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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Re : Silicon Sea: Leg 70**

**From:**Sam Chan

**Date:**2001 Apr 23, 1:25 PM

Dan, I did not use a program for all the calculations except for the course and distance for the Mid-latitude sailing which I used the Starpilot from Starpath. The sailings, both traditional Mercator sailing and the modification to it using the Latitude Parts table were done by hand with the help of a Casio fx-300W (see below for more about this calculator). I have implemented the Mercator sailing using Meridional parts and Latitude Parts using the Quattro Pro speadsheet to evaluate the differences between the two methods. The determination of CTS and visual fix was done on a plotting sheet. Now about the fx-300W. I was shopping around for a calculator to use for sight reduction by hand without the aid of a programmable calculator. I have traditionally been an HP fan my self. However, the Casio fx-300W caught my eyes due to its implementation of the sexagesimal calculation. Angles and time can be entered in degees(hours), minutes, and tenth of minutes. Values can be computed in terms of hours, minutes, and seconds, and can be easily converted back and forth between decimal and sexagesimal format. The other feature about the fx-300W is that it has a two line display. You can see what you entered before you hit the equal key. It also has seven memory registers for storing repeated data and computed values. It has a lot more capabilities like statistical and regression analysis. The calculator only costs about $15 so I will not feel that bad if I loose one. Sam ----- Original Message ----- From "Dan Hogan"To: Sent: Monday, April 23, 2001 10:51 AM Subject: Re : Silicon Sea: Leg 70 > 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 {at}7.5Kts 163h 21.6m 162h 20.8m 163h 16.8m > > > > 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{at}verionmail.com >