Going Further in Celestial Navigation (The Sunline)

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Going Further in Celestial Navigation (Part 2: The Sunline) This video is part of the “Going Further in Celestial Navigation” video series. Part 2 of “Going Further …

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19 COMMENTS

  1. Awesome Videos…found many in here, but yours is interesting, clear and point to point. Keep up the good work mate. Its helping me to get through my 2nd mates exams. Thanks a Bunch

  2. THANKS A LOT! ALTHOUGH WHEN I TRY TO USE THE FORMULAS FOR DIRECT COMPUTATION OF SUNS ALTITUDE THE RESULTS ARE DIFFERENT FROM WHAT YOU GET ON THE BOOK. BUT STILL FINALLY, I KNOW HOW TO USE THE SIGHT REDUCTION TABLE. 3 YEARS AT SCHOOL OUR TEACHERS NEVER TOLD US ABOUT THAT BOOK AND WHEN I WAS A CADET ON PCC VESSEL MY OFFICERS REFUSED TO TEACH HOW TO USE THE BOOK.

  3. I tried it. I struggled. I made some mistakes but I learned. I was dumb enough to think the Getting Started videos were all I needed but because I'm inland I had to use an artifical horizon. Problem was that at hight of Summer the observed angle was outside the 120degree range of the sextant (being double the actual elevation). So I tried taking the sight later in the afternoon when the sun was going down. But using only the Getting Started videos I fixed my position way down towards Antarctica; wrong! I then realised the Getting Started videos were ONLY meant for noon sights. That was my "dumb" bit. Oops! So I used the Going Further videos. I thought I had to make a dip adjustment for the 217m above sea level; wrong! that dip adjustment is for the difference in height between sextant and the horizon you are using. But perhaps in the case of an artificial horizon this may not even be necessary since the angle subtended between the optical paths is divided by 2 and the effective horizon is at the height of the sextant by default. I'd be interested in an expert view on that speculation.
    I stuffed up the LHA calculation but discovered the problem when I sketched the earth in plan view and could then understand and apply the LHA rules for my East longitude.
    GPS and my own Fix differed by 3.7nm For a first attempt I happy with that. Thanks to Chris from SV Navigator. Your videos got me over a number of mental blocks I've had for years on this topic.

  4. I have taken the time to learn doing site reduction with calculator. I like the books and all, but you get so much more accurate plotting with precise DR's.
    chriss, any recommendations on sextant brands? I use a Davis MK15. it's ok. would love to add a bubble, but can't find one. was thinking of building a DIY. what brand do you use. any thoughts on plastic vs metal. they must make light weight aluminum????

  5. chris, love videos. this combined with books and I have no difficulty plotting sunlines. Question(I hope you haven't answered already ), it's stormy, no sky for days. if your DR is way off, let's say 100 miles, will using Bad APs (way away from True) lead you back in right direction? how far off will your fixes really be? I'm sure the father your off, the greater uncertainty, as the true LOP are curved?

  6. Great job Chris, gone from 0 to understanding how to calculate my LOP with the sun and a handful of stars in a few weeks, thanks to your tutorials. If you drop by the Marseille area, drop a line!

  7. When correcting for the unaccounted minutes of declination at 8:21, instead of using tables can you just multiply your extra minutes by the slope of the curve at that point. ie, (30unaccounted minX1deg/60min)X(-17.9min/deg)= -9 min?

  8. Hello Chris, I computed my first sun line position today and came within 8.2 miles of my GPS position. I was stoked. When I took the observation, the sky had a high, thin cirrus cloud layer that made the sun fuzzy when brought down to the horizon. I feel confidant that with practice and a better observation, I'll be able to increase the accuracy. Your videos are awesome. You make a complicated process seem simple and that is a gift. Keep up the good work.

  9. Hi Chris, I missed the part where you said why correction for azimuth angle is not really important. It seems as if that angle is generated bases on the values you enter for your assumed position, which is somewhat sketchy to start with as it depends on dead reckoning. And on top of that you make adjustments to these values of your location to make the arithmetic simpler. Doesn't the assumed position determine the azimuth angle to the  celestial body, and this in turn wouldn't this change the position of the LOP (which is perpendicular to the bottom side of the triangle (?zenith distance). I hope I worded this clear enough for you to understand my confusion. Thanks, much, Rob

  10. hey chris i know i've commented on the videos before. just wanted to say once again thanks for the videos. between you and another Australian guy i've been able to crash course myself to learning celestial nav. never really got into 229 but more using nories tables and subsequently just crunching the altitude and azimuth manually using a ten dollar four function calculator. just wrote the equation on the cover of the almanac (hell thought about just taping it to the sextants box) to make it idiot proof. but would love to see your take on this method.
       

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