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Old 03-02-2010, 12:02   #1
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Help on Coast Guard Captain's Exam

In preparation for the Captains license exam, I've run across a couple of question types in the Navigation General section that I am having difficulty with and I would appreciate some advice.

These are multiple choice questions, and I am looking for a rule of thumb, a formula or something. My approach so far has been to drag out a chart and plot all the parameters give and see if I can fill in the holes. But I find it hard to believe the exam requires this. I would really like to understand how to do this relatively quickly in real life too!

Type 1 - The question provides course and speed of another vessel and asks you to solve for either your course to intercept, or the time at which you will intercept.

Example: You are enroute to assist Vessel A, which is on a course of 063T at 5kts, and bears 136T at 78 miles from your position. What is the course to steer to intercept, assuming you make 13kts? Another variation asks how many hours until you intercept.

Answers: 340; 295; 158; 114

Type II - These questions relate to avoiding something - usually a hurricane (which seems like a real good idea). The skill is computation of the maximum closest point of approach (CPA). In other words, what is the course that will minimize contact with the hurricane.

Example: You are underway on a course of 050T and your maximum speed is 11kts. The eye of a hurricane bears 070T, 80 miles from your position. The hurricaneis moving generally towards 270T at 19kts. If you maneuver at 11kts to avoid the hurricane, what could be the maximum CPA? Note this doesn't ask for the course, but I guess you've already determined that in order to choose the correct answer.

Answers: 84mi; 79mi; 74mi; 66mi

Thanks for your help!
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Old 03-02-2010, 12:32   #2
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You're asking maneuvering board questions. They take seconds for an experienced navigator to plot. No shortcut needed--just practice moboard plotting.

Brett
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Old 03-02-2010, 12:33   #3
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Use plotting paper and a protractor and the answers are easily obtained.

But, as an Ocean Master with many years of steaming around the world under my belt, I find these type of questions useless, and the also the type that the CG, in the infinite lack of wisdom, enjoys.

If you are going to intercept a moving vessel to render aid, have it change course towards you. As for the 2nd, who cares what the maximum CPA is? You want to be as far away as possible (and we haven't even gotten into the question of navigable semi-circle, etc.) Sometimes, if searoom and other factors allow, the best course is to cross the path and get into the navigable semi-circle.

Hope I haven't upset some nice retired Coasties, but seriously folks, the CG should ask some decent, pertinent questions, or not ask any at all.
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Old 03-02-2010, 12:41   #4
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Thanks and my thoughts exactly!

My hunch is the intercept questions were modified from Naval maneuvering board situations - as it would certainly seem someone needing your assistance wouldn't continue steaming away from you.

If I suddenly find myself within 80 miles of the eye of a hurricane, I may have more serious skippering issues!

Alas, these are the questions I need to know how to answer.

Guess I can continue with my plotting practice, maybe I'll get faster through repitition.
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Old 03-02-2010, 12:58   #5
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There is a fast and standard plotting solution for these problems. Start reading at page 517: http://www.irbs.com/bowditch/pdf/chapt36.pdf That example specifically addresses the hurricane problem, but if you understand it it also shows you how to make a quick vector drawing to solve the intercept problems.

There are mathmatical formula that immediately solve both these problems, if you have a computer or calculator, but the plotting solution is the standard navigational approach.
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Old 03-02-2010, 13:00   #6
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Almost forgot--once you get good at plotting these things, you can solve many in your head by eliminating bad answers. In the first example you gave, a ship to your SE is traveling NE. Clearly the first two answers take you in the opposite direction. The third answer steers behind the vessel you want to intercept. 114 is the only reasonable answer.

Keep in mind that the test is checking for your understanding of maneuvering vectors. The context (hurricane, rendering assistance, etc) is irrelevant.

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Old 03-02-2010, 13:26   #7
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"If you are going to intercept a moving vessel to render aid, have it change course towards you."

Perhaps you are rendering aid because they have had a steering failure, or they are heading into the wind in order to keep smoke and fire from a stern fire from spreading further into the ship.

That's not imaginary, a cruise ship out of Florida had just such a fire in the stern laundry several years ago, and a couple of cruise ships in the NW had serious rudder failures not too long ago.

Or maybe you never heard the supposed pissing contest between two radio operators during a heavy storm one night, ending "We're a lighthouse, we suggest YOU ALTER COURSE TO AVOID US."
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Old 03-02-2010, 13:30   #8
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I knew one of the better seaman would have an answer, just to prove himself right.
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Old 03-02-2010, 14:32   #9
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The second question is interesting, don’t recall ever having to do this.

Through all my exams, from 2nd Mate to Master Foreign Going Unlimited tonnage, I have always approached these problems graphically, i.e. draw a plot, very similar to a radar plot. Don’t know about in the US, but in the UK, the radar plot consisted of the basic WOA triangle.
OA was the relative course and speed, WO was own course and speed and WA was target course and speed.
You know two of these vectors, and now have to find the third.

First question, the rendevous

On paper or chart of suitable scale, plot your position and call this “A”, plot the other vessels position and call this “O”
The line OA is the relative course and speed vector which has to be made to achieve a CPA of zero

From point “A” draw a vector equal to the RECIPRICAL course of the other vessel, and its speed (distance made in 1 hour). Or, you can use a period of 2 or more hours, whatever makes the plot easier, but make sure that this time period is also applied to all other vectors.
Assume you use a time period of 1 hour.

Label the end of the other vessels reciprocal vector has “W”.

Set a drawing compass to a distance equal to your vessels speed.
Stick the point of the compass in at point “W”.
Strike off an arc which intersects the line OA, and label this O1

The new line W O1 is the course you need to steer in order to acieve a CPA of zero
The distance A 01 is the relative speed which will be made between the two vessels.
Divide AO by A O1, and this gives you the time to intercept

Clear as mud!!

Second question
Never had to do this, cant see the point, if a TRS, take the usual avoiding manoeuvers.
Regarding intercepts, do this quite often if needing to meet up with a rig under tow in order to take over the tow from another boat, and they dont take kindly in being asked to alter course towards you, its all down to dollards and cents for those guys
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Old 03-02-2010, 15:35   #10
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Gentlemen,
You have given me exactly what I needed - thank you!
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Old 04-02-2010, 11:05   #11
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Quote:
Originally Posted by fmastin View Post
Use plotting paper and a protractor and the answers are easily obtained.

But, as an Ocean Master with many years of steaming around the world under my belt, I find these type of questions useless, and the also the type that the CG, in the infinite lack of wisdom, enjoys.
Just an aside to this. I've been involved with radio, military, commercial, and amateur for a long, long time. Licenses are required for various things. In the "old days" when I held a 1st Class Radio Operator's License (highest class in those days for a commercial license) it was the same way THEN.

Remember the "government authorities" for this are always constrained by "government bureaucracy" and thus, they complicate questions on tests to make sure "you can understand the material well enough to answer the question".

UNFORTUNATELY, they don't want to ask a plain English question. You see, then ANYONE could "pass".

/sigh
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Old 24-02-2010, 12:44   #12
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Passed the exam gentlemen. Thanks for your help - I had never used a maneuvering board before and it was interesting. Helped me solve a number of different types of questions on the exam - current set and drift, true versus apparent wind, intercept courses, and closest point of approach.
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Old 24-02-2010, 14:43   #13
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CONGRATULATIONS!!!
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Old 24-02-2010, 16:26   #14
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Nice work! What are your plans and which license did you get?
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Old 01-03-2010, 07:21   #15
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Got the OUPV and plan to charter my 46 ft cutter. Will be in the the Long Island and New England areas in summer, and go south in winter. Thanks for asking!
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