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Storm Avoidance: Course To Steer To Have Maximum CPA

You are underway on course 120°T and can make 12 knots. The eye of the hurricane bears 150°T at 120 miles. The hurricane is on course 295°T at 20 knots. What course should you steer at 12 knots to have the maximum CPA?

Given:  Own course = 120°T
              Own speed = 12 knots
     Hurricane bearing = 150°T
      Hurricane course = 295°T
       Hurricane speed = 20 knots

What is asked: Course to steer

Solution:
  1. We are going to divide own speed by the storm speed. 
  2. And then press inverse cosine. 
  3. Answer in #2 shall be added or subtracted the storm course. (Rule: + if storm bears quarter, - if storm bears bow)
So this is how to solve:  12 ÷ 20 = 0.6 inv cosine = 53° + 295° = 348°



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6 comments:

  1. MarCoMarch 17, 2014 at 9:17 AM

    do you have storm avoidance problems asking distance?

    ReplyDelete
    Replies
    1. NautaMarch 17, 2014 at 11:15 PM

      MarCo,

      Yes I have and I just posted it a couple of minutes ago.

      http://oic-nwreviewer.blogspot.com/#!/2014/03/storm-avoidance-maximum-distance.html



      Delete
    2. UnknownMay 4, 2014 at 4:24 PM

      I encountered a problem w/ a given: Own speed=10knots, Hurricane Speed= 19knots, huricane bearing= 285°T... but the correct ans.was 226, (could u pls explain this) thank u

      Delete
    3. NautaMay 5, 2014 at 5:09 AM

      Sir, your data is lacking. You don't give the ship's course. But anyway, I can guess where the storm is located in relation to your course because you have given me the answer which is 226° according to you.

      So this is it. 10 ÷ 19 = ans inv cosine = 58.24°. Since you said that the correct answer is 226°, so the storm is located to your bow; as 285° - 58.24 = 226.76°

      I hope this answer your question. If you have other questions, share it here so that readers to this blog may contribute something.

      Delete
  2. UnknownAugust 8, 2014 at 8:05 AM

    Could you please explain further about this, (Rule: + if storm bears quarter, - if storm bears bow) Thanks.

    ReplyDelete
    Replies
    1. NautaAugust 8, 2014 at 9:14 AM

      It simply means whether the storm is located to your front or to your back.

      Delete