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Old 16-03-2009, 04:45   #151
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Originally Posted by meyermm View Post
Does the fact that I have stated that the Moorings charts are supposed to be more accurate than the official charts not say that they are all unreliable paper or electronic if based on paper charts?
If you read my post you will see that I was not addressing that at all. I quoted and addressed the following question that you asked of us all -
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Originally Posted by meyermm View Post
While I am sure US electronic charts are very accurate would you be as confident say in Tonga.
I take it that the factual answer to your question was not as supportive of your case as you thought it would be?
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Old 16-03-2009, 05:31   #152
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This has been a really good discussion. Good questions and good answers. It would be even better if the egos were left out of it.

Let's put aside the bickering, and stick to the navigating. Please!
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Old 16-03-2009, 07:09   #153
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Wow! I never realized there ever was such a GPS vs. Paper Chart competition.

Here is my way of looking at it:

For me, travelling a lifetime in remote places they serve 2 different purposes that can better be said to complement one another rather than supplement each other.

Simply put, the value of a GPS reading is to tell people with another GPS how to find you. It does not independently confirm where you are in relation to dangers, but offers very accurate repeatability to allow you to return to a given spot.

A Paper Chart (or an electronic chart based on paper datum) gives you a professional drawing of land masses using ranges and bearings together with historical observations of hidden dangers and soundings. This is overlaid onto a lat/long grid that may or may not be accurate. But the prudent mariner assumes that it is not!

What the prudent mariner does is to use radar ranges and bearings together with parallel indexing techniques and a confirming eye on the depth sounder to keep his vessel a safe distance away from charted dangers when he is coasting a planned route (day or night).

You can use paper and/or electronic charts to measure and lay off those safe coasting routes, but I prefer to always have a hard copy already boldly marked up and prepared on a paper chart so that I am not relying 100% on an electronic chart and computer.

If the GPS “own ship” position happens to agree with the radar range and bearing of a good radar target then that is great and they complement each other to give you a higher degree of certainty.

But the GPS reading is not necessary and should never be solely used to confirm your distance from a charted danger!
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Old 16-03-2009, 07:26   #154
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I will use charts from a chartering company or cruising guide author in a flash if they are said to be more accurate. But I would not trust them better than the official charts from local authority or British Admiralty etc.

The reason is that all of the official charts are actually pretty accurate with only one exception: the lat/long calibration. If they didn't have GPS when they made the chart, the lat/long is as precise as they could manage using sextant etc. This means that the coordinates can be offset from the real (GPS) coordinates.
Once the lat/long offset is determined, these charts are pretty accurate.

When you use paper charts in that situation, you have to manually offset/correct every position; I have never seen a GPS unit that can have an offset programmed in (only the datum). However, if you have an electronic plotter, the chances that you can enter the offset value are much higher and this is one of the features I demand in such a system.

Next step up is radar overlay on the chart. You can fire up the radar and adjust the lat/long offset until the chart matches.

There's also an in-between solution: those devices (forgot the name/brand) that you move over a paper chart after initializing on 2 or 3 chart positions. These can handle an offset too.

I too, find that many cruisers that never used a chart plotter, come up with reasons for not doing so that are not valid. I can only suggest to them to install some software and charts on a laptop and try it out. But remember that these systems only become useful when you can actually use them while sailing and a laptop on your knees is far away from that!

Also, most of us sail short handed. When there's just the couple sailing the boat to an unfamiliar coast, a chartplotter greatly reduces the stress and increases the safety because it allows more time for the other tasks required.

cheers,
Nick.
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Old 16-03-2009, 07:50   #155
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My approach to this tangle so far:

1. The first task of a navigator is to know the boat's position at all times. There are many ways to do this, using all available information. A good navigator can use all sources of information -- electronic, paper and manual -- when and where necessary.
2. Map = representation of locations in paper or digital (electronic) format.
3. Chart = electronic or paper map used for navigation.
4. Nautical chart = electronic or paper chart officially approved by a national hydrographic office (NOAA, CHS, British Admiralty, etc) for marine navigation.
5. Marine chart = electronic or paper chart not officially approved by a national hydrographic office. Most proprietary paper or electronic chart products are in this category. They are generally good, and sometimes provide supplementary information for pleasurecraft operators not found on nautical charts, but they are not official charts containing the information thought by national hydrographic offices to be necessary for safe navigation.
6. ECDIS = a system for displaying electronic charts and conducting marine navigation that meets internationally agreed standards. Average pleasurecraft cannot carry fully compliant ECIDS.
7. ECS = Electronic Charting System, a system for electronic charting that does not meet ECDIS standards. Most pleasurecraft electronic charting systems fall into this category. Standards are being developed for ECS by somebody. In the absence of internationally accepted ECS standards, pleasurecraft operators need to approach electronic charting products with their heads up.
8. ENC = electronic navigational chart = officially approved vector nautical charts required for ECDIS, but can also be displayed in an ECS. Most proprietary GPS charts are vector charts, but not officially approved by national hydrographic offices, so I would not call them "ENC".
9. RNC = raster navigational chart = officially approved raster nautical charts that can be used in an ECDIS if ENC are not produced for the area, and can be used in ECS (usually a laptop since it is unusual for proprietary chartplotters to capable of displaying raster charts).
10. No chart precisely and accurately displays the real world, but most charts usually are close enough. Usually, not always.
11. All navigators must have a backup navigation system should the primary system fail. Paper charts fulfill that role for GPS, should the control or satellite segment fail, or should the user segment or electronic charts fail in a way that cannot be fixed by booting up a spare GPS receiver. These failures are not uncommon among cruisers (I have a number of sobering anecdotes).
12. A good pleasurecraft navigator knows both manual and electronic navigation procedures.
13. Sound marine navigation practice includes planning (including laying out and verifying waypoints and routes, gathering and consulting official and unofficial sources of information, gathering and verifying appropriate charts and publications, gathering and checking appropriate navigation instruments and tools) and navigating under way (including using appropriate navigation procedures to know the position of the boat at all times).
14. I imagine a pleasurecraft navigator would be in the most defensible position if they could demonstrate they had acquired appropriate knowledge, judgement and skills, had conducted appropriate planning prior to departure using nautical charts and other official and unofficial sources of information, were using marine charts while navigating under way, could demonstrate those marine charts provided all the information they needed to safely navigate (were equal to the nautical charts for the area), could demonstrate they were using appropriate navigation procedures for the situation, and could demonstrate they had access to appropriate backup navigation in the event of a failure in the boat's primary navigation system. (I am not a laywer, just a boater.)
15. The older I get, the smarter the old navigators get. I have plenty of respect for lessons learned by previous generations of navigators. Old ways are not always irrelevant.

Your mileage may vary.
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Old 16-03-2009, 08:59   #156
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Originally Posted by s/v Jedi View Post
all of the official charts are actually pretty accurate with only one exception: the lat/long calibration.
Hi Nick, I think we all agree with what you said above.

Surveys of coastal dangers were done in the old days using Horizontal Sextant Angles from small boats that gave bearings from datum points ashore then later as technology improved resurveyed using Radar Range and electronic bearings to some pretty amazing accuracy.

I am fortunate to use some wonderful state of the art commercial electronic charting systems and IMO sized Radars running Superyachts.

We still don’t get sufficient worldwide vector coverage yet to rely on Admiralty AVCS so primarily use ARCS on the bridge and other systems on my laptop for planning. I love using them and actually design a “navigational channel” to be distributed on all the TV’s for the guest’s enjoyment and to keep me informed from my office or cabin.

Where I differ from you is that I believe applying offsets to the plotter encourages the watch keeper to rely more on a GPS driven position rather than continually confirming their distance from a charted danger using range and bearings from good radar targets.

Perhaps it is because I am the Master and have 3 watch keeping officers to worry about that I enforce this KISS principal of independent radar confirmation as one of my standing orders. Otherwise I would have nightmares about an officer rebooting the charting system and forgetting to apply his offsets to the plotter and providing us with a GPS “assisted” grounding.

Personally I love it when our electronic charted position goes overland and the watch keeper ignores it and expertly guides us into a small anchorage at night using parallel indexing methods and floating radar EBL’s to then say “let go Anchor” on that sweet spot.

It is a reminder to all of the weakness of depending solely on GPS and I feel they have mastered blind pilotage techniques which will stand them in good stead and let me sleep more peacefully.
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Old 16-03-2009, 10:06   #157
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Where I differ from you is that I believe applying offsets to the plotter encourages the watch keeper to rely more on a GPS driven position rather than continually confirming their distance from a charted danger using range and bearings from good radar targets.
We don't differ, I agree with you but just use a different technique that's easier for short handed sailing: overlaying the radar image on the chart. Now you have the chart plus the real-world position of it on the same display. After applying the offset, the images align more or less with always that radar overlay confirming what you see, making it easier and quicker for the short handed boat, without compromising the safety offered by real-world observation (=radar).

If you are not short handed, you don't need this.

cheers,
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Old 16-03-2009, 10:10   #158
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Quote:
Originally Posted by s/v Jedi View Post
We don't differ, I agree with you but just use a different technique that's easier for short handed sailing: overlaying the radar image on the chart. Now you have the chart plus the real-world position of it on the same display. After applying the offset, the images align more or less with always that radar overlay confirming what you see, making it easier and quicker for the short handed boat, without compromising the safety offered by real-world observation (=radar).

If you are not short handed, you don't need this.

cheers,
Nick.
Just bea really really careful to make sure that whoever installed the RADAR got the bearing and range adjustments right, or the RADAR image could be off.
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Old 16-03-2009, 10:27   #159
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Just bea really really careful to make sure that whoever installed the RADAR got the bearing and range adjustments right, or the RADAR image could be off.
Hmm, that task is too complex for most installers as they are no navigators. It's best to do that (or at least check it) yourself, maybe even using a paper chart ;-) The procedure is very easy for every navigator.

cheers,
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Old 16-03-2009, 11:34   #160
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Quote:
Originally Posted by Hampus View Post
Just bea really really careful to make sure that whoever installed the RADAR got the bearing and range adjustments right, or the RADAR image could be off.

Hmm, that task is too complex for most installers as they are no navigators. It's best to do that (or at least check it) yourself, maybe even using a paper chart ;-) The procedure is very easy for every navigator.

cheers,
Nick.
Gee I hope you guys are not under the impression that radar range and azimuth errors are fixed. A single radar range and bearing does not provide an accurate fix - it should be considered an EP.
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Old 16-03-2009, 11:42   #161
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11. All navigators must have a backup navigation system should the primary system fail. Paper charts fulfill that role for GPS, should the control or satellite segment fail, or should the user segment or electronic charts fail in a way that cannot be fixed by booting up a spare GPS receiver. These failures are not uncommon among cruisers (I have a number of sobering anecdotes).
While I generally agree with what you've written - this point is comparing apples to oranges. GPS is a position-indicating system - a sextant could be considered a back-up to GPS. Paper charts could be back-up for e-charts. Your points bring up another question - how many who use paper only have a back-up? What do they use?
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Old 16-03-2009, 12:02   #162
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Well not directly, only if they have physical access to your GPS receiver and it had track logging enabled. A GPS receiver is just that - a receiver, not a transmitter - the satellites not only don't know where you are, they have no idea you exist.
That's what the Govt wants folk to beleive .....actually in the case I mentioned it wasn't so much spy in the sky, simply a case of checking the track on the chartplotter. If I recall the impact was not recorded on the plotter with a "SPLAT!!" - but nonetheless pretty evident what had happened by the course to the mark and also the time / course then spent near the bouy. ........and the absence of anything else he could have hit on his track - 4 foot in the air whilst planing

Alledgedly he was "otherwise engaged" keeping the Admiral happy down below .......but that may not be strictly true as we do like a good gossip in these parts and always willing to make a dull story more interesting
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Old 16-03-2009, 12:04   #163
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Surveys of coastal dangers were done in the old days using Horizontal Sextant Angles from small boats that gave bearings from datum points ashore then later as technology improved resurveyed using Radar Range and electronic bearings to some pretty amazing accuracy.
I'm not a surveyor, so am prepared to be edified, but I'm not of the belief that radar and EBLs would be sufficient for surveying. I believe that surveying has kept up with the times, but the old tried and true methods (ie with a theodolite) are still very much in use; in addition to methods using GPS as well as aerial/satellite imagery.
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Old 16-03-2009, 12:29   #164
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Hmm, that task is too complex for most installers as they are no navigators. It's best to do that (or at least check it) yourself, maybe even using a paper chart ;-) The procedure is very easy for every navigator.

cheers,
Nick.
Which is exactly why I pointed out the importance of making sure :P

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Old 16-03-2009, 16:41   #165
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Just a couple of things regarding matters mentioned -

Regarding the difference between ECDIS and ECS (Electronic Charting Systems) as several have correctly defined. A number of ECSs are non certified renditions of the same company's ECDIS and things which may not be needed on smaller vessels are made as options rather than mandatory eg AIS overlay. These are usually aimed particularly at the small commercial user that has no need for nor the supporting systems for ECDIS, but are also aimed at the pleasure market.

I have not done a recent search as to what is currently on the market so won't get into naming products (mine is one though) but this may be something to keep in mind if looking for an ECS to depend on for navigation on a PC.

Regarding radar as a nav aid - I support Lodesman's comments on this. Especially so as one needs to have at least an 1.5 metre array antenna to start getting results which start being sensible, especially in azimuth and even then there are a limited number of things which one can get an accurate range against due to curvature hiding the lower parts of features and the need for them to have been accurately charted (daymarks and some lights often being ok examples).

Regarding electronic nav tracks being used by authorities after an accident or incident as mentioned by David_Old_Jersey - Many ECSs will maintain an undefeatable electronic log of all inputs eg ex GPS, log, compass, depth, water temperature, and whatever as well as system alerts and alarms (eg you have approached - alert - or entered water shallower - critical alarm - than the safety depth contour that the navigator has set in the ECS). In my own case this means every input is recorded about once per second eg GPS position data, SOG, COG, satellite status, etc is logged on average every second, as is every other input such as compass, wind, depth, etc. The navigator can also add his own notes of any kind as well and can review the log sorting on whatever he is most interested in eg on NMEA inputs, his own notes, alarms, etc.

These logs will be used in the investigation of an incident or accident and while the production of these logs is usually undefeatable one can, of course delete them afterwards. But one would, of course, be on an immediate back foot if it was found that after an incident or accident one had done so. Also, as the data is recorded second by second and not smoothed by averaging as the displayed track will be, it will give the fine detail of position, speed, course changes, etc at the point of the incident or accident.

A number of times over the years I have preserved these logs after events just in case the other party reported them as incidents/accidents (eg once I was side swiped while I was at anchor by a small commercial vessel drifting with its skipper asleep, fortunately with only very minor damage).
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