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> > > 4)  What is the Compass Course(CC)/Course-to-Steer for Aruba Gap
> > >     from the DR position?
> > > --  ------------------------------------------------------------
> >
> > Using Law of Sines, I find I need to adjust my course North
> > about 1.5 degrees.
> >   CC = 283.4 + 1.5 + 9 = 293.9d
>
> Mmmm..Barely OK. Try a current vector diagram.
I drew a diagram to get the orientation of the pieces right, but I
have a hard time measuring the resulting course adjustment, because
it's so small.  Thus the attempt at a 'digital' method.
TC=283.4, Set=265.0, angle between = 18.4 degrees
  sin 18.4 / speed = sin adj / drift
  sin 18.4 / 8.5 = sin adj / 0.7
I did this with log tables before; doing it on the computer now
says adj = 1.490 degrees.  The diagram indicates it needs to be
added to the course.  Is there something inherently wrong with
this approach, or have I made a slip somewhere?
> >
> > Mid-latitude using 13d 42'
> > dLat = 15' N  dLon = 183d W  dep = 177.8 W
> > TC = 274.6d  dist = 178.3 nm
>
> OK. Be aware that above 500 miles at 90d/270d Mid-Latitude can give an
error.
> Above 1200 mils it gets unreliable.
I saw a discussion initiated by Sam Chan about Mercator sailing
near 90 or 270, where the problem arises from rounding the course
before using dLat/cos(C) to compute the total distance.  Is this
a similar problem?  In Mid-Latitude sailing, where we already
have dLat and departure, the total distance can be computed either
as dLat/cos(C) or as departure/sin(C), so we don't have to divide
by a tiny rounded number.
Or are you talking about the error in distance that arises from
assuming a spherical earth?  What method would be
better? I assumed we weren't planning to sail a great-circle
course here.

   

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