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Old 14-10-2012, 19:28   #826
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Re: Paper Charts Now Unnecessary

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Originally Posted by Celestialsailor View Post
Magnetic Variation is due to the differing positions of the Geographic North Pole and the Magnetic North Pole. The boat's compass and a hand bearing compass point to the Magnetic Pole, but all bearings on charts are related to the Geographic Pole (True North).
CelestialSailor - Downunder's repost of this reminded me about this statement and I was wondering where the copy paste came from.

I am not sure if this statement is true.

The lines of lat and long are aligned true north.

The compass rose on charts is aligned to mag north.

If one transfers a course/bearing using protractor and parallel ruler from the lat/long lines it is true heading.

If one transfers the course/bearing from the compass rose it is in mag heading.

For the Navigators out there -

It seems logical to simply transfer mag course from the rose to the rhumb line however there are two reasons (at least) to not do this.

1 - The rhumb line is long on a large scale chart and covers multple areas of mag variation - i.e. the mag variation will change over the course of the journey.

2 - The chart is old and what may have been a 14E variation is now something else - i.e. 16E.

Now the reality is that no one on a small boat is holding mag heading within 2 degrees especially with mag compass dip errors (acceleration and turning errors) so it is sort of a non-issue but it is technically correct...

Navigation is fascinating stuff...
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Old 19-10-2012, 20:57   #827
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Re: Paper Charts Now Unnecessary

coming down the coast a couple of weeks ago, Hand held GPS put me on the beach (not literally, i was a couple of knots off but when i plotted the co-ords that was where i was supposed to be - thats pretty normal for my sextant sights but i was not expecting it from the GPS) never had that happen before. Glad it was middle of the day and i already knew exactly where i was - cautionary tale.
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Old 19-10-2012, 21:51   #828
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Re: Paper Charts Now Unnecessary

A prudent marniner never relies solely on one method of navigation.
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Old 19-10-2012, 22:18   #829
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Re: Paper Charts Now Unnecessary

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I was talking to Lin Pardey about this matter at the wooden boat festival..she had been onboard a racing boat, the skipper wanted to leave the paper charts ashore. She pointed out the paper charts showed land topography and the electronic charts didn't... the topography of the islands affects the wind which was very important in racing.
The topography of the land is also crucial information for pilotage, surely?

Even with paper charts showing topology:
because GPS tells us where we are, we risk losing the ability in infer our position from land features.

This is a totally different and far more difficult activity when we DON'T know where we are, than when we do, and this ability risks withering on the vine if we don't make a practice of keeping it current.
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Old 19-10-2012, 22:41   #830
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Re: Paper Charts Now Unnecessary

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Originally Posted by Andrew Troup View Post
The topography of the land is also crucial information for pilotage, surely?

Even with paper charts showing topology:
because GPS tells us where we are, we risk losing the ability in infer our position from land features.

This is a totally different and far more difficult activity when we DON'T know where we are, than when we do, and this ability risks withering on the vine if we don't make a practice of keeping it current.
G'DAy Andrew,

I was never very good at this aspect of pilotage... those bloody hills all look alike to me unless they have "conspic" features.

So, thinking about your post, practice in observation and correlation to the chart when one DOES know about (or exactly) where one is seems like a good exercise. I'll be putting some effort into this on our next coastal passage (if we EVER get out bloody mast back!).

Thanks for the idea, mate!

Cheers,

Jim
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Old 20-10-2012, 03:15   #831
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Re: Paper Charts Now Unnecessary

I was sailing down the Algarve trying to get my wife into sailing, It was a beautiful night cruise up the coast, the wind was not to strong, the stars were out,alls well and were a happy crew until, the skipper came up and asked a simple question, can anyone see two red lights vertical, dutyiful we all looked towards the land , nothing doing??? in relays the four of us went below looked at the pilot and the paper charts, both said the same thing , back on deck now with a set of binos i scanned the area, no red lights , into my bag for my g,p,s, powerd it up yep same as the ships on, then i started to disect the land, block by block, nothing ,futher along we looked back and saw the lights two vertical where they should be , but some one had built a hotel in front of then, the moral of this story is never trust anything older than about six months be it paper or electric
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Old 26-10-2012, 15:26   #832
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Re: Paper Charts Now Unnecessary

I have a question. How many of you know celestial navigation?
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Old 26-10-2012, 15:36   #833
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Re: Paper Charts Now Unnecessary

There's a thread for that:

The New and Improved Celestial Navigation Poll

Gives you the general idea (self-reporting poll, so not scientifically valid, but should still answer the question somewhat).
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Old 26-10-2012, 16:29   #834
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Re: Paper Charts Now Unnecessary

Quote:
Originally Posted by Andrew Troup View Post
The topography of the land is also crucial information for pilotage, surely?

Even with paper charts showing topology:
because GPS tells us where we are, we risk losing the ability in infer our position from land features.

This is a totally different and far more difficult activity when we DON'T know where we are, than when we do, and this ability risks withering on the vine if we don't make a practice of keeping it current.

???

My chartplotter includes land features, just like my paper charts do.
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Old 26-10-2012, 16:56   #835
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Re: Paper Charts Now Unnecessary

So along the lines of this original thread, how many find the old pencil/pen line sketches of prominent land features found in the old coast pilots (and on some paper charts) to be more useful than something more modern in identifying distinguishing land features?

Even with new buildings/modernization I find these old sketches to be easier to apply/use. I suspect this is because they were drawn from the same perspective (i.e. in the offing, from a boat deck) and that the artists intentionally or unintentionally emphasized the most distinguishing features. Even in San Francisco Bay, with the tremendous amount of development that has occurred in the last 150 years most of the key landmarks are still very recognizable from these sketches.

Once you get closer, of course, having a modern picture with the current buildings makes things easier, but from a distance I find that the old sketches work better for me.

Anybody else?
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Old 26-10-2012, 17:39   #836
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Re: Paper Charts Now Unnecessary

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Originally Posted by Dsanduril View Post
So along the lines of this original thread, how many find the old pencil/pen line sketches of prominent land features found in the old coast pilots (and on some paper charts) to be more useful than something more modern in identifying distinguishing land features?

Even with new buildings/modernization I find these old sketches to be easier to apply/use. I suspect this is because they were drawn from the same perspective (i.e. in the offing, from a boat deck) and that the artists intentionally or unintentionally emphasized the most distinguishing features. Even in San Francisco Bay, with the tremendous amount of development that has occurred in the last 150 years most of the key landmarks are still very recognizable from these sketches.

Once you get closer, of course, having a modern picture with the current buildings makes things easier, but from a distance I find that the old sketches work better for me.

Anybody else?
Not sure if I would say more useful than something more modern. It would depend on what something modern might be, but in the past I have found the old sketches extremely helpful. Would not mind having that as an option in the future.
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Old 26-10-2012, 21:07   #837
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Re: Paper Charts Now Unnecessary

Here's a couple of piccys you can knock your selves out on,
when everything thing else has failed, Including compass,

This is all you may have left, its in the southern Hemishere,
Northern Hemisphere will be different stars,

and in the day, you have the sun to navigate by,
Its not accurate, but it will get you where your going,
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Old 27-10-2012, 00:40   #838
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Re: Paper Charts Now Unnecessary

If you have lost all your GPS units and compasses aboard a cruising boat it's likely you (or the world) have bigger problems, but its useful to find north when walking etc.

In the northern heamasphere its easy using the North Star in the southern heamasphere I use the pointers and southern cross.
The method is explained here
HowStuffWorks "Finding the True North with Moon and Stars"

The "watch" method which is also explained on the link is best during the day.
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Old 27-10-2012, 10:22   #839
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Re: Paper Charts Now Unnecessary

Because the same data is used in the creation of electronic charts (raster charts are actually scanned from the same source). So it's not a matter of one being more accurate than the other. The main gist of this thread is not are paper charts unnesary, but rather considering everything that chart plotters can do is it necessary to learn how to navigate...the answer is an unequivocal YES.
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Old 27-10-2012, 10:34   #840
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Re: Paper Charts Now Unnecessary

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Originally Posted by kiwitrucker View Post
I have a question. How many of you know celestial navigation?
I have a first edition copy of "The Complete Cruiser" the first section is devoted souly to celestial navigation, and the first sentence reads "Anyone who can add, subtract and read a railroad timetable can learn celestial navigation". I have another book also published in the early forties which is basically a simplified version of what the USN taught at the time and tells you how to figure your position without sight reduction tables. Celestial Navigation is one of those things in life that has been given a mystique...but is actually quite simple. Someone once told me celestial navigation is a lost art...it is not an art, but a skill the hardest part of celestial navigation is that it takes patience and requires you think....patience and thought are also lost skills in this push button culture of ours.
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