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Subject: Re: Silicon Sea: Leg 71 (belatedly)
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Tue May 29 2001 - 13:38:33 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@XXX.XXX
Nav-L Web Page: http://www.wa6pby.com
Catalina 27 "GACHA"
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