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Doug,

I don't know if this is germane to your approach, but if you preset your
sextant altitude, and time a rising body to the east, and then time how long
it takes to achieve the same exact altitude to the west, wouldn't averaging
the time, and plotting, result in your longitude. And hence derive local
time without the use of a chronometer. Also, if at morning or evening
twilight, you set your course to true N or S, and shoot a body directly
perpendicular to either beam, the lop obtained should be your lon.

Joel Jacobs

----- Original Message -----
From: "Royer, Doug" 
To: 
Sent: Wednesday, January 21, 2004 3:39 PM
Subject: Timed Noon sights for position


> A while ago I posted a technique to use the Noon sight to obtain a
> "passable" estimate of both Lat. and Long.Some fellow list members replied
> in horror and disbelief that I would post this.Only 1 other listmember
> stated that a well managed Noon sight could be used to obtain more than an
> estimated Lat.
> While at sea for the last weeks I had time to attempt to take actual
sights
> and reductions of the Noon sights and present the data from these sights
to
> the list.We proceeded from Pt. Furmin T.S.S. to an area in the Pacific to
> drop bouys,take data and retreive the bouys.
> This is mainly a mechanical proceedure and with practice is not that
> diffacult to acheive.Care must be taken in the timeing of the sight or the
> errors can give results that are grossly differant from the actual
position.
> There are 2 keys in the proceedure to accomplish this.Being ready at the
> calculated time to take and record the cut and correct calculation of the
> 1st and 2nd approximation of the EP.The takeing of the cut at the correct
> time is all mechanical and the more one does it the better one becomes at
> it.The accuracy of the calculated EPs to the actual positions is largely
> reliant on how close one keeps the vessel to the trackline.On the bigger
> vessels the helmsman has standing orders to head the vessel in a momentary
> direction(overriding the auto-steering)to keep the vessel within a certain
> distance of the trackline.This assures the Ep and position of the vessel
are
> close.
> The Lat. and Long. were reduced.Plotting sheets were used and the ship's
GPS
> position was used only to compare the closeness or distance of the reduced
> positions.
> Constants for all sights : Ie=-0.1'.ht.=28 ft.Sun's L.L. used on all
> sights.EP used as the AP for the sights
> Depart 33* 20.0'N, 118*05.0"W, 0737, 1-15-04.C=209*T, s=15 kt
> 1st approx. EP 1209 LMT M.P.1-15-04 32*20'30"N,118*44'27"W
> 1209 lon.=118*44'27"W
> n.l. GHA=117*40'12" at 200000 GMT
> d GHA= 1*4'15"
> d T =     4'17"
> cor GMT=200417
> zd = + 8 rev.
> zt LAN=120417
> 2nd approx. EP 1204zt  32*21'36"N,118*43'45"W
> c.l. lon. = 120* W
> 1204 lon.=118*43'45"W
> d * = 1*16'15"
> d T = - 5'5"
> LMT 120919
> zt LAN=120414 I didn't get the sight taken on time.12 sec. late
> LAN temp.=53* F,29.80' Hg,hs =36*21.4',Ho=36*31.3',dec
> =21*07.9'S,GHA=118*46'42"
> 120426 noon pos.=32*20'48"N,118*46'42"W
> 1204 EP=32*21'36"N,118*43'45"W
> 1205 gps= 32*19'55"N,118*43'47"W
> 1-16-04 0325 arrive in test area.Propulsion cut,deploy bouys.collect
> data.Ride shotgun on bouys and show lights for RAM
> 0325 gps= 28*45'6"N,121*04'18"W.    Check gps pos. at 0625=
> 28*42'54"N,121*09'39"W. drift=240*T,s=1.77 kt.
> 1st approx. 1210 LMT EP= 28*37'45"N,121*19'27"W
> LMT lon.= 121*19'27"W
> n.l. GHA= 117*34'54" at 200000 GMT
> d GHA= 3*44'33"
> d T= 14'58"cor GMT= 201458
> zd=  +8 rev.
> zt LAN= 121458
> 2nd approx. EP= 28*37'44"N,121*19'27"W
> c.l.lon.= 120*W
> 1215 lon.= 121*19'27"W
> d *=1*19'27"
> d T= + 5'18"
> LMT= 120940
> zt LAN= 121458    I was late again on the sight
> LAN temp.=51* F,29.78'Hg,hs=
> 40*15.4',Ho=40*25.5',dec.=20*56.6'S,GHA=121*19'24"
> 121459 noon pos.= 28*37'54"N,121*19'24"W
> 1215 EP= 28*37'44"N,121*19'27"W
> 1215 gps= 28*37'49"N,121*19'29"W
> 1-16-04 1438 shot a sun line to combine with noon pos. Clouds starting to
> cover sky,winds increasing temp.=48*F,29.78'Hg
> 1438 EP= 28*35'47"N,121*23'36"W
> dec= 20*55.4'S
> hs=29*30.1'
> Ho= 29*39.6'
> Hc=29*39.4'
> a= 0.2m T
> 143812 r-fix pos= 28*35'48"N,121*24.0'W
> 1438 gps= 28*36'00"N,121*24'07"W
> For the next 37 hrs. no sights could be attempted due to cloud
> cover.Departed the area 1-19-04 at 1733.I took 1 more noon sight on the
20th
> on a north heading giveing similar results between the gps and reduced
> positions.Even the 1-15-04 pos when I missed LAN by 12 sec. was less than
5
> n.m. from the gps pos.The 16th's LAN  and r-fix pos. had less than 1 n.m.
> seperation from the gps pos.The closest land from this area is 133 n.m.
> So,I ask,what is so very wrong about showing someone this method?What do
you
> feel is so difficult in timeing a sight?Even if one's timeing of the noon
> sight is off by many secounds one can still get a "passable" fix.If the
> conditions after the 16th's noon pos were such that you couldn't get any
> LOPs for days after and didn't have gps,software for a trackline or a
> reliable auto-pilot it gives one a better idea of where one was then just
a
> Lat estimation at LAN.Would I depend on this method solely for position
> finding approaching land or in congested areas?No.But then again,in todays
> world,one doesn't have to depend on CN position finding at all.It's just
> another tool to use when needed.There is a seperation from strict theory
and
> practical applications and methods used in real navigation.
> This subject won't die and be buried by anyone.
> Mr. Reed,I read your post with great interest this morning concerning star
> to star sights.The proceedure you talk about useing I've read in a few of
> the older navigation books but never really gave it more thought.Maybe
I'll
> try it in the future for something to do.When is part 2 going to be
posted?

   

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