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Old 04-11-2012, 04:49   #946
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Re: Paper Charts Now Unnecessary

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Originally Posted by noelex 77 View Post

Personally I prefer the opposite approach I always compare my DR and GPS positions. I find I learn much more that way- maybe the leeway is a bit less than you allowed for- perhaps the log slightly under reads on starboard tack. This sort of information makes you a more accurate navigator in the future.
How are you doing the DR without paper charts?
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Old 04-11-2012, 05:41   #947
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Quote:
Originally Posted by frank_f

How are you doing the DR without paper charts?
Fast and easy on a laptop. just create a new route and have that as your dr. Add tidal vectors to the route for ep. Quick once you get used to it. Not sure about plotters though.
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Old 04-11-2012, 06:10   #948
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Re: Paper Charts Now Unnecessary

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Originally Posted by wolfenzee View Post
If a GPS says that (due to conditons) it is accurate to 30meters the computer will not draw a circle with a 30 meter radius (have seen as much as 245meters and no less than 5meters) but put your location in the center. Chart platter direction is based on the direction you are moving not the direction you are pointed otherwise current software could figure out the effect of the current, no piece of software can figure in the effect of the wind because of the variables involved a person can only do it with an in depth knowledge of and experience w/his boat.
A friend of mine ended up on a reef because he was relying solely on what his GPS told him

One of the best thing a chart plotter can do -- if you're not over-reliant on electrics -- is pinpoint things like drift and leeway. If you actually plot what you get from the chart plotter on to your paper chart, and actually attempt to predict where you will be in, say, an hour, and then compare your prediction to what the chartplotter finds, you'll notice when you're not taking all variables into consideration.

If you're smart, and in strange waters, you'll also gather local knowledge. I came up the same river three days ago that bent my rudder five months ago, and with local knowledge, was able to avoid the problem -- and understand how it happened last time. This river's channel has shifted very significantly and in fact markers 5 and 6 are no longer even there. (The paper chart is just as out of date.)

The title of this thread says it all. People who think chart plotters have replaced paper are in my opinion making a big mistake that could cause them a very serious accident some day, but the problem is that people don't know what they don't know. They don't know what they're missing, as it were.

And, if you plot your course on a chart using both your own skills and the electronics, not only will your non-electronics skills go up, but if your chartplotter goes belly up, you'll be much better able to deal with it.
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Old 04-11-2012, 06:13   #949
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Re: Paper Charts Now Unnecessary

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Originally Posted by wolfenzee View Post
If all input is manual than the only differance is the fornat of display

One advantage would be that you could still zoom out for the big picture and then zoom in again for details. It reduces the number of times you have to whip your reading glasses out, and takes up a whole lot less space in a cockpit (where it needs to be near the coast) than a chart, but I think a computer program with a manual overlay feature would be a lot more practical.
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Old 04-11-2012, 06:21   #950
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Re: Paper Charts Now Unnecessary

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Originally Posted by Andrew Troup View Post
Well, yes, that's the point of my question. How much can I draw, at my discretion, and how easily?

If I'm using a paper chart, and I read in the logbook, after a rough night watch, that crewman "X" reckons he's been trying for 185 but only made good 192, I might draw two lines on the chart, one at 190 and one at 200. (This may include an allowance for leeway based on conditions and past experience). I might shade between the two lines to make it clear what they represent, especially if sharing the nav duties with another.

(If it was crew "Y", they might just log that they always make good the course ordered. I might however know from experience they don't do even as well as "X", at least, not on this trip.... in which case I'd draw a wider wedge after their watch. I'm not needing any help from the ship's computer on this, because as far as I know, the computer doesn't know about Y's marriage difficulties )

If there's a current, I'll do the vector addition to one of the lines, but then slew them both.

Then when we cross an ocean ridge at a suitable angle and the soundings give me a rough distance along that wedge, I draw a rough box or ellipse on the chart to cover the whole range of our probable positions. Or I might get a bearing on a distant lighthouse, which I know might be plus or minus 3 degrees out: similar sort of process (a wedge of two lines crossing the first wedge, and the ability to selectively shade or somehow indicate the resulting position box)

If I don't get a better, tighter fix, the worst position in that moving, growing box, in respect of any danger, is where I will assume us to be when planning when to come onto a new course to clear that danger.

Now, earlier in this thread the assertion was made on several occasions that this type of manual-input navigation was easier and better with a chartplotter than with a paper chart.

If that was not the case, then this thread becomes somewhat pointless, because it becomes a subtopic of a higher level "Should we place sole reliance on GPS and forget about navigating and pilotage?" topic.

If the answer to that question is "No" (and for me it is) and the answer to my question about plotting evolving uncertainty of positions on a chartplotter is "No can do", then for me the answer to the question "Are paper charts now unnecessary has to be a resounding "No".
I don't recall anyone saying you can manually mark the chart on a chart plotter. I have said multiple times that a paper chart should still be used and marked. Maybe that's where the confusion comes from?

Also, if I were doing an ocean crossing on someone else's boat (wouldn't attempt it on mine), I would be marking the chart as the skipper instructed me to. Honest to goodness if I were ever to the point that I were doing that on my boat and someone did *not* mark the chart as instructed, they'd be off the boat as soon as I could arrange it. To me that would be unconscionable, like arbitrarily picking a new destination for the boat in the middle of the night.

If the person were honest and said "I'm sorry, I fell asleep," I understand that we're all human and all make mistakes (although I would want enough crew for two on a watch someone may have gotten sick or something). But to just mark the chart differently? No way. I wouldn't want to go to that chart 18 months later and try to figure out what that person's marks made, or find empty spots on it.
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Old 04-11-2012, 06:25   #951
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Re: Paper Charts Now Unnecessary

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Originally Posted by Ex-Calif View Post
I don't disagree but how is this used in navigation?

If I am reading right there is a question that says basically, I am here, in the future I will be in this cirlce of error based on wind, waves, nav error etc. Is the wind error what we are saying the computer cannot predict or calculate?

Because if you can reduce the effects to mathematical constants or even a combined factor one should be able to...

I'm not so sure everything can be reduced to numbers. Circumstances can change pretty quickly. Also on a long passage, won't you have multiple crew on watch? Will they all have that ability to reduce all judgments to numbers?

Comparing your estimated lat and long to what the chart plotter tells you will spot errors very quickly. Then use your best judgment to predict where you will be in an hour, sail without the chartplotter guiding you, and then look at it in an hour and see how accurate you were. The mistakes are even predictable if, say, you weren't aware of a current.
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Old 04-11-2012, 06:27   #952
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Re: Paper Charts Now Unnecessary

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Originally Posted by noelex 77 View Post
For full time "traditional" navigation like this I would much prefer paper charts.

However there is no great difficulty doing what you want on most electronic charting systems. Some of the techniques will be different, shading for example is not possible but there are other ways of doing this such as using different colours etc that are not possible on paper chart.
If you have a particular requirements the talented people in the open CPN forum will write a program so it will do just what you want.


On comment I would make is I think it's much better to use the technology, for example using a GPS position to determine what the true COG has been for the watch will help your helmsmen in the future to estimate more accurately what course they have been achieving, even if they have marriage difficulties

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Old 04-11-2012, 12:27   #953
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Re: Paper Charts Now Unnecessary

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Originally Posted by frank_f View Post
How are you doing the DR without paper charts?
The purpose of DR is to figure your position with out any position input such as sextant, GPS, landmarks etc.....a plotter uses input from GPS which makes DR unnecessary....if you have no input as far as a position fix using electronic charts instead of paper charts is just a matter of display.
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Old 04-11-2012, 12:29   #954
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Re: Paper Charts Now Unnecessary

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Originally Posted by Rakuflames View Post
One advantage would be that you could still zoom out for the big picture and then zoom in again for details. It reduces the number of times you have to whip your reading glasses out, and takes up a whole lot less space in a cockpit (where it needs to be near the coast) than a chart, but I think a computer program with a manual overlay feature would be a lot more practical.
I have to whip out reading glasses to read my electronic display which is way smaller than my paper charts
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Old 04-11-2012, 12:31   #955
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Re: Paper Charts Now Unnecessary

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Originally Posted by wolfenzee View Post
The purpose of DR is to figure your position with out any position input such as sextant, GPS, landmarks etc.....a plotter uses input from GPS which makes DR unnecessary....if you have no input as far as a position fix using electronic charts instead of paper charts is just a matter of display.

But while developing those DR skills, comparing where you think you are with where you actually are is extremely useful.

It's a mistake to assume that all who have chart plotters either don't know DR or don't use paper charts. DR is a skill that develops over time, and truly, using a chart plotter is a lot more than a "matter of display." At least there's more than that to it when used intelligently.
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Old 04-11-2012, 12:32   #956
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Re: Paper Charts Now Unnecessary

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Originally Posted by wolfenzee View Post
I have to whip out reading glasses to read my electronic display which is way smaller than my paper charts

I zoom in, but at most resolutions, my chart plotter screen information is bigger than it is on the chart. I have a Garmin 441S.
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Old 04-11-2012, 12:45   #957
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Quote:
Originally Posted by Rakuflames

I'm not so sure everything can be reduced to numbers. Circumstances can change pretty quickly. Also on a long passage, won't you have multiple crew on watch? Will they all have that ability to reduce all judgments to numbers?

Comparing your estimated lat and long to what the chart plotter tells you will spot errors very quickly. Then use your best judgment to predict where you will be in an hour, sail without the chartplotter guiding you, and then look at it in an hour and see how accurate you were. The mistakes are even predictable if, say, you weren't aware of a current.
I think I finally get Andrews point - If I "always sail the GPS" and every time I record a fix, I have no idea what components of CMG are accurate helming, drift and set.

So I manually plot a course on paper - calculate my CTS and at next watch see if I am making good on the course. If my position is in error then my manual or ded reckoning plotting is not as good as it could be.

So one should be able to agree that always following the magenta line and never exercising the manual skills will allow those skills to atrophy.

Now transfer the exercise to the plotter - The data is there but may not be captured and utilized - Every split second, heading, CMG, wind speed, truwe and apparent etc, etc, etc is gathered. If that data were stored for a watch then the skipper could say - The course was 190, the CTS was 185, the helm steered between 180 and 195 and on average steered 188. We are X miles west from the predicted point so the 3 degree helming error explains the position error.

One could calculate the drift and set manually (based on known polars of the boat) "decide" that 188 is the course to steer and then steer 188 accurately. The error would be the same and one would still be off position.

What happens with the gps howver is that CTS is constantly updated so in the previous watch cited the CTS would gradually chang from 185 to 184, to 183 as the westerly error got bigger.

Seriously this is way easier using a plotter than paper.

So RF you =r second paragraph about estimated vs. actual is in agreement with this I think - Basically DR and verify periodically with a GPS fix (if one wants to do a celestial fix - that is an alternate)

However you first paragraph getting back to the boats numbers and predictability I would argue that they may not be calculable with high accuracy (that's what a polar does but many polars are not accurate - espoecially when the hull gets dirty, the sail gets old etc) but they can be predicted as one learns their own boat - i.e. if I sail on 60 apparent in 15kts my speed should be X and my set should be Y (based on history) so these numbers (the "real" polar let's say) can be reduced to constants, curve fits can be established and they can be stored in a computer so that creating a DR CTS can be more accurate than a human every will be.

When I took a racing seminar this year the instructor said - "Take a log book with you when you sail. Using the electronic aids available (gps, wind etc) start tracking the currents where you sail and plot them (on paper - yay) - over time you will build a bible of knowledge you can use in racing that will far outweigh any advantage in trimming better for another .5kt boat speed. The point being that most everything can be reduced to numbers

Once we get "off the historical" numbers (i.e. "conditions change") everyone is guessing and whether the human guesses (based on his/her saltiness) or the comuter guesses it is still a guess.
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Old 04-11-2012, 13:48   #958
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Re: Paper Charts Now Unnecessary

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Originally Posted by Rakuflames View Post
I zoom in, but at most resolutions, my chart plotter screen information is bigger than it is on the chart. I have a Garmin 441S.
I am a poor sailor and can't afford more than Nobeltec 6.5 on an laptop.

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Originally Posted by Rakuflames View Post
But while developing those DR skills, comparing where you think you are with where you actually are is extremely useful.

It's a mistake to assume that all who have chart plotters either don't know DR or don't use paper charts. DR is a skill that develops over time, and truly, using a chart plotter is a lot more than a "matter of display." At least there's more than that to it when used intelligently.
This also works for developing your celestial navigation skills or for that matter any form of "analog" navigation.....functional electronic navigation can be very helpful when learning to navigate when the electronics aren't functional.
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Old 04-11-2012, 14:35   #959
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Re: Paper Charts Now Unnecessary

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I think I finally get Andrews point - If I "always sail the GPS" and every time I record a fix, I have no idea what components of CMG are accurate helming, drift and set.....

Thanks for hanging in there, Dan - I know I'm inclined to be wordy when I should be concise, and vice versa

However your first paragraph getting back to the boats numbers and predictability I would argue that they may not be calculable with high accuracy (that's what a polar does but many polars are not accurate - espoecially when the hull gets dirty, the sail gets old etc) but they can be predicted as one learns their own boat - i.e. if I sail on 60 apparent in 15kts my speed should be X and my set should be Y (based on history) so these numbers (the "real" polar let's say) can be reduced to constants, curve fits can be established and they can be stored in a computer so that creating a DR CTS can be more accurate than a human every will be.......
When you say "set", I'm guessing that's your word for what I call "leeway"?

(To me, "set" is an influence on the boat's progress which is of external origin, specifically from a current)

I struggle a bit with the notion of predicting things like leeway from a lookup table based on historical data. It's so much influenced by things which are hard to quantify, such as seastate.

Even windstrength, reduced to numbers, is a poor guide: the density of the air varies considerably with temperature and humidity, and spray content; but I also find that turbulence can drastically alter the relationship between lift and drag. At home we have a foehn wind which is 'micro-puffy', which to the ears feels like multiple gusts per second, and means that laminar flow is never really established. 30 knots of this rubbishy landlubberly wind has you going sideways much more than 30 knots of solid, treacly, dense polar airmass.

I think intuition can be a more reliable (and certainly much faster) tool than analysis in complex, unquantifiable and dynamically evolving situations. PROVIDED the intuition is guided by detailed and painstaking prior observation.

More controversially, - and perhaps applicable mainly to people like me, for whom understanding does not always come easily - it can also be guided by hard yards of intellectual rumination and post facto analysis, trying to make sense of outcomes from complex situations previously encountered.

Hence my painstaking process in, say, trying to come up with a detailed and plausible explanation of paradoxical lee helm in another thread. I think I do this in an attempt to 'preload' my intuition, as well as to satisfy my curiosity.

I wonder if I come from a different place in a 3D continuum of sailing space from you: I don't race much these days, I'm often on different vessels, etc etc...

None of which put a premium on accuracy, or sustain gathering information in the formal way you suggest.
I think this explains why my focus is not on being as accurate as I can be, so much as keeping tabs on what is likely to be my maximum inaccuracy.

Key decisions can then be made from a 'worst case' assumption within that mobile zone of likely positions, and that assumption needs to be re-assessed in the context of each fresh decision.
Eg: "If we tack, position A is our worst case; whereas if we stay on this tack, it's position B"

My estimation of inaccuracy does not itself have to be accurate, provided it's suitably conservative.
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Old 04-11-2012, 14:48   #960
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Re: Paper Charts Now Unnecessary

The most gifted navigator I've ever met (and I've been lucky enough to sail with a couple of the most famous) was a relatively unknown guy - at least in the Anglosphere - called Jérôme Poncet.

People who sailed with him a lot described how he could wake after being deeply asleep for the duration of several watches, and instinctively have a good idea of the vessel's position.

I guess somehow, having sailed to challenging places all his life without external nav aids, he had become so attuned to the way of a yacht that his unconscious could process the motion of the vessel and infer changes of heading, and keep a sort of running DR.

But even during his days as sailing master on racing yachts for Giorgio Falck, he was never one for recording or sailing by numbers.
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