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Subject: Re: Silicon Sea Leg 72
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Tue May 29 2001 - 13:38:33 EDT
On 29 May 2001, at 10:27, Noyce, Bill wrote:
> > 1) What is the DR position at the end of the Tack 4?
> > -- -------------------------------------------------
>
> Tack 1
> TC 322.0d 231.5d 252.5d 297.0d
> dist 30.0 nm 93.5 nm 40.0 nm 90.0 nm
> dLat N 23.6' S 58.2' S 12.0' N 40.2'
> Lat N 13d 23.7' N 12d 25.5' N 12d 13.5' N 12d 53.7'
> dep W 18.5 nm W 73.2 nm W 38.1 nm W 80.2 nm
> dLon W 19.0' W 75.1' W 39.2' W 82.3'
> Lon W 61d 49.0' W 63d 4.1' W 63d 43.3' W 65d 5.6'
>
> DR = 12d 53.7 N 65d 5.6' W
OK
> > 2) What is the DR position local Zone Time(ZT) and Date?
> > What is the DR position GMT/UT time and Date?
> > -- -----------------------------------------------------
>
> 33 hrs = 1 day 9 hrs:
> UT 31 May 17:50:10
> ZT 31 May 13:50:10
OK
> > 3) From the DR position, what is the TC to Aruba Gap
> > (13d 50.0'N 70d 00.0'W)?
> > -- -------------------------------------------------
>
> TC = 283.4d dist = 291.7 nm
Mmmm..OK
> > 4) What is the Compass Course(CC)/Course-to-Steer for Aruba Gap
> > from the DR position?
> > -- ------------------------------------------------------------
>
> Is current set given in True, Magnetic, or Compass direction?
> Not that it makes much difference here. I assumed True.
> Using Law of Sines, I find I need to adjust my course North
> about 1.5 degrees.
> CC = 283.4 + 1.5 + 9 = 293.9d
Current, wind, etc. are ALWAYS in TRUE.
Mmmm..Barely OK. Try a current vector diagram.
> > 5) What is the FIX position?
> > -- -------------------------
>
> Roughly estimating progress westward for 16 hrs, I picked
> AP = 13d 20' N 67d 30' W
> It wasn't until checking my work that I noticed this puts
> us right on the border of a time zone, but if I get the
> conversion ZT->UT wrong the 15-degree error in position
> will be obvious.
>
> Body Mars Vega Venus
> GHA 128d 45.8' 115d 58.2' 11d 32.5'
> Decl S 25d 54.5' N 38d 47.0' N 7d 49.7'
> Hc 18d 41.3' 40d 19.9' 34d 47.7'
> Az 236.4d 310.0d 89.6d
> Int 35.3' A 16.3' A 31.2' T
>
> These give a position at about 13d 35' N 66d 57' W.
> This is about 30 miles east of my rough estimate.
> Perhaps we were running only about 12 hours instead
> of 16, due to UT/ZT confusion?
The time zones are 7.5 degrees either side of the principle zone.
Zone Description(ZD) = Lon / 15
If it's 4.4 still in previous zone, if its 4.5 you are in the next zone.
>
> > 6) What are the names of the two unknown bodies?
> > -- ---------------------------------------------
>
> Running a signt reduction but exchanging Ho<->decl
> and LHA<->Bearing, I get
>
> Compass bearing 349.7d 327.3
> True bearing 340.7d 318.3
> computed decl N 71d 17.2' N 29d 51.2'
> computed LHA 87d 48.0' 33d 44.7'
> GHA 154d 45.0' 100d 41.7'
> SHA 119d 23.2' 65d 44.7'
>
> None of the planets are near the resulting position, and
> none of the 58 'standard' stars are very near. I concluded
> that the northern one was in the bowl of the Little Dipper,
> but it's not Kochab; the second looked like it might be the
> head of the Swan, opposite Deneb in Cygnus. Now that I see
> the second correction, perhaps I'll go back and redo them...
I screwed this up as much as any one. The simplest method is to use the
Almanac and find a body with a close GHA and dec. Other wise use yout SR
Table and solve for:
In place of dec use Ho
In place of LHA use Obs Azimuth
In place of Hc find Dec
In place of Z find LHA
> > 7) What is the TC and Distance to the Aruba Gap (13d 50.0'N 70d
> 00.0'W)
> > waypoint from our FIX?
> > --
> ---------------------------------------------------------------------
>
> Mid-latitude using 13d 42'
> dLat = 15' N dLon = 183d W dep = 177.8 W
> TC = 274.6d dist = 178.3 nm
OK. Be aware that above 500 miles at 90d/270d Mid-Latitude can give an error.
Above 1200 mils it gets unreliable. When I used Mid-Latitude (Hawaii to Long
Beah, CA)I broke the passage into 600 Nmi legs, it fits the Pilot Charts.
Dan Hogan WA6PBY
dhhogan@XXX.XXX
Nav-L Web Page: http://www.wa6pby.com
Catalina 27 "GACHA"
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