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Re: Silicon Sea : Leg 69
From: Dan Hogan
Date: 2001 Apr 10, 21:37 EDT

```On 10 Apr 2001, at 16:25, Sam Chan wrote:
[Snip previous]
>
> Using a new course of 298T, I get the following results using a method
> that account for the ellipsoid eccentricity: DR = 13d 21.8N, 59d 44.3W. I
> used a table of Latitude Parts to calculate the difference in latitude
> parts in place of the difference in latitude. The table is similar to the
> table of Meridional parts. The table of Latitude parts was generated using
> the eccentricity of WGS84. What method is used in your program?
Currently set to Clarke of 1866
> >
> > In setting up the problems I work some backwards from the answer I want.
> >
> > > For question 7, I got an answer of CTS 338 C with a SMG of 10.9 Kt.
> > > The Star Pilot gave an answer of CTS 324.4T and SMG of 10.9. Applying
> > > the Var
> > > 15dW (add), and a Dev 1dE (subtract), I arrive at a CTS of 338.4 C. I
> > > double checked the Star Pilot with a plot on the Mo Board and also
> arrived at a CTS of 324T.
> >
> > Using several checks I keep getting 332.0d. But the DR being off would
> > account for the difference.
> >
>  Question 7 is a problem in current sailing and I don't see how the DR
> position would affect it other than the magnetic variation which was given
> in the problem. Using the Mo Board, I constructed the CMG at 318T. I then
> construct the current set and drift at 270T /1.5 kt. Both vectors starts
> at the center of the board. I then took a divider set at 10 kts, the boat
> speed, place one end at the head of the current vector and the other end
> on the CMG line. The line connecting the two points was my CTS. This is
> how I arrived at a CTS of 324T. The correction to compass course is the
> standard TVMDC AW. See any problems?
OK, I see the problem. It's a difference in naming the result. I should
have asked for TC Made Good or else eliminated the current effect. So
either answer is acceptable. Sure stirs up activity.
VELOCITY TRIANGLE NAVEX SYSTEMS (c)
Variation 15.0d W         Deviation  1.0d E
------V1------            ------V2------            ------V3------
Speed     10.0            Drift      1.5            SpMdGd    11.1
TrueCrse 318.0d           Set      270.0d           TCMdGd   312.2d
CompCrse 332.0d                                     CCMdGd   326.2d
Dan Hogan WA6PBY
Catalina 27 "GACHA"
dhhogan@XXX.XXX
http://www.wa6pby.com
```
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