NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Silicon Sea: Leg 70
From: Dan Hogan
Date: 2001 Apr 23, 11:51 AM
From: Dan Hogan
Date: 2001 Apr 23, 11:51 AM
On 23 Apr 2001, at 0:23, Yves Arrouye wrote: > > 1) What is the total distance in nautical miles to Cristobal? > > -- ---------------------------------------------------------- > > Using great circle sailings: > > Leg 1: 287.1d 84 Nm > Leg 2: 264.4d 519.9 Nm > Leg 3: 228d 712.3 Nm > > for a total of 1316.2 Nm. GC is OK for LONG distances but you need to watch the track for obstacles. Better methods are Rhmb-Line, Mercator Sailing, and Mid-Latitude Sailing. > > > 2) How many days (to the nearest tenth) is it to Cristobal? > > -- -------------------------------------------------------- > > At 7.5 knots, that's ~ 175 hours -> 7.3 days. OK > > 3) What is our Zone Time(ZT) ETA at the St. Lucia/St. Vincent > > Pass waypoint? > > -- ----------------------------------------------------------- > > Looking for sunrise in the Nautical Almanac, sunrise is 0532 at this > latitude. With current, our true course will be 287d at 8.7 knots. The sail > will take us 9:39 hours. The ETA is thus 1511 ZT. OK > > 4) What is the Compass Course/Course-to-Steer for the Pass? > > -- -------------------------------------------------------- > > 302, our TC being 287. OK. Thy calculating with a method other than GC. > > 5) What is our Departure point position to the nearest minute? > > -- ----------------------------------------------------------- > > 13d 25 N 61d 30 W Bang on. Using plotting sheet makes it VERY hard to calculate down to the nearest minute of arc. The answers for Silicon Sea are CALCLATED by a computer program, that's why they are to one decimal place. > > I used a plotting sheet printed from Ed Falk's site. I don't think I can be > precise to a minute of arc on these things printed as 8.2 x 8.2 inches. Can > you? > > > 6) What is the TC from our departure point to MOP1(12d 30.0'N 70d > > 00.0'W)? > > What is the distance? > > -- --------------------------------------------------------------- > > TC 264.7 Distance 500 Nm. OK. Try another method of calculation. > > > Var 13dW, Dev 1.5dE. Current Set 270d, Drift 0.7 Kts. > > > > 7) What is the Compass Course(CC)/Course-to-Steer for MOP1? > > -- -------------------------------------------------------- > > Assuming we still have a speed of 8.1 knots, CMG is 265 true at 8.8 knots. If > CMG is 265, CC is 276.5. OK > YA Dan Hogan WA6PBY Catalina 27 "GACHA" dhhogan@verimail.com Navigation-L List Owner http://www.wa6pby.com
