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    Re: Silicon Sea: Leg 70
    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{at}verimail.com
    Navigation-L List Owner
    http://www.wa6pby.com
    

       
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