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Hi Peter,

I used a 30+ year old NC-2 hardwired navigation calculator which was jointly
developed by Nautech Maritime Corporation, of Chicago, IL and Tamaya & Co,
Tokyo, Japan, and your arguments. The solution is a zero intercept, as you
said.

BTW, I haven't used it in years, but it still does what it was designed to
do.

Joel Jacobs


----- Original Message -----
From: "Peter Fogg" 
To: 
Sent: Friday, January 30, 2004 11:10 AM
Subject: Re: Silicon Sea Leg 88 questions


> Hi again Renee
>
> Recently I posted to the Nav List, in answer to your query:
> > >  Peter -- I disagree on the solution to part 5
> > >   You can't set
> > > the Intercept to 0.
> my response:
> > My calculated intercept via one method, capable of resolving this to the
> > nearest minute of arc, was zero.
> > I've now checked this with another method (don't be lazy myself!) and
> > agree with your answer.
>
> I've had another look at this Question 5. The time given is within a
couple
> of seconds of local noon, so treating it as a meridian passage of the sun
> gives a latitude of N39d 46' which is the DR latitude, so via a sight
> reduction method a zero intercept, as my original answer. So I've redone
the
> sight reduction two ways and confirmed the zero intercept, meaning the
> computed altitude and the (corrected) observed altitude are both 54d 58'
(to
> the nearest minute of arc).
> What intrigues me now is how I got an identical answer to yours, quickly
> using my nav. calculator. I can't get it again!
>
> Here are my steps for a noon sight:
>
> sextant altitude   54 48.1
> dip                          -2.9
> index error              -2.5
> apparent alt        54 42.7
> alt corr                  +15
> observed alt        54 58 (rounded to nearest minute of arc)
>
>                            89 60 (another way of expressing 90d)
>                          -54 58
>  zenith distance    35 02
> declination        + 04 44
> =  latitude            39 46
>
> Could you check your calculations for Q5, perhaps also work the problem as
a
>  noon sun sight, and let me know the results? I'm still not sure I
> haven't made a mistake somewhere.
>
> It would be good to check our answers against the official ones, but
despite
> a posting by Dan Hogan (the author and webmaster) that "ssea.zip has been
> upgrades to include Leg 83" I can't find a link on http://www.wa6pby.com/
> that leads to the Silicon Sea archive. In any case, it apparently won't
> include Leg 88. I've had a look for the answers on the Nav List archives
and
> can't find them there either. Were they ever posted?
>
> Some more comments on your answers follow:
>
> > > 1) DR #1 39d39.4' N 154d 42.4'W
>
> This is identical (to the nearest tenth of a minute of arc) to the most
> accurate method I have, using both meridional parts and distances. My
answer
> was rounded to the nearest minutes of arc.
>
> > > 3)
> > >   78.5d, 1652 nmi via the Rhumb Line
> > >   67d, 1639 nmi via the Great Circle. (67d for first leg.)
>
> By comparison, my answer to nearest tenth of degree or nautical mile
> 078.8d for 1652.2nm rhumb line
> 066.6d (initial) for 1634.1nm great circle
> is slightly different, implying that you used a different method for these
> calculations?
>
> I note you are using mainly electronic solutions. You might like to
consider
> having, at least as a back-up that needs no batteries or internet
> connection, a manual alternative that only requires pencil and paper. Its
> good to be able to check results from any method with another independant
> method.
> If you're interested I have a suggestion as to a reasonably simple paper
> alternative (including "celestial data") to electronic calculations.
>
> In any case, for "a self-taught beginner" you're not doing too badly.
>
> Peter Fogg

   

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