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    Re: Rusty!!!!
    From: Eric Haberfellner
    Date: 2001 Dec 03, 7:47 PM

    I am also confused about what method to use for solving question 1. Here is
    a copy of a note that I sent to Dan asking for help. Perhaps some of the
    other listers can give me a hand.
    
    -----Original Message-----
    From  Eric Haberfellner [mailto:ehaberfe{at}rogers.com]
    Sent: Sunday, December 02, 2001 10:15 PM
    To: dhhogan{at}VERIOMAIL.COM
    Subject: RE: Silicon Sea: Leg 82
    
    OK, I am already having a problem on part 1 of this problem. The initial
    course that I calculate for the great cricle course is 282.7466d, not the
    given answer. How I got there is this.
    
    The formula for calculating the great circle initial course angle given in
    Bowditch is:
    
    Where L1 is lat. of departure
    L2 is lat. of dest.
    DLo is difference in long.
    
    C = arctan ( sin DLo / ( (cos L1 * tan L2)-(sin L1 * cos DLo) )
    
    So we calculate:
    
    DLo = -22.7466d (decimal degrees)
    L1 = 11.4967d
    L2 = 19.5000d
    
    We plug these valuse into the equation and we get
    
    True Course = -66.7735 = 293.2265d.
    
    Now we uncorrect for deviation and variation. Timid Vrigins Make Dull
    Companions and Uncorrecting east is least, so:
    
    Magnetic course = True course - 10.0d E. Var. - 1.0d E. Dev. = 282.2265d.
    
    Now for the current, The Annapolis Book of Seamanship gives the formula for
    correcting magnetic course for a current as:
    
    Where RL is magnetic Rhumb-line course = 282.2265
    drift is speed of current in knots = .7 knots
    set is direction of current in magnetic degrees = 285d - 10.0d E. var. =
    275d M
    boatspeed is in knots = 9.7 knots
    
    Mag course = RL - arcsin ((drift * sin(set - RL))/boatspeed)
    
    Plugging in the values we get magnetic course 282.7466d.
    
    Where the heck did I go wrong??
    

       
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