NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: USCG Student Sample Problem #4
From: Peter Hakel
Date: 2013 Apr 27, 22:01 -0700
From: Greg Rudzinski <gregrudzinski@yahoo.com>
To: pmh099@yahoo.com
Sent: Wednesday, April 24, 2013 10:12 AM
Subject: [NavList] USCG Student Sample Problem #4
From: Peter Hakel
Date: 2013 Apr 27, 22:01 -0700
This #4 sample problem created by Greg Rudzinski provides a nice illustration of a couple of issues discussed here recently on NavList.
First is the importance of accounting for vessel motion in order to obtain the best attainable accuracy for the many-body fix. The first attached plot shows the three star lines plotted at their respective times forming a small triangle. In the second attached plot these LOPs were adjusted and the initial cocked hat tightens to a pinwheel as a result. Greg made the same plot in his original posting; in my plot the LOPs were shifted by recalculating the intercepts following the method presented by Gary LaPook ( change ~ time x cosine( azimuth - course ) ).
Second, in the upper part of the second plot we can see the EP of 3 hours after the tree-star fix, which was also shown in Greg's original posting. To that I added the DR-advanced LOPs for all three stars, which results in three separate traditional running fixes with a spread of several miles across the one Sun line. Given that the Sun and Dubhe azimuths are close to perpendicular to each other, the Dubhe running fix is very close to the EP. The third attached image shows this part of the plot in more detail.
Peter Hakel
First is the importance of accounting for vessel motion in order to obtain the best attainable accuracy for the many-body fix. The first attached plot shows the three star lines plotted at their respective times forming a small triangle. In the second attached plot these LOPs were adjusted and the initial cocked hat tightens to a pinwheel as a result. Greg made the same plot in his original posting; in my plot the LOPs were shifted by recalculating the intercepts following the method presented by Gary LaPook ( change ~ time x cosine( azimuth - course ) ).
Second, in the upper part of the second plot we can see the EP of 3 hours after the tree-star fix, which was also shown in Greg's original posting. To that I added the DR-advanced LOPs for all three stars, which results in three separate traditional running fixes with a spread of several miles across the one Sun line. Given that the Sun and Dubhe azimuths are close to perpendicular to each other, the Dubhe running fix is very close to the EP. The third attached image shows this part of the plot in more detail.
Peter Hakel
From: Greg Rudzinski <gregrudzinski@yahoo.com>
To: pmh099@yahoo.com
Sent: Wednesday, April 24, 2013 10:12 AM
Subject: [NavList] USCG Student Sample Problem #4
Here is my final USCG student sample problem ( #4 east longitude and north latitude ).
Fare well to the land of Oz and onward to the land of the rising Sun.
Greg Rudzinski
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