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Old 05-11-2012, 01:03   #976
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Re: Paper Charts Now Unnecessary

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Originally Posted by Cookiesa View Post
I love when navigating tight channels etc is brought up and the enevitable story of a bad "gps" location causing someone to run aground.

Bet you the gps is more accurate and the position updated much quicker than anyone doing DR could do it, considering the data is the same, if the location of the reef etc is wrong or marks missing as already discussed then the odds are someone is going to come unstuck. Most sailers I know, regardless of the method of naviagtion they use do as already mentioned, ask for local knowledge, watch for tell tale signs on the water of impending danger and keep a good look out.

Very few would be marking their charts in this situation but rather concentrating on keeping the vessel safe.
This is a straw man argument, I think. I don't know any old school navigator who would for a moment consider using DR in a tight channel.

In close quarters combat, the methods switch to pilotage.

They'd be using clearance bearings, distance off (which they can calculate mentally from successive bearings off the bow and the log reading), transits (super useful when there's a cross-track set), back bearings, etc etc etc.
In unfamiliar waters, much of this can be pre-computed and taken to the cockpit, from where such pilotage can be done, at a pinch, while steering.
Certainly without going below.


If you asked for their DR update in such a situation these guys would look at you as if you were speaking a language they didn't understand.

(As an indication of how usable some of these methods can be in bad conditions: I often use transits when I'm swimming, and it can really save the day when trying to decode a rip current. Good luck using a GPS to work out which direction to swim when you're being dragged against your will into a surf break...)

I'm sorry to beat a dead horse here, but I don't think the following point has been explained fully:

Because local surveying was much easier to get 'spot on' than global position fixing in the pre-GPS era, the spacial inter-relationships of reefs and rocks to markers and landmarks and coastlines were likely to be MUCH more accurate and reliable than their position relative to any arbitrary global datum system (including the one they were supposed to use, based on Greenwich meridian and the equator).

By using similar methods to those who made the charts, we don't run the risk of datum (or "absolute coordinate system") errors.


NOTE: THIS RISK APPLIES PARTICULARLY TO PARTS OF THE WORLD WITH LOTS OF REEFS and ROCKS, and LITTLE IF ANY COMMERCIAL SHIPPING. There is no commercial incentive or return from resurveying charts in such places.

It also applies in places like parts of the subantarctic, where, for reasons of commercial advantage, the first sailors (almost invariably sealers or whalers) intentionally drew islands the correct shape and proportions (so they could use the charts for pilotage), but out of position (to limit the risk of competition for resource extraction).

Presumably they told favoured fellow-captains what correction to apply.

This is now thought to be one reason why so many sailing ships were wrecked on some islands, notably the Auckland Islands, where occasionally several groups of shipwrecked mariners were on them simultaneously, although they never found each other. (Travelling any distance is almost impossible due to the impenetrable vegetation)

In my own homeland, we have an extraordinarily long coastline. (Lots of "crinkly bits".) Particularly in the bottom left-hand corner, there are places only a handful of fishing boats (who know the place backwards) and a couple of yachts per year will go. The GPS is virtually useless on your first visit, but the chart is perfectly usable with pilotage techniques.

Much of it, until very recently, hadn't been comprehensively resurveyed since well before the American Civil War, and a few charts still haven't.

It was not at all unusual to find yourself notionally atop a mountain which makes Ararat look like a pimple.

Of course GPS is still useful, either by applying a datum offset once you've scoped out enough features to get a consistent figure (with caution and repeated checks once you start moving any distance from the area you checked out) but particularly to enable following your track back out of a place you piloted your way into, if the visibility has closed in meanwhile.
- - - - -

If you're in places like Tampa Bay or Long Island Sound, recent surveys will have corrected all this, and there will be negligible datum error.

But not everyone reading this forum sails only in such waters. Some of us go out of our way to avoid them.
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Old 05-11-2012, 01:29   #977
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Re: Paper Charts Now Unnecessary

Dan

By "wind leeway" I wonder if you mean what I would call "wind drift". This behaves like current set, but arises from a different cause: the movement of the surface layer of water downwind.

If you genuinely mean what's conventionally called "leeway", I'm personally rather queasy about treating it as a set.

That's because the units are different.

I'll explain what I understand leeway to be:

Leeway is caused by the need for the keel to present itself to the water at an angle of attack in order to generate a side force (which it has to do on any sailing course except DDW, to resist the side force from the sail plan, but in varying degrees). Quirky exception: A boat with a keel which can be slewed like a rudder could sail on any course without leeway. Such a boat can be set up to point the way it's going, even hard on the wind.

Consequently leeway is measured in terms of angle. It can be measured directly, say by pointing the boat directly at a pair of shoremarks which form a transit, reading the compass, then sailing for a few minutes on a heading adjusted to keep the shoremarks to stay in line, and comparing the two headings.
Naturally this leeway angle will hold true only on that point of sail, in similar conditions of wind and wave (and of course it's more complicated to measure if there's any cross-track tidal current, wind drift or ocean current)

But these last three things are measured in knots of speed, while leeway is measured in degrees of angle. I don't see any way of combining them, or any advantage in doing so.

Perhaps you have another name for what I'm calling leeway?
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Old 05-11-2012, 01:38   #978
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Re: Paper Charts Now Unnecessary

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Originally Posted by kiwitrucker View Post
In a lot of these post you guys have been using words and phrases, that myself as a newbie, have no idea what you mean. Reading between the lines I am thinking
1 It is a lot of what the skipper understands.
2 It is a lot of what the skipper is comfortable with.
3 If using only electronics have at least one independent back up.
4 have paper charts aboard for emergences.
Am I reading this correctly?
Yeah Kiwi, you picked up on it correctly. Occasionally we get carried away and sailor jargon takes over. Currently the discussion is endless (and probably closer to arguing religion than science) regarding the necessity of paper charts (as evidenced by this threads title). Bunches of skipper for charts, bunches against. Personally, I would't set sail without them, but then I'm old fashioned and like the feel of paper. Additionally I find they give me a better overview than my chart plotter. On the other hand, when navigating coastally, in tight waters (or at night), the plotter is invaluable. Which means I have, and use, both.

But I'm not religious about it - if others want to do it differently - peace be with them.

Having said all of the above, I still don't take my GPS word for everything. I know of several harbors where if I let my chartplotter decide, then I would sail straight onto the breakwater. Apparently the GPS error here is over 30 meters. Why? Don't know.

So I always study my pilot books (yes I also carry them) before entering a unfamiliar harbour. And I always double check my chart plotter against the landmarks noted in the pilot books as I sail in.

This is an interesting thread, if for no other reason then the fact that there is a lot to learn from what others do. I find that I am apparently not alone in my affection for paper, nor am I the only only one who has pilot books (despite the chartplotter having built in pilot books).

Whilst I am in perfect agreement with Andrew, I can foresee the day when "sailors" will not have paper, nor will they understand how to DR or do terrestrial or celestial navigation. Why? Because it is just like modern cars. Back when I was young (a long long time ago), most (boys) knew how to repair their car. Today, noone does, because when you open the hood (bonnet to english types) all you see is a black box with a few wires. You simply can't repair it yourself.

The same will happen with navigation. It will become so automated (and reliable) that no one will learn the "old fashioned ways". There will simply be no need to.

Eventually someone will make a video for posterity's sake featuring "old salts" like Andrew and myself, the last persons on earth who actually ever used celestial navigation in practice.
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Old 05-11-2012, 01:49   #979
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Re: Paper Charts Now Unnecessary

Fascinating thread - in many ways boring as batsh!te but in other ways very enlightening.

It is clear that some posters have no idea about either the theory or the application of navigational techniques - this is not a value judgement, just an observation. However all of them can clearly use a GPS to find their way around and most can use a chart plotter to the same end.

Me; well like most I fall somewhere in the middle, I like to use paper to navigate with, I like to use GPS for position fixing and I always prefer pilotage in close quarters. If I feel I need GPS accuracy in close quarters then I feel the quarters are too close.

I am learning to use CP's for route planning and maybe one day will make the switch to use them for navigation as well
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Old 05-11-2012, 02:17   #980
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Re: Paper Charts Now Unnecessary

Don't abandon traditional forms of navigation just because you only have electronic charts. There are many situations where traditional forms of navigation are superior.

Entering a bay with underwater hazards is the sort of time you must use both traditional and gps methods of navigation.
GPS is very accurate, but the charts are often not. One of the big advantages of many forms of traditional navigation is that displacement of the chart does not alter our position relative to hazards.

For example if the chart, unknown to us, is displaced 100m and we want to pass 100m away from a rock our perfectly accurate GPS will take us directly for a perfect collision.
If we have say a clearance bearing from from a tip of land the chart could be 50 miles out and we would still miss the rock.
Neither method will help if the rock is not shown in the correct position relative to bay, but with some simple traditional methods one major and common charting problem is eliminated.
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Old 05-11-2012, 03:24   #981
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Re: Paper Charts Now Unnecessary

Actually in the true sense it is used to estimate your position before taking a fix. Thus starting the cycle again of using dead reckoning, nothing to do with landmarks at all.

It is quite simply using your last known position to calculate your approximate position based on the last fix, (known position) and allowing for course, speed, time elapsed, estimated drift, leeway etc.
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Old 05-11-2012, 03:44   #982
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Re: Paper Charts Now Unnecessary

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Originally Posted by Ex-Calif View Post
Gotta be careful here...

The one boat induced an error with a bad fix. you cant hang that o the gps.

The guy that was using DR was more likelynusing visual navigation. DR would indicate to me he plotteed a course considering current and leeway and followed the resulting mag heading. More likely he was navigating off landmarks - visually.

And to Andrew. For me "set" includes current and wind leeway effects. How far did the boat get set down current and downwind.

I am not proposing reduce everything to numbers, just pointing out one can. You prefer to provide an educated guess on set. If I know that from past experience I get set 1 mile every 5 miles in a 15 knot reach it is simple to calculate CTS to offset the set. Add the current effect (kts X time) and you can calculate the course correction to add or subtract for set.

I encourage folks to practice this often. I see too many skipers sailing a french curve cuz they dont understand set.

Of course the gps does this for you by providing constantly updated CTS.

Technically that wasn't GPS error -- it was GIGO error -- garbage in, garbage out. Nevertheless, he was over-reliant on the GPS, and didn't plot it on a chart, or probably, even look at a chart. Other people didn't double-check the coordinates and apparently didn't look at their charts either. The error -- IMO -- was how he used the GPS -- blindly, without checking with the chart. I don't think anyone has mentioned it yet, but the "GIGO" factor is one reason to not rely completely on electronics.

We even tried to radio the other boats, but they were sure they were on course, and since our chart plotter was down, didn't take our observations (his, not mine, I was really "fresh meat" at that time) too seriously -- fo r a while.

Since I was on the boat, and I saw him take out his hand compass, take three readings and intersect them on the chart, I'm pretty sure he was using DR. Also since that was my first lesson in DR, from a highly experienced sailor. He taught celestial navigation in the navy. You really do have to know exactly where you are in the waters we were in -- there are a lot of shallow places.

Hmmm... I may have described "set" by accident but I don't actually know what you're referring to. You can do 15 knots on a reach? Wow --
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Old 05-11-2012, 03:46   #983
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Re: Paper Charts Now Unnecessary

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Originally Posted by Cookiesa View Post
I love when navigating tight channels etc is brought up and the enevitable story of a bad "gps" location causing someone to run aground.

Bet you the gps is more accurate and the position updated much quicker than anyone doing DR could do it, considering the data is the same, if the location of the reef etc is wrong or marks missing as already discussed then the odds are someone is going to come unstuck. Most sailers I know, regardless of the method of naviagtion they use do as already mentioned, ask for local knowledge, watch for tell tale signs on the water of impending danger and keep a good look out.

Very few would be marking their charts in this situation but rather concentrating on keeping the vessel safe.

Oh yeah, if you need information FAST, the chartplotter is your friend!
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Old 05-11-2012, 04:23   #984
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Quote:
Originally Posted by Andrew Troup
Dan

By "wind leeway" I wonder if you mean what I would call "wind drift". This behaves like current set, but arises from a different cause: the movement of the surface layer of water downwind.

If you genuinely mean what's conventionally called "leeway", I'm personally rather queasy about treating it as a set.

That's because the units are different.
Andrew Leeway or winddrift - meh!

The boat slips sideways and drifts downwind. I think you want to put a finer point on it and we may have different terminology.

Raku - Using a hand bearing compass to take transit readings is pilotage. It is a form of visual navigation.

And once again you can't fault gps navigation accuracy if someone enters a bad waypoint.

You also cant fault celestial navigation if someone makes a math error.
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Old 05-11-2012, 05:00   #985
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Re: Paper Charts Now Unnecessary

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Andrew Leeway or winddrift - meh!

The boat slips sideways and drifts downwind. I think you want to put a finer point on it and we may have different terminology.

Raku - Using a hand bearing compass to take transit readings is pilotage. It is a form of visual navigation.

And once again you can't fault gps navigation accuracy if someone enters a bad waypoint.

You also cant fault celestial navigation if someone makes a math error.

I acknowledged that the flaw with the chart plotter was user error -- in three ways. First, he put in bad waypoints. Second, he didn't check them. Third, he didn't confirm with a chart. I didn't fault the chart plotter; I faulted his over-use of it. I think Wolf's point about them not always being accurate is especially valid in out-of-the-way places that aren't charted well to begin with (based on what I've heard here). I've seen reports of things like atolls that weren't on any chart here on this board. But I think if the person had relied on his/her chart the same thing would have happened. I have a friend who has done extensive sailing to many places around the world, and he confirms what he has on the chart (no chart plotter) by having someone go up and sit on the spreaders and look down into the water.

The greater risk, the more caution has to be used. Going aground on coral will be a lot worse for the boat than a soft grounding on sand or mud.
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Old 05-11-2012, 05:04   #986
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Re: Paper Charts Now Unnecessary

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Originally Posted by Ex-Calif View Post
Andrew Leeway or winddrift - meh!

The boat slips sideways and drifts downwind. I think you want to put a finer point on it and we may have different terminology.

Raku - Using a hand bearing compass to take transit readings is pilotage. It is a form of visual navigation.

And once again you can't fault gps navigation accuracy if someone enters a bad waypoint.

You also cant fault celestial navigation if someone makes a math error.

PS I get your point on DR. My friend used what information he had to predict where he would be in a half an hour. Being very familiar with both his boat's traits and the waters, he was spot-on, but he did use landmarks, you're right.
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Old 05-11-2012, 05:25   #987
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Re: Paper Charts Now Unnecessary

It is my understanding that merchant ships are no longer required to carry paper but they do have several electronic systems. Is this correct? Also are pleasure boats required to carry paper by law?
Thank you all for a very enlightening thread. It has been very interesting for myself as a newbie.
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Old 05-11-2012, 05:51   #988
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Re: Paper Charts Now Unnecessary

Kiwi - well you just opened a huge can of worms. The answer is: yes, no, maybe, or if you don't like those: maybe, yes no

In Denmark, where I live. All boats (no matter how small) are required to have 2 sets of navigational tools, whereof one shall be paper charts. Period. No discussion.

Unless (there is always an unless), you have EDISS (think that is the abbreviation), which means you have two totally independent e-nav. Independent meaning everything in duplicate and double redundant, including power supply etc.


SO that's here. It is different in other countries.
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Old 05-11-2012, 06:10   #989
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Re: Paper Charts Now Unnecessary

So that would be one on boat power and a hand held with several spare batteries. Its very interesting all the different rules and almost imposible to keep up with.
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Old 05-11-2012, 06:36   #990
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Re: Paper Charts Now Unnecessary

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So that would be one on boat power and a hand held with several spare batteries. Its very interesting all the different rules and almost imposible to keep up with.

It's a little more complicated in the US. You're not required to have any kind of charts. However, maritime law applies, and there could be any number of circumstances where having a chart or plotter could have helped avoid an incident, and then conceivably they could say that one did not take "all reasonable precautions."

For instance, suppose you run aground in a storm, and a crew member or guest ends up being injured? Not having a chart, which would have helped you avoid the grounding, would probably mean that the injured party would win any lawsuit.
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