NavList:

BTW, did you ever check my work?

gl

Greg R. wrote:

Assuming you're not being tongue-in-cheek with your solution (and being
at work I can't verify it right now), regardless of accuracy you
definitely get the Most Unique Solution award (plus an honorary
Navigator Who I'd Most Want To be Shipwrecked With plaque, with gold
clusters).  :-)

Heh... I almost wrote the exercise with all of the navigation books
being lost overboard too, and luckily the intrepid navigator had
memorized their entire contents - but figured that was a bit too much
of a stretch. Now I may have to re-consider that option...  ;-)

Assuming you're not being tongue-in-cheek with your solution (and being
at work I can't verify it right now), regardless of accuracy you
definitely get the Most Unique Solution award (plus an honorary
Navigator Who I'd Most Want To be Shipwrecked With plaque, with gold
clusters).  :-)

--
GregR



--- "Gary J. LaPook" <glapook@pacbell.net> wrote:

  

Being the conscientious navigator that I am, I followed my usual
practice of memorizing some data from the 2008 Nautical Almanac so
that
I would have it available for emergency use.

The first thing I memorized was the GHA of Aires at 0000 Z January 1,

2008 which is 100º 01.9' and also remembering that Aires advances
59.139' each day. With this information you can calculate GHA Aires
for
0000 Z on June 9, 2008 which is the 161st day of the year but is only

160 days from January 1st. So multiplying 59.139' times 160 days
gives
157º 42.2'  to which you add the starting value of 100º 01.9' to come
up
with the GHA Aires on June 9th at 0000 Z of  257º 44.1'. To this you
add
the change of GHA for the time since 0000 Z (3 hours 42 minutes 10
seconds for the Vega shot) by multiplying the time interval by the
rate
of change of 15.041º per hour making 55º 41.6' making the GHA Aires
at
the time of the Vega shot of 313 º 25.7'.

I also memorized the SHAs and the Declinations of ten of the
navigation
stars ( nobody could memorize all 57) which should be enough for
emergency use as tabulated for July 1st so that the values will be
reasonable for the whole year. Fortunately this included the three
stars
used in this exercise. So now adding the SHA of Vega, 80º  41' we end
up
with the GHA of Vega of 34º 06.7' and using the D.R. as the A.P. we
get
an LHA of 274º 48' and the declination of 38º 47' N. (rounded to the
whole minute)

Using these values on my Bygrave slide rule (see attached work sheet)

since I have no tables with me, I computed Hc of 23º 59'.

The Hs given was 24º 05.5' Computing the dip correction in my head of

4.5' (the square root of 20 must be between 4 and 5 ) and applying
the
refraction correction of minus 2 gives an Ho of 23º 59' giving and
intercept of zero and an azimuth of  58.1 º.  I long ago memorized
the
refraction table for altitudes above 10º in The Air Almanac and in
H.O
249, the cutoff values are 63-33-21-16-12-10º , zero above 63, 1
above
33, 2 above 21, 3 above 16, 4 above 12 and 5 above 10.

I used the same procedure for Spica and Pollux getting another zero
intercept for Pollux, Zn of 290.2º and a  4 NM away for Spica with a
Zn
of 171.7º.

Since I am on the road I do not have any of my plotting tools with me
so
I had to make do with what I found in my briefcase. I used my MB-2A
flight computer since it had an azimuth scale and I used a pad of
paper
with a right angle at the corner as my straight edge for plotting the

LOPs. I used a tape measure from IKEA to measure the length of the
intercept (see photo.)  I plotted the LOPs and found the fix by
bisecting the three angles giving a fix .4 NM west of the A.P. (D.R.)

and 2.8 NM north of it. (Plotting a fix as a distance from the A.P.
like
this is common in aerial practice and it is often done on an E-6B.)
Adding the 2.8 NM north to the D.R. latitude gives a fix latitude of
34º
16' North. To convert the .4 NM west  to a longitude you divide the
.4
NM by the cosine of the latitude, .82, to find the difference in
longitude of  .5' so the fix longitude is 119º 19.5' West (rounded to

either 119º 19' or 20'.)  ( I got the cosine of 34º by finding the
sine
of 56º on the MB-2A sine scale, used for wind correction
calculations.)

My fix might not be in agreement with others but I used a refraction
table tabulated in whole minutes, I only memorized the stars'
positions
to the nearest minute and I did not have any plotting tools to use
but
my position is certainly good enough for emergency navigation and
done
without an almanac, tables or electrons.

(I will have to send the images when Ii figure out how to make them
smaller.)

gl
1

m_burkes@msn.com wrote:

    

Captain Lecky would be proud of those dividers ha! Speaking of
interpolation I have found a neat way to get around that pesky DSD
      

and
    

interpolation tables by using the aviation E6B computer or the
equivalent nautical slide rule. Essentially the set up:d-value/60=d-
correction/declination minutes. Yes the calculator offers the proof.
Mike Burkes
On Jun 12, 11:44 pm, Anabasi...@aol.com wrote:


      

Thanks for the nice exercise Greg.  I literally had to dust off the
        

 ship's
    

Vol III of HO 229 and deflower a Plotting sheet 925 to work this
        

one  out.
    

Since I was bereft of electronic gadgets, I did this with a
        

plotting sheet,
    

2 triangles, a pair of dividers, 2 books, a pencil, and small piece
        

of scratch
    

paper (wouldn't have reams of paper in the Lifeboat).  I have
        

attached a
    

picture in to this message with the plot and the tools.

My Lat is a bit lower (plotting or math error?).  I used an assumed
        

 position
    

method and HO 229.  I had to assume we were drifting and no
        

current (didn't
    

advance or retard the lines).  I had not done a full HO 229  paper
        

reduction
    

of a star in many years, and I had to think a second to remember
        

how to use
    

the interpolation pages on the inside covers for the declination
        

interpolation.
    

I usually whip those off with the calculator.  Still,  I got
        

pretty close to
    

the computer solutions with Lat 34deg 11.9' N and  Longitude 119deg
        

16.0'W.
    

As to how you would get an Eastern sight on the west coast, you
        

would have  2
    

options in general.  The first would be a back sight.  This would
        

be
    

particularly difficult with a regular sextant at such a low
        

altitude.  The  other
    

option would be to use a bubble sight tube or other artificial
        

horizon.  If you
    

were across a bay, you could also use a dip short of  the horizon
        

table.
    

That's all I can think of at the moment.

Jeremy

**************Vote for your city's best dining and nightlife.
        

City's Best
    

2008.      (http://citysbest.aol.com?ncid=aolacg00050000000102)

gregExerPlot.jpg.JPG
182KViewDownload

GregExerTools.jpg.JPG
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