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» Online Classroom   »   » Public Discussion of Inland and Coastal Navigation   » Problem 5-16

   
Author Topic: Problem 5-16
Sandy Englehart


 - posted January 20, 2005 12:50 PM      Profile for Sandy Englehart           Edit/Delete Post 
When I ran this problem, I came within 1/3 of a mile of the answer, but that seems like a lot considering how careful I was. My last estimated position corresponded with N48-12.95m and W123-09.2m. When I advanced my first LOP to pass through that point, I ended up at N48-11.45m and W123-09.9m. I am not using the starpath calculator.
David Burch


 - posted January 20, 2005 04:53 PM      Profile for David Burch           Edit/Delete Post 
I have worked the problem again, and get remarkably close to the answer given. Here is the plot that I made using an echart program.

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You are right, however, that 0.3 nmi is too far off. Can you please look over this plot to see if you might find your error. Sometimes it pays to start all overagain, rather than looking for errors in individual steps.

Note that in this problem, i started with an LOP that was a meridian at the first light and then for the second could simply draw in a meridian line to form the second LOP. (ie, waypoint 1 of the DR segment is due north of the first light) --david

From: Starpath, Seattle, WA
Sandy Englehart


 - posted January 21, 2005 08:49 AM      Profile for Sandy Englehart           Edit/Delete Post 
I used magnetic north where I see you used true north. I imagine that is my error. Is there some clue I didn't catch so that I would know to use true direction? Thanks
David Burch


 - posted January 21, 2005 12:54 PM      Profile for David Burch           Edit/Delete Post 
Good question in this case. The problem starts off with an estimated position "directly north of Ediz Hook Lt." That type of phrase implies a true direction. When ever you hear "north" or "east" etc, without any further specification, it is perfectly fair to assume the meaning is true, not magnetic.

So we start off due north (true) of a light, and then it becomes easy becuase the courses in the problem are labeled specifically as magnetic, ie 088 M, etc. Had these been true, it would have been written 088 T.

From: Starpath, Seattle, WA
M. C. Rowley


 - posted September 26, 2005 06:36 PM      Profile for M. C. Rowley           Edit/Delete Post 
I was doing fine with the Section 5 problems until I got to this one. Could you please explain the steps involved to solve this problem (both manually and using e-chart).

Thanks....stumped in Santa Fe.

Mark

David Burch


 - posted October 21, 2005 12:18 PM      Profile for David Burch           Edit/Delete Post 
Sorry for the delay in responding. we have been in Annapolis boat show then meetings in CA, and somehow we did not get an automatic notice of a new message.

i have annotated the graphic with green lines to show the steps [A] to [F]. note that the actual target of the first observation is not on the picture.

the procedures by hand and by echart are the same. The only difference is drawing the lines by hand on paper or by range tool on a digital map. The use of echarts for this type of solution is described in the instructions to our echart supplement program. That is available as an add on if anyone wants it from echart supplement software, which as a download is $39. It includes a convenient echart viewer and 4 echarts of the region of our chart problems.

From: Starpath, Seattle, WA
jorge


 - posted January 09, 2008 10:46 AM      Profile for jorge           Edit/Delete Post 
I am up to the Electronic Navigation chapter in the course and I don't remember reading using the running fix in the way it is used in this problem (5.16). Is this covered later on or am I missing someting? I thought the running fix was on the same target while on a steady course.
David Burch


 - posted January 09, 2008 11:05 AM      Profile for David Burch           Edit/Delete Post 
We have started a new topic on this called running fixes and posted it in the Student Discussion Forum.
From: Starpath, Seattle, WA


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