, Jeremy C <jcaoy---com> wrote:
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: http://fer3.com/arc/m2.aspx?i=122751
File: 122760.intercept.xls
File: 122760.alt_move.xls