NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Silicon Sea : Leg 69
From: Dan Hogan
Date: 2001 Apr 10, 21:37 EDT
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 Navigation-L List Owner http://www.wa6pby.com