NavList:

----- Original Message -----

From: Anabasis75@aol.com

To: NavList@fer3.com

Sent: Sunday, June 01, 2008 12:41 PM

Subject: [NavList 5236] Re: Exercise #7 LOP's

 

I suppose I could re-work it using 229 if you want the increased accuracy, though I'm not quite clear (yet...) on how to do the DSD interpolation. But I am working my way through Susan Howell's book (among others), and hopefully she'll explain that as clearly as she does the rest of the material.

 

JCA- Double second difference usually rears its ugly head with really high sights, but fortunately it did not happen in this case.  Frankly, the difference is minor enough that my sight errors are greater then the increased accuracy, that I tend to ignore it unless I'm on a USCG exam.  Even there, I am using my calculator (the formulae are in the preface) and just double checking with the book.  I'll review it a bit more and see if I can't do a small write up for you.  Heck, I might just shoot a high altitude sunline and see if I can't get it to want a DSD correction.

 

Hah, one thing that I've learned from teaching other stuff is that the teacher should always be one step ahead of the students. That's OK, we'll just drop anchor and wait for you...  ;-)

 

JCA- I had done it on the bridge when I shot it using my Almanac and calculator, but just not an AP position.  I have since posted it obviously.  Actually the most annoying part is typing it up.  Doing the sight took only a minute or two with my pencil.

> Actually, no these are independent sights, not meant to be run although

> there is no harm trying. 

 

Ah, OK - that would explain why there was nothing about running one LOP up/back to the other DR position.

When I do a star fix or running fix, I will certainly make it clear what I want in the question itself and I will also give a Course and speed so that we can all advance/retard the lines in the same way.

 

> The ship was moving at about 14.6 kts during these 2 sights, but we did a

> lot of turning and strange courses during those hours. 

 

Must have been, to only have that little net distance made good in that time frame.

 

> The Jupiter sight is actually part of a AM star fix which I will post in a different

> exercise, so don't lose it lol.

 

If I did the math right, these sights were taken in timezone GMT +9 (or ZD -9) and your DR longitude is ~9h40m fast on Greenwich. Interpolating the NA sunrise time for that day and 15 degrees N in my head, looks like this one was taken about 4 minutes before local sunrise (which I guesstimate roughly to be ~5:18 AM)?

We keep ZD -10, but yes, it was the last AM body I shot that day as it was the brightest.  I soon followed that with a LAM (what my friend and I call meridian transit of the moon) crossed with an AM Sunline.  That will also be a separate exercise.

Yeah, that should improve the accuracy considerably - and it dawned on me after I sent that e-mail that a running fix is just that, a "rough" fix with a DR plot being used as one of the LOPs. So now I don't feel so bad about being 3-4 NM "off" from the computer's results.  :-)

JCA Quite typical for long delays between lines.  I try not to advance or retard a line more then an hour or 2 unless really necessary.

 

BTW, what exactly are we doing in the vicinity of Saipan - practicing maneuvers, or maybe island hopping dropping off supplies?

JCA We were underway on manuevers which includes engine tests and running close to islands for cellphone coverage, etc.  The biggest issue as far as Celnav goes, is that without being on solid courses over a day, you can't really advance lines without a lot of extra math.

 

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