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» Online Classroom   »   » Public Discussion of Cel Nav   » WT vs GMT

   
Author Topic: WT vs GMT
Rich A


 - posted April 05, 2017 05:27 PM      Profile for Rich A           Edit/Delete Post 
I have a feeling this is a frequent flyer question, but here goes:

If you leave from Seattle to HI in the summer (WT+7 and WT+10), why do you not change your WT to match the time zone?

In HBS we used WT+7 throughout the exercise, but as we navigate west we pass through ZD areas of WT+8, 9, and eventually 10.

Because we use GMT for DR-specific sights, why did the correction to WT not reflect the transition into/through different time zones?

From: Lacey
David Burch


 - posted April 05, 2017 08:11 PM      Profile for David Burch           Edit/Delete Post 
in cel nav you only need UTC. It is safest and simplest to not change your navigation watch once underway.

We have discussion of this philosophy in our text book.

http://www.starpath.com/catalog/books/1887.htm

and in the glossary (starpath.com/glossary) see UTC, WT, ZT etc

and in online articles,

http://davidburchnavigation.blogspot.com/2012/03/timekeeping-in-navigation-and-weather.html

From: Starpath, Seattle, WA
David Burch


 - posted April 05, 2017 08:14 PM      Profile for David Burch           Edit/Delete Post 
Maybe the more basic answer is, UTC = WT + ZD. we keep the ZD fixed. then that is always the way you get UTC, regardless of where you are in the world.

then see various notes cited we have on why it is bad to change time zones to match the local time the fish are keeping.

From: Starpath, Seattle, WA
Rich A


 - posted April 05, 2017 10:50 PM      Profile for Rich A           Edit/Delete Post 
Looking back over the question I phrased it wrong.

I meant since the ZD in Seattle is different than west towards HI, why do we not adjust the ZD on the worksheet to match our DR longitude?

The sight readings (for the same celestial body) 150 east of HI are different than the readings taken at Cape Flattery at the same time - is that correct?

If so, then wouldn't applying a ZD+7 150 miles east of HI give you an erroneous answer on the worksheet?

From: Lacey
Rich A


 - posted April 05, 2017 10:58 PM      Profile for Rich A           Edit/Delete Post 
Never mind .. I get it now. I just had to walk my way through it.

Thanks.

From: Lacey


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