NavList:

   

Reply

Sam:
Sorry for the delay on my response. I had to unscramble the layout. When
layouts exceed the width of the screen adding the reply symbol messes it up.
On 22 Apr 2001, at 13:54, Sam Chan wrote:
> Here are some of the numbers I came up with:
>
> 1. Distance to Cristobal. I computed the distance between the various way
> points using three methods: (1) traditional Mercator sailing using tables of
> Maridional Parts, (2) Mercator sailing using a table of Latitude Parts which
> accounts for the eccentricity of the earth when calculating the meridian
> distance from initial to final latitude, and (3) the Starpath Starpilot which
> uses mid-latitude sailing. Only the distance is different between these three
> methods. The course are identical.
>
> Way Point                          D by (1)         D by (2)        D by (3)
> Course (T) Bridgetown St Lucia/St Vincent Pass          84.8              84.2
>            84.5 286.8 MOP1                                  522.0
> 518.8          523.2 263.4 Cristobal                               618.4
>      614.6 616.9                 252.4 Total
> 1225.2          1217.6        1224.6
OK. Distances will vary depending on what method is used for calculation.
Occasionally TC will vary +/_ a degree depending on the method and direction
> Enroute time @XXX.XXX8m
>
> 2. Days to Cristobal. To the nearest tenth, 6.8 days.
OK
> 3. ETA in Zone time at the St. Lucia/ St. Vincent Pass waypoint.
>
> Sunrise on 29/5/2001 at Bridgetown 13d 05.5'N, 59d 47.4'W is 0532Q. The
> central meridian for the time zone is 60d W and the 12.6' of longitude east of
> the central meridian did not affect the SR time significantly. So departure is
> at 0532Q.
>
> There are two ways to get at the ETA. The course to the waypoint is 286.8. If
> we go with the boat speed of 8.1 kts, and the distance is 84.8nm, the enroute
> time is 10h 28m and the ETA is 1600Q. However, given the current set of 270,
> drift of 0.7 Kts, and steering 288 T, the resulting SOA is 8.8 Kts on a Track
> of 286.8 T. The enroute time is then 9h 38m with an ETA of 1510Q.
OK. Out of curiosity, what program are you using for your calculations?
>
> 4. Compass course/Course-to-steer (CTS). Setting a course so that our Track is
> 286.8 T, the CTS is 303 C. When the current is not accounted for, the CTS is
> 302 C. This is to be expected since the current set is so close to the desired
> track.
OK.
>
> 5. Departure point position to nearest minute.
>
> St. Lucia at 292.2 d C is 279.2 T
> St. Vincent at 129.7d C is 116.7 T
> By plotting out the fix on a plotting sheet, the fix is at 13d 25.5' N, 61d
> 29.8' W.
OK.
> 6. TC and distance to MOP1 from departure point from 5.
>
> The course is 263.7 T. The distance is 502.8 NM using method 2.
OK.
> 7. CC/CTS for MOP1.
>
> The set of the current is so close to the desired track that it has very
> little impact on the CTS. So CTS is 274.5 C.
OK.
> Sam Chan
Dan Hogan
dhhogan@XXX.XXX

   

Reply