|
Author
|
Topic: Question 9.4
|
Bg
|
posted August 24, 2010 07:49 AM
Hello
I am having a little difficutly in getting to the answer in 9.4 on the plotting sheet. I did both the plots but I am not sure how the advanced 7:50-1150 lands up where it does. What I did was take the distance travelled between the 2 times (25.09miles) and then use my parallel rulers to transfer over the moonline at 7:50 to the 11:05 sunline with a distance of 25.09 miles but I suspect I am doing something wrong. Could someone please tell me where I am making my mistake.
|
|
David Burch
|
posted August 24, 2010 11:50 AM
There is a plot of the answer on page 201.
Are you asking if this plot might be wrong, or maybe did not know it was there?
From: Starpath, Seattle, WA
|
|
HHEW
|
posted August 24, 2010 12:14 PM
How much is your fix off? The only thing I notice in the info you give is that your distance run of 25.09 NM may be off. I get the difference between the two times (0750 & 1105) as 3h15min or 3.25 hours.
3.25 X 7.8 knots = 25.35 NM.
-Hewitt Schlereth
|
|
Bg
|
posted August 29, 2010 07:22 AM
What I did was measure the distance with my dividers from 7:50 to 11:50 the distance run, draw a parallel line to the 750/1150 line at the same distance of the dividers and then transfer my moonline over to get a fix. I was out by about 2 degrees north. I see what you are saying about the 25.35 NM I still don't hit it on the same mark as the answer. Is the procedure that I am following correct?
|
|
HHEW
|
posted August 29, 2010 11:22 AM
Along what line did you measure the distance run? It sound like you may have measured it perpendicular to the 0750 moon LOP. The distance run should be measured along the course line, starting from the point where the course line (335°) crosses the 0750 moon line. Look again at the school's plot on page 201 of the text.
-Hewitt Schlereth
|
|
Bg
|
posted September 01, 2010 07:29 AM
I measured the distance run from the Course line named "DR Track Before Sights" from the 7:50 to the 11:05. I realise I must be wrong now but could you tell me what to do to get the advanced moon line where it is please?
|
|
HHEW
|
posted September 01, 2010 05:23 PM
Please let us know what your fix is.
Also, is your central latitude 45° N and your central meridian 123° W?
I'm asking this so we can be sure your UPS plot is set up the same as the school's.
-Hewitt Schlereth
|
|
Bg
|
posted September 08, 2010 07:44 PM
Apologies for the delay in answering
My answer came to 45deg 16'N and 123deg 15'w
My central latitude was 45 deg and my central meridian was 122deg
|
|
HHEW
|
posted September 09, 2010 07:06 AM
Well, your fix (45° 16' N, 123° 15' W) was not at all far from the school's of 45° 14.5' N, 123° 17.3' W.
If you consider that the school's fix was, as the parenthesis notes a calculated one and round their result to 45° 15' N, 123° 17' W, you're maybe a tad high (say 1') on the longitude. Not all that bad, really.
The main thing here though, is you've obviously got a pretty firm grip on celestial in general and plotting in particular.
If you should want to rework this one, I'd suggest 1) Making the printed central meridian 123° W, which will eliminate any possible glitch in drawing in 123° slightly off. 2) If you're using a parallel rule to lay out a course line from the printed central rose, use a protractor to check that it crosses a printed longitude or latitude line at the angle it should. 3) If you're advancing the LOPs with a parallel ruler, use a protractor to check that the advanced LOP crosses a printed longitude or latitude line at the same angle the un-advanced line did. 4) Be very sure you are not mixing up the latitude and longitude scales when measuring with dividers.
-Hewitt Schlereth
|
|
Bg
|
posted September 11, 2010 11:57 PM
Thank you for the answer, I am just happy to know that I have the procedure correct. I will try another example with the central meridian as 123 deg and will double check my work with the protractor.
|
|
