# NavList:

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

**Re: Silicon Sea: Leg 71 (belatedly)**

**From:**Dan Hogan

**Date:**2001 May 29, 13:38 EDT

On 29 May 2001, at 9:45, Noyce, Bill wrote: > > 1) At the log reading of 89.6Nmi, what is the DR position? > > -- ------------------------------------------------------- > Mid-Latitude Sailing using L=13d 20' > TC = 263.7 dLat = 9.8' S dep = 89 nm W DLon = 91.5' W > DR position = 13d 15.8' N 63d 1.6' W OK > > 2) At the DR position what is the celestial phenomena that is > starting > > at this DR Zone Time(ZT)? > > -- > ------------------------------------------------------------------- > > 18:27:00 + 10.3 hrs = 04:45 ZT 30 May > At this time and position, I find the sun's altitude is -13d 58' > -- still 2 degrees short of the start of Nautical Twilight. > But if we're actually 1.5 degrees east of here, that would > explain most of the difference. Ok--it's MNT > > 3) What is the FIX position? > > -- ------------------------- > > Using the above DR position, > > Body Fomalhaut Polaris Deneb Vega > GHA 36d 3.0' 342d 53.1' 70d 20.8' 102d 8.4' > Decl S 29d 36.9' N 89d 16.1' N 45d 16.8' N 38d 47.0' > Hc 39d 50.8' 13d 23.4' 57d 23.5' 47d 5.2' > Az 149.1d 0.7d 350.4d 313.9d > Int 58.2' T 14.8' A 32.4 A 75.0' A Hmmm...something very wrong with the Polaris Dec. CAN'T be that high. Polaris gives your latitude with its LOP. > Pretty long intercepts, and a poor cut. I used Ageton's > method, and for Polaris found why it's not recommended for > LHA near 90 degrees with high declination -- you end up > trying to find an angle whose sine is about 1.0, and since > the function doesn't vary rapidly there, the angle isn't > established with any precision. So instead of using > sin K = sin decl / cos R > I tried > cos T * sin R cos T * cos d > cos K = cot T * tan R = ------------- = ------------- > sin T * cos R cos R > Is this Sadler's modification to Ageton's method? > > Anyway, I tried again with an AP of 13d 0' N 61d 30' W > and got intercepts of > Fomalhaut: 0.3' A > Deneb: 0.3' A > Mars: 4.6' A > Venus: 0.1' A > Vega: 0.1' A > and except for Mars, it looks like we're there. I wonder if > I made an obvious mistake here: > Mars > GHA 114d 23.9' > decl S 25d 47.5' > K S 38d 42.0' > Hc 25d 33.1' > Az 232.8d ??? FIX > > 4) What is the TC and Dist from our FIX to the Aruba Gap > > (13d 50.0'N 70d 00.0'W) > > -- ------------------------------------------------------ > > Mid-Latitude (using 13d 25') > dLat = 50' N Dlon = 510' W log(dep) = 1.69897 > TC = 275.7d Dist = 499 nm Hmm, TC is off. Check the FIX. > > 5) What is the Compass Course(CC)/Course-to-Steer for Aruba Gap? > > -- ------------------------------------------------------------- > > TVMDC, West is Best, add 11d: 286.7d OK > > 7) What is the anticipated Speed Made Good(SMG) to Aruba Gap? > > -- ---------------------------------------------------------- > Current essentially right on our tail, 9.3+0.8 = 10.1 kts OK > > 6) What is the time enroute to Aruba Gap? > > -- -------------------------------------- OK > 2 days + 1h 24m Dan Hogan WA6PBY dhhogan{at}XXX.XXX Nav-L Web Page: http://www.wa6pby.com Catalina 27 "GACHA"