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Re: Silicon Sea Leg 72
From: Dan Hogan
Date: 2001 May 29, 13:38 EDT
From: Dan Hogan
Date: 2001 May 29, 13:38 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"