Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Avoiding Wx Problem
    From: UNK
    Date: 2000 Dec 15, 7:50 AM

    Robert Owens [mailto:tugly{at}neosoft.com] asked:
    
    > I have been studying for my Masters license and have come upon this
    problem:
    >
    > You are underway on a course of 050T at a speed of 12 knots. The eye of a
    > hurricane bears 120T, 110 miles from your position. The hurricane is
    moving
    > toward 285T at 25 knots. If you maneuver at 12 knots to avoid the
    hurricane,
    > what could be the maximum CPA.(Closest Point of Approach)1
    > The listed answer is 77 miles.
    >
    > I don't have a clue how to figure this one out. My Bowditch must be hiding
    > the obvious but I can't find it.
    > My first inclination is to draw the hurricane vector, then at the west end
    > of it draw a 12 mile arc, the draw a line from the east end of the
    hurricane
    > vector to the arc. that gives me about a 313T. Then I don't get anyway
    near
    > a 77 mile answer. More like 60 miles. Help.
    
    Construct a geographic plot with your initial position and the hurricane
    bearing 120dT at 110mi. Draw the hurricane's projected track of 285dT and
    extend it for 150mi (6 hours into the future). Since the test expects you
    to "maneuver at 12 knots to avoid the hurricane", construct a new course
    line from your initial position on a course of 015dT (perpendicular to
    the hurricane track) and extend it 72 miles (6 hours at 12kt).
    
    To find CPA distance:
    
     1. Lay your ruler along your new 015dT track and draw a line back along
        195dT until it crosses the hurricane track. This is the CPA.
    
     2. Measure the distance from the CPA back to the hurricane's initial
        position. Divide that distance (in miles) by 25 (hurricane's speed in
        knots) to get the time of CPA (hours in the future).
    
     3. Multiply that time by 12 (your speed in knots), giving the number of
        miles you will travel before CPA.
    
     4. Mark that distance on your 015dT track. The distance from there to
        the CPA point on the hurricane track is the CPA distance.
    
    I just tried this using the cheep protractor and compass at my desk and
    came pretty close to the book's answer of 77 miles.
    
     -- Peter
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site