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Old 21-02-2012, 05:47   #1
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Plotting the Intercept

Quick question about doing the actual plot:

I'm confused about how to plot "away" vs. "toward". Is this a function of declination, so if the sun's declination is in the southern hemisphere, "away" is plotted away from south along the Z azimuth?
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Old 21-02-2012, 06:05   #2
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Re: plotting the intercept

Not related to declination: it's a function of whether height observed is lesser or greater than height computed. I use the little ditties: HOSA "Height Observed Smaller Away" and HOLT "Height Observed Larger Toward" to remember whether to plot Toward the GP (geographical position) of the body from my Assumed Position or Away from the body's GP from it. It helps, when you subrtract the one from the other on your worksheet, to write "Away" or "Toward" next to the sum to help you remember.
Hope this helps.
Ben
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Old 21-02-2012, 06:11   #3
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Re: plotting the intercept

Towards the body if Ho>Hc and away from it if Ho<Hc

If your altitude (Ho) is greater than the calculated altitude (Hc), then the intercept is plotted from the DR toward the body. if the Hc is greater than the Ho, the LOP is plotted away from the body
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Old 21-02-2012, 07:32   #4
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Re: Plotting the Intercept

2 ways to remember it: TTT (Tiny-er Tabulated Towards) and GOAT (Greater Observed Angle Towards). Tony
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Old 21-02-2012, 08:24   #5
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Re: Plotting the Intercept

Thanks. I get whether it's toward or away, I am just not sure toward or away from what.

I'm going to sound thick, but how do I know where the GP is? I'm using W.F. Buckley's methods plus HO249. I plot my AP, Azimuth and intercept to get a LOP, but Buckley is vague (in his book and on the video) about this part of plotting the intercept.
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Old 21-02-2012, 08:44   #6
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Re: Plotting the Intercept

reading your question tells me you need to take a course on celestrial navigation, you need a better understanding of what you are doing. this is not something you learn in a day. Just a 150 years ago it was a military secret.
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Old 21-02-2012, 08:58   #7
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Re: Plotting the Intercept

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Originally Posted by sailr69 View Post
reading your question tells me you need to take a course on celestrial navigation, you need a better understanding of what you are doing. this is not something you learn in a day. Just a 150 years ago it was a military secret.
give me a break.

That's not it at all. I can take an accurate sight, I can reduce the sight. My only question is about which direction I draw one line on a plotting sheet.

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Old 21-02-2012, 09:10   #8
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Re: Plotting the Intercept

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Thanks. I get whether it's toward or away, I am just not sure toward or away from what.
It's explained very well in Wikipedia incl. a diagram: Intercept method - Wikipedia, the free encyclopedia

ciao!
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Old 21-02-2012, 09:16   #9
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Re: Plotting the Intercept

Basically, which way do you plot the intercept.
In a way it's the error between what the book says and what your calculation gives.
If your OBSERVED Altitude is GREATER than your CALCULATED Altitude then the Intercept is TOWARDS..... the SUN.
In plotting your sun sight onto the chart....
a. Choose your GP (Geographical Position) LAT & Chosen Long and mark it on the chart.
b. From this position lay your AZIMUTH (Bearing) line |TOWARDS the SUN for the distance of the INTERCEPT.
c. Then draw a line at right angles to this bearing.... your position is somewhere on this line. (which is part of a great circle).

Need any further help then you can email me at ajmbwas(at)ntlworld.com and I can send you full info.
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Old 21-02-2012, 09:31   #10
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Re: Plotting the Intercept

So, it is about declination, after all? Got it.
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Old 21-02-2012, 09:46   #11
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Re: Plotting the Intercept

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Originally Posted by s/v Jedi View Post
It's explained very well in Wikipedia incl. a diagram: Intercept method - Wikipedia, the free encyclopedia

ciao!
Nick.
No, not really.
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Old 21-02-2012, 10:01   #12
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Re: Plotting the Intercept

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Originally Posted by sailr69 View Post
reading your question tells me you need to take a course on celestrial navigation, you need a better understanding of what you are doing. this is not something you learn in a day. Just a 150 years ago it was a military secret.
So like, he should go find a community of navigators, and ask them questions?
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Old 21-02-2012, 10:06   #13
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Re: Plotting the Intercept

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Originally Posted by sneuman View Post
No, not really.
I am apparently not allowed to quote from Wikipedia anymore, because my post which quoted part of the article and highlighted the relevant part was deleted. But be assured that the info is available on the link I provided earlier. Make sure to continue reading because it is further down the article.

cheers,
Nick.
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Old 21-02-2012, 10:20   #14
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Re: Plotting the Intercept

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So like, he should go find a community of navigators, and ask them questions?
What people posting these "take a course" remarks mean is that the OP is currently trying to master CN by following a method. This method is much like a trick that can be repeated, without really knowing what exactly you are doing and why you're doing these steps.

Everybody here knows that I can't live without the idea of people knowing things that I don't know but want to know... if that makes sense. Anyway, when I did my CN course I was 16 years old and it was part of the winter program of the sailing club my family was member of. I drove the instructor into bringing a globe and using strings show the class the circles on the globe of where you can be for a sight etc. If you get to the calculated position and geographic position and put those on the globe, you understand exactly what is meant with closer or further and which way the correction needs to go. It is this insight that is needed for me to accept theories and which is pointed at by the posters that make the remarks like explained above.

The question is what do you get when you go and take a CN class. I have heard stories where the instructor could hardly handle the DR part of it , so that wouldn't be very helpful for a sailor who is trying to get into CN later on.

Deckofficer hinted at how he draws everything out when he instructs his pupils so that would be the good way to get it. The instructor that I had in my class got wiser himself during our instruction and I saw him bring the globe to every later class too, so it obviously helps a lot to visualize it all.

ciao!
Nick.
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Old 21-02-2012, 10:24   #15
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Re: Plotting the Intercept

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Originally Posted by lolarose View Post
take star/sun/moon sight, read the sextant. that is geographical position (GP), moron.
Morons are "people" who sit looking at a TV all day, swapping channels as not to miss any good commercials. They are certainly not learning CN.

cheers,
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