NavList:
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Re: Silicon Sea: Leg 72 -NEW
From: Dan Hogan
Date: 2001 May 26, 15:36 EDT
From: Dan Hogan
Date: 2001 May 26, 15:36 EDT
On 26 May 2001, at 13:43, Michael Wescott wrote: > > Sight Reduction and Revised > > Dead-Reckoning problem Leg 72 052301 Test your knowledge! > > ---------------------- ------ ------ -------------------- > > > > Our Last position FIX was (13d 00.0'N 61d 30.1'W) at 08:50:10UT on > > 30/05/2001. We are bound for a point on chart INT 401 marked as Aruba Gap > > (13d 50.0'N 70d 00.0'W). Aruba Gap provides a favorable westerly current of > > 1.5 Knts. > > > > We have had overcast skys and have missed some possible sights. The winds > > have been fluky and we have had to tack several times since our last FIX > > position. > > > > Tack 1: CC 333.0d - 04Hrs @XXX.XXX5 Kts - Var 12dW Dev 1dE > > Tack 2: CC 242.0d - 11Hrs @XXX.XXX5dE > > Tack 3: CC 262.0d - 08Hrs @XXX.XXX5dE > > Tack 4: CC 307.0d - 10Hrs @XXX.XXX0dE > > > > 1) What is the DR position at the end of the Tack 4? > > -- ------------------------------------------------- > TC Dist D.Lat dep > Tack 1: 319.0 30.0 22.6 -19.7 > Tack 2: 231.5 93.5 -58.2 -73.2 > Tack 3: 252.5 40.0 -12.0 -38.1 > Tack 4: 297.0 90.0 40.9 -80.2 > ============= > -6.7 -211.2 > D.Lo = -211.2/cos 13.4 = -216.8 = 3d 36.8' > > DR Position = 12d 53.3'N 65d 06.9W OK > > 2) What is the DR position local Zone Time(ZT) and Date? > > What is the DR position GMT/UT time and Date? > > -- ----------------------------------------------------- > 4 + 11 + 8 + 10 = 30hrs = 1d 6h Uhh..33 Hrs > > DR UT = 17:50:10 31/05/2001 > DR ZT = 13:50:10 31/05/2001 > > > 3) From the DR position, what is the TC to Aruba Gap > > (13d 50.0'N 70d 00.0'W)? > > -- ------------------------------------------------- > > D.Lat = 13d 50.0 - 12d 53.3 = 56.7 > D.Lo = -70d 00.0 - -65d 06.9 = 4d 53.1 = 293.1' > dep = 293.1 * cos 13d 20 = 285.2 > > TC = 270 + atan(56.7/285.2) = 281.2d OK > > Our speed is 8.5 Kts, Var 10dW Dev 1.0dE. Current Drift 0.7 Kts Set 265.0d > > > > 4) What is the Compass Course(CC)/Course-to-Steer for Aruba Gap > > from the DR position? > > -- ------------------------------------------------------------ > > CC = 281.2d + 10 - 1.0 = 290.2d OK > correction for current (by simple plot) adds a fraction more than > one degree: CC = 291.5 and gives a speed over ground of about 9.0 > > > The following morning the navigator see stars through breaks in the > > clouds. He takes the following sights. Same data as for Q3 & Q4. > > > > Body ZT Hs > > > > UNKNOWN 05:39:00 13d 53.6' (Bearing 349.7 M) > > Mars 05:39:11 18d 14.5' > > UNKNOWN 05:40:03 54d 58.9' (Bearing 327.3 M) > > Vega 05:41:06 40d 10.3' > > Venus 05:43:33 35d 25.8' > > > > 5) What is the FIX position? > > -- ------------------------- > > 9 knots @ 281 for 16 hrs gives AP of about 13d 20'N 67d 30W > > Plotting the sights gives us a crossings all in the vicinty of 67d 00'W > and 13d 30'N. A correction of 1.0' T gives a very small set of crossings > at > > 13d 30.5'N 66d 59.5'W OK > Was the IC really -1.5' rather than the -2.5' given? Yes. Thanks, I forgot to change it in the Master Problem NOTES. > > 6) What are the names of the two unknown bodies? > > -- --------------------------------------------- > > Unknown #1: > > 349.7 + 10 - 1 = 358.7d > > almost due north and altitude is about same as our latitude: > got to be Polaris Right > Unknown #2: > > 327.3 + 10 - 1 = 336.3 > > This is visually in the angle between Polaris to the north and Vega > to the northwest. GHA Aries is about 34d and Long is 67W so zenith > has SHA of about 33d. Looking at the starchart in the almanac, there > is only one navigational star between Vega and Polaris: Deneb Right > > 7) What is the TC and Distance to the Aruba Gap (13d 50.0'N 70d 00.0'W) > > waypoint from our FIX? > > -- --------------------------------------------------------------------- > > dLat = 13d50.0' - 13d30.5' = 19.5' > dLo = 70d00.0 - 66d59.5' = 180.5' > dep = 180.5*cos 13d40' = 175.4 > > TC = 270 + atan(19.5/175.4) = 276.3 > Dist = sqrt(19.5^2 + 175.4^2) = 176.5 OK Dan Hogan WA6PBY Catalina 27 "GACHA" dhhogan@XXX.XXX Navigation-L List Owner http://www.wa6pby.com