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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.
           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"
    Navigation-L List Owner

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