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    Re: Closest point of approach.
    From: Gary LaPook
    Date: 2011 Dec 27, 01:11 -0800
    Sure, it's easy. I have attached several photos of a sample plot to show how the calculation proceeds.
    At 0120 the vessel bears 060° relative, distance 4.0 NM.
    At 0126 the vessel now bears 043° R, 2.2 NM.
    The difference in bearings is 017°.
    With this information we use the law of cosines to find the length of the third side which is 2.0022 NM.
    With the lengths of all three sides we use the law of sines to find the angle between the relative bearing to the second position and the direction of relative movement which is 35.7°.
    At the point of closest approach the angle between the realative bearing and the direction of relative movement is 90° the sine of which is 1.
    Now using the law of sines again we compute the distance at the point of closest approach which is 1.28 NM.
    Using the law on sines again we compute the distance the other vessel moves from the second position to the point of closest approach which is 1.78 NM.
    Next we divide this distance by the distance traveled between the first two positions and then multiply by the time between the first two positions to find the time to the point of closest approach which is 5 minutes and 21 seconds.

    gl

    --- On Mon, 12/26/11, Amrin Shahziya <ammushaz@gmail.com> wrote:

    From: Amrin Shahziya <ammushaz@gmail.com>
    Subject: [NavList] Re: Closest point of approach.
    To: NavList@fer3.com
    Date: Monday, December 26, 2011, 10:45 PM

    Instead of plotting is there any other way to calculate the closest point of approach using speeds and courses?

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