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» Online Classroom   » Inland and Coastal Navigation   » Public Discussion of Inland and Coastal Navigation   » 1210TR WB Prob 9-9 errata

   
Author Topic: 1210TR WB Prob 9-9 errata
Marksail2


 - posted March 05, 2020 11:05 AM      Profile for Marksail2           Edit/Delete Post 
Gentlemen,

In working through the exercises in the Navigation Workbook 1210 TR, Problem 9-9 specifically I think I found an error.
The solution given was Set 053 T and 1.13 Drift. I don’t see how this can even remotely be correct.

I’ve included MY solution clearly showing the Set to be 290 T and drift 1.29 kts over 2h10m giving an offset distance of 2.8 nm

If I’m wrong please forgive me. If so I’d like to know how I miscalculated.

Respectfully,

Mark Starr

From: Mark Starr
David Burch


 - posted March 05, 2020 11:08 AM      Profile for David Burch           Edit/Delete Post 
Thanks. we will look into this. the solution did not show up. if it was a graphic (the only option to typing it out) has to be <800 px across and size <300 kb
From: Starpath, Seattle, WA
David Burch


 - posted March 05, 2020 11:11 AM      Profile for David Burch           Edit/Delete Post 
Mark, Toby said he got the solution directly from you to helpdesk, and he will post it for you.
From: Starpath, Seattle, WA
David Burch


 - posted March 05, 2020 11:13 AM      Profile for David Burch           Edit/Delete Post 
Here it is.


From: Starpath, Seattle, WA
Capt Steve Miller


 - posted March 05, 2020 04:13 PM      Profile for Capt Steve Miller           Edit/Delete Post 
I worked the problem on the 1210TR chart. I found that the answer given at the end of the work book is correct at set is 54° and the drift is 1.13.

Looking at your work I noticed that you were using a traveling time of 2 hours 10 minutes. When subtracting the starting time of 0915 from the end time of 1045 the elapsed time is 1 hour and 30 minutes. You traveled 9 nm not the 13 nm that you were using.
Also, the True course is 90°, I do not know how you came up with 89.4°

Hope this clears up the confusion.

From: Starpath
Marksail2


 - posted March 06, 2020 08:23 AM      Profile for Marksail2           Edit/Delete Post 
A rookie mistake for sure! One that NEEDS to be learned at the drafting board NOT the Navigation table! Taking the two times 1045-0915 = 130 which I saw as 2h 10m. If I had done it correctly I would have seen 1h30m which in turn threw my STD calcs way off! Goodness knows if I had done this at sea where I would be ??? LOL That's why I'm working through these exercises.

BTW - again perhaps I'm wrong but my 1210TR chart shows a magnetic variation of 15degrees 15' W in the area of concern. Taking a 105M - 15.15 gives a heading of 89.45 degrees T That was my logic behind my solution. Was that in error?

It is my hopes that others learn from my simple yet serious mistake!

Wishing all calm seas and following winds!

/\/\ark

From: Mark Starr
David Burch


 - posted March 06, 2020 09:06 AM      Profile for David Burch           Edit/Delete Post 
Usually in the introduction to our workbooks we state what variation should be used for the whole chart... to simplify things. Also as a practical matter it is difficult if not impossible to do any compass work better than ± 1º
From: Starpath, Seattle, WA
Marksail2


 - posted March 06, 2020 09:42 AM      Profile for Marksail2           Edit/Delete Post 
My corrected solutions


From: Mark Starr
Marksail2


 - posted March 06, 2020 09:42 AM      Profile for Marksail2           Edit/Delete Post 



From: Mark Starr
Marksail2


 - posted March 06, 2020 09:54 AM      Profile for Marksail2           Edit/Delete Post 
Oops … arrow on graphic for current needs to be point TOWARD 54 degrees set.
From: Mark Starr


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