# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Silicon Sea: Leg 80**

**From:**Bill Noyce

**Date:**2001 Oct 16, 5:36 AM

Better late than never, I hope. > The weather has been overcast for the past several days. Seas lumpy, and > wind variable. On 03/07/2001 at 01:37:00ZT and a distance of 754.0 Nmi on > a TC of 267.7d from our last position FIX at (03d 30.0' 097d 30.0'W) > 30/06/2001 {at} 11:53:00UT the navigator orders a turn to a TC of 307d. > > 1) What is the DR position at the time of the turn? > -- ------------------------------------------------ TC 267.7d = W 2.3d S Dist 754.0 nmi dLat = 30' S => DR Lat = 3d 0' N dep = 754 nmi => dLo = 753' W => DR Lon = 110d 3' W > At 09:27:06ZT that same morning we manage a Sun Lower Limb (Sun LL) sight > of: > Hs 42d 01.5' > > TC 307d, Speed 10.4 Kts. > > 2) What is the DR position at the time of the Sun sight? > What is the UT/GMT time of the sight? > -- ------------------------------------------------------ TC 307d = W 37d N time = 7h 50m 06s => dist = 81 nmi dLat = 48' N => DR Lat = 3d 48' N dep = 65 nmi => dLo = 65' W => DR Lon = 111d 8' W Zone is 7 hours west of Greenwich => UT = 16:27:06 Working the sight using the DR position as the Assumed position gives: GHA 178d 56.1' dec 22d 54.8' N Ho 42d 10.6' Hc 42d 12.2' Intercept: 1.6 nmi Away from 062.3d > At a DR position of (04d 10.1'N 111d 32.5'W) at 12:30:22ZT we manage > another Sun sight. > > Hs Sun LL: 71d 05.6' > > 3) What is 12:30:22ZT Sun sight called? > -- ------------------------------------ It's obviously close enough to local noon to give a LOP oriented mostly east/west, so could be called a "Latitude sight". A bit of work with the Almanac shows the sun's GHA is within a fraction of a minute of our estimated longitude, so this is definitely a "LAN sight" or a "Noon sight". As such, it gives Latitude directly with little calculation: Hs 71d 5.6' decl 22d 54.1' N -IC 2.5' -ZD 18d 44.5' -Dip 3.0' -------------- -Refr 0.3' Lat 4d 9.6' N +SD 15.7' =============== ---------- Ho 71d 15.5' ZD 18d 44.5' > 4) What is the Running FIX(RFIX) position? > -- --------------------------------------- For the RFIX, we must advance the earlier LOP to account for the motion from 9:27 to 12:30. We do this by advancing the Assumed Position from which the LOP is drawn. One way is by advancing the position by the given course, speed, and time. This gives a new Assumed Position of 4d 5' N, 11d 34' W. Since the earlier sight was worked with Apos = DR pos, we can simply take the new DR position as the place from which to draw the LOP. Which is better depends on why the new DR pos differs from the one I assumed for the earlier sight. Using 4d 5' N, 111d 34' W => RFIX = 4d 9.6' N, 111d 38.5' W Using 4d 10.1' N, 111d 32.5' W => RFIX = 4d 9.6' N, 111d 34' W ============================ For the remainder of the problem, I'll use the second solution (111d 34' W). > 5) What is the True Course(TC) and distance to the Hawaii landfall > point at (19d 30.0'N 154d 45.0'W)? > -- --------------------------------------------------------------- It's a long way! dLat = 15d 20.4, dLon = 43d 11' Even though it's not appropriate, I tried a Mid-Lat solution just to see what would happen, and got dist = 2710 nmi, TC = 289.7d. Using Great Circle, I get dist = 2687.4 nmi, TC = 296.7 (initial) ============================= The GC course is closer to the pole (expected), but I was surprised that the distances came out so close to equal. > The sky remains a heavy overcast. Winds are variable and indicate a slow > backing. We maintain at True Course of 289.9d. > > At the Running FIX position(RFIX) 03/07/2001 {at} 19:30:22UT, Current Drift 0.7 > Kts, Set 095d. Var 9dE, Dev 1.5dE. Speed 10.0 Kts. > > 6) What is the Compass Course(CC)/Course-to-Steer? > -- ----------------------------------------------- Not sure whether you're asking for TC 289.9d to be translated to a CCTS, or for my Hawaii course (TC 296.7d) to be translated to a CCTS. I did the latter, and came up with Steer 1.4d further West, and SOG = 9.3 kts TCTS = 295.3 => TVMDC => CCTS = 284.8d ============= > We travel for a distance of 646.6 Nmi on a TC of 289.9D. > > 7) What is the Dead Reckoning position at this point? > What is the Zone Time(ZT) and Zone Date(ZD) of the DR > position? > -- ------------------------------------------------------- Using the given distance and TC directly for DR: 289.9d = W 19.9d N dLat = 230' => DR Lat = 7d 59.6' N dep = 606 nmi => dLo = 604' => DR Lon = 120d 38' W ===================== I assumed the distance was distance through the water (measured by a log), not distance over the ground, so the time is found by dividing by 10.0 kts. 64.66 hrs = 2days 16h 40m + July 3 19:30:22 UT -------------------- We're now 8 hours west July 6 12:10:22 UT of Greenwich ==========> July 6 04:10:22 ZT ================== > 8) What is the UT/GMT time and date at the DR position? > -- ---------------------------------------------------- July 6 12:10:22 UT