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On 03-17 @ 212624 hrs. Mr. Kenchington wrote that one cannot use sextant
horizontal angles to find distance off measurements or bearings.I must
differ with his opinion.Perhaps he did not understand  or misunderstood what
I was trying to explain.
The following is a simple explaination of the proceedure taken from the
books "Elements of Navigation" pgs. 140-143 by W.J. Henderson and "Coastal
Pilloting"pgs.89-93 by Commadore R.P. Ferchew.Each book has multiple
examples of the proceedures ranging from a simple 90* angle solution to
complex solutions for acute and obtuse angles.
Using the simple example of one of the objects @ 90* from the observer and
table 31,Bowditch and a calculator I did the exercize.I then used a UTM
projection and using 10 digit coordinates measured the distance between
electrical towers.I then calculated the distance off 2 of the towers and
fixxed a position.To keep the evolution simple I kept the 3 objects as close
to parrallel to my LOP as possible.Useing a handheld GPS I then went to the
calculated position fixxed from the projection.Using a sextant I then took
the Horizontal angles of the towers.I also took the bearings of the
towers.After the calculations were complete I used a laser rangfinder to
measure each distance.The delta between the chart measurements,sextant
measurements and the laser measurements were 5 ft.on the longest leg
distance and 2* T on the bearings.To me that proves one can get accurate
distance off and bearing measurements from Horizontal sextant angles.
The example:
                                                  C                    A
B
                                                   .                     .
.





                                                                          .
                                                                         O


Useing dividers measure the distance AB = 300yds. AC = 307 yds.
Useing the sextant find the angles AOB = 11* 32' 13". AOC = 11* 47' 33"
dist. off OB = 300yd./(sin 11*32' 13") = 1500 yds.
dist. off OC = 307 yd/(sin 11*47' 33") = 1502 yds.
Set dividers to 1500 yd. and swing an arc from B.Set the dividers to 1502
yd.and swing an arc from C.Where the 2 arcs intersect will be your
approximate position.Using parrallel rules find the bearings in * T of OB
and OC.Take the dividers and measure the line OA.This will be the distance
off A.One can calculate the dist. off A = 300 yd./(tan 11* 32' 13") = 1469.7
yds.

A = 307 yd./(tan 11* 47' 33") = 1470.5 yds.
There is also a nice technique for finding the ballpark distance off an
object over terrain useing a mil type lensatic compass I have used with good
results.If anyone is interested I will share it with you.

   

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