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Old 05-04-2010, 15:31   #166
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I wonder whether the skipper of this ship was using paper charts or electronic....

Stranded ship "time bomb" to Great Barrier Reef - Yahoo! News
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Old 05-04-2010, 20:44   #167
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So you don't subscribe to the theory that freighter was intentioanlly grounded on the reef, as part of a Chinese plot to destroy the Australian tourist industry?

To call this grounding an "accident" would be an insult to the finely trained Chinese offciers and crew aboard the ship. Calling it a successful act of economic sabotage, would be a great credit and compliment to them all. (Different mindset.)
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Old 05-04-2010, 20:55   #168
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There seems to be a fair amount of folks with their two feet firmly on dry land offering "6-decimal place" advice on various navigation equipment, systems, techniques. Once you are out in the oceans with pitching and rolling decks you are hard pressed to get accuracies less than +/- 5 to 10 degrees. Add in the totally forgotten fact of "leeway" due to currents or keel slippage and you are rarely "pointing" at your destination. In a sailing/power vessel we are in most cases traveling sideways more than straight ahead.
- - As to specific equipment, the degree of accuracy is almost totally determined by the experience and hands-on skill of the equipment by the operator when out in the oceans.
- - Tuning, range selection and allowance for "leeway" need to be considered in radar usage. Radar is the best device to tell you there is actually something out there around you and you need to determine what it is and exactly how it will impinge on your desired course. If you do not know how to use radar then it could be a dangerous device which lulls you into situations you should not venture into.
- - Same thing with paper charts with or without GPS and Plotters or E-nav systems. If you do not have the skill and hands-on experience navigating with any version of them, you should stick to visual, daylight situations. As others have mentioned and alluded, relying on electronics to compensate for the inability to be able to navigate can get you killed at worst and cost you your vessel at best.
- - Navigation solely by paper charts in these days of high density traffic and fast moving ships using compass - dividers - parallel rules can consume a lot of time that is needed to see and avoid other traffic or hazards. As you advance in skills of navigation you can add more "time-saving" devices such as GPS and plotters and radar and AIS, etc. to provide you with information about where you are and what is out there around you that might ruin your day.
- - I have seen / witnessed / observed the aftermath of dis-orientated masters of vessels cause the death of their children and ship-mates especially after a long or arduous time at sea. Situational awareness is about using all the devices and techniques from navigation 101 techniques to advanced electronic nav "aids." Having a nice large "picture" of where you are and what is around you when you coast-in with a fuzzy brain and bleary eyes can and does save your bacon.
- - All the basic nav techniques and additional electronic aids to navigation are only as accurate as the sailor using them. Having a 2 meter accurate nav system in the hands of a 2 km accurate sailor is not going to make him any better or safer. He needs to learn and practice and use the equipment from raw sights plotting to radar operation and fixes until he is also close to the accuracy of the equipment.
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Old 06-04-2010, 02:13   #169
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I'm certainly not an expert Radar user, so would take expert instruction; which would begin with an accurate representation of what I said.
My apologies for the slight misquote.

The rest of my message about radar bearing accuracy versus visual is still relevant.
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Old 06-04-2010, 03:32   #170
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All the basic nav techniques and additional electronic aids to navigation are only as accurate as the sailor using them. Having a 2 meter accurate nav system in the hands of a 2 km accurate sailor is not going to make him any better or safer.
Well said, and why I think the best navigators learn first principles first, and then never stop learning.
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Old 06-04-2010, 09:07   #171
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I am afraid you all are confusing bearing resolution with bearing accuracy. These are two different things. A wider horizontal angle will bring resolution (I call it target discrimination) down so that two targets that are close together will only show one echo on the screen.
However, for bearing accuracy, the width of the beam is not a factor. The factor that determines bearing accuracy is the size of the "steps" that the scanner makes while turning. A radar with a 5 degree horizontal opening angle doesn't make 5 degree "steps"... it makes multiple "steps" per degree. Even the JRC 1000 is listed as within 1 degree accurate on bearing.

If you add a compass for true bearings (and North up display if you wish), the accuracy of that compass is a factor too. Inaccurate installation or lack of calibration is not a factor because it must be installed right and calibrated. You can f&*k up any device by installing it wrong. Operator error is not a factor because you should operate it right. You can f&*k up the accuracy of any device by using it wrong.

A ships radar is indeed much more accurate on bearing than the radars for yachts. Here are some examples: Radar Basics - Accuracy of Measurement
As you can see, we're talking a fraction of a degree there and the MSSR-2000 is accurate to within 5/100 of a degree.

Also, stating that a 4kW dome is not representative for yachts (like it is bigger/better) is not right. We're talking about a small dome, not even an open array scanner. I think it is more common than smaller domes, at least it is where I am.

A radar set that doesn't have EBL (Electronic Bearing Line) is just silly... they all have that, even the JRC1000 does have it, as they all have VRM's (Variable Range Markers). You don't have to estimate the bearing on a radar screen, you use EBL.

A radar set without a heading sensor (heading up display) is actually more accurate for a radar bearing than one with a compass, because the error of the compass is left out. The problem is that the bearing is relative to the boat's heading, so for plotting you have to calculate the true bearing and that is when you add the accuracy of the compass used to the mix again. But for purposes of collision avoidance you don't need a true bearing so that a target in front of your bow really is in front of your bow and you must change course to avoid collision.

The image painted by the radar on it's screen is NOT a virtual reality. If you think that, you either don't know what virtual reality is or you don't understand what radar is. Targets on your radar screen are real things that you look at with radar vision, just as you can see them with normal vision, or IR vision. Is the image of a FLIR unit virtual reality? How about what you see when you use binoculars? or how about the sea-bed on you fish finder? None of those are virtual reality.

GPS time is the most accurate clock you will have on your boat. It is more accurate than your "atomic clock synchronized" time piece or the time signal on SSB. Every GPS satellite has an atomic clock aboard and the GPS uses up to 12 (many more soon) of those satellites, plus WAAS or DGPS correction methods to make it more accurate. The time you see is compensated for the distance between you and those atomic clocks. Your SSB time signal is not compensated at all because your transceiver doesn't know where you are and the distance and signal path between the transmitter and your radio. Same for those atomic clock synchronized time pieces. Also, those use long wave radio transmissions that introduce much more errors that the UHF space to surface transmissions from GPS satellites.

Last but not least we get to the accuracy of GPS. True, it is based on an computer model of the shape of the globe. But what you fail to realize is that so is your chart. When your chart datum is WGS-84 and your GPS is set to WGS-84, the error of that model is compensated automatically. This is really basic navigation knowledge people, come on!

cheers,
Nick.
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Old 06-04-2010, 15:35   #172
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Last but not least we get to the accuracy of GPS. True, it is based on an computer model of the shape of the globe. But what you fail to realize is that so is your chart. When your chart datum is WGS-84 and your GPS is set to WGS-84, the error of that model is compensated automatically. This is really basic navigation knowledge people, come on!
There is a lot more to GPS and chartplotter precision and accuracy than the datum of the electronic chart.
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Old 06-04-2010, 16:10   #173
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There is a lot more to GPS and chartplotter precision and accuracy than the datum of the electronic chart.
Please explain!

p.s. there's no difference between electronic and paper charts for this; both have a datum that should match the setting in the GPS.

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Old 06-04-2010, 18:25   #174
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boy is this a convoluted debate,

[QUOTE]What keeps me holding on to my paper charts is that ability to personally scan a whole detailed (large scale Harbor chart) to check; transits on peaks; bearings to points; variety of details outlined in the Pilots/Sailing Directions to make sure that the chart and Pilotage information gels with the chart.
QUOTE]

You dont get the whole point of digital charting. Firstly the whole concept is based on the existence of a digital fix. Hnce you dont need to scan the hills looking for stuff, you are ( appromately) where you are. What GPS does not tell you is whats around you or under you. Thats whats the chart is for.

Hence you dont need to match a digital chart to its surrondings, but of course you do have to treat all chart info with a degree of suspicsion.

I always laugh at pleasure sailors saying they use paper charts for all ports etc. Yes that fine if you sail into and out off the same ones all the time. IN my case I'd need hundreds of paper charts.

Quote:
There is a lot more to GPS and chartplotter precision and accuracy than the datum of the electronic chart.
I think Nick was talking in general terms. Yes there are other issues such a DOP and environmental errors etc. But these are small in comparison to charted errors.

PS Nick, As a non dutch, non UK I take exception to your comment, I have met many many UK sailors that have an RYA ticket , and are just as much a button pusher as one or two dutch yachties I have met. Having a "ticket" doesnt make a navigator. Experience does.

The fact is folks that like it or not the paper chart is on the way out, none of the hydrpgraphic offices want them. As ECDIS makes it way accross all commercial craft, It will kill the economics of paper charts. Its already very difficult to get your hands on some out of the way places even today. I like paper, but I accept the reality of technology.

The arguments about the reliability of technology are nonsense. The fact is we accept a fatality rate then is the result of technology failure, and it doesnt stop the progress or the technology or peoples reliance on it. ( and ever was it thus). Saying that GPS "might " fail so what, the sea can kill you in so many ways, GPS failure is the least of your worries.
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Old 06-04-2010, 20:37   #175
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I wouldn't say that electronic charts are going to kill paper charts, but rather they will kill commercial publication of paper charts. Those navigators who still want paper charts will have the best option of all: Buy your own wide-format printer (they're cheap in the larger scheme of things) and PRINT YOUR OWN paper backups, when and as you need them, knowing they are fully current because you just updated the electronic source for them the hour before you printed them.
Paper will never be dead, you'll just have to keep on paying $4000 per gallon for the ink to make it. (Literally.)
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Old 06-04-2010, 20:45   #176
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. . . GPS time is the most accurate clock you will have on your boat. It is more accurate than your "atomic clock synchronized" time piece or the time signal on SSB. Every GPS satellite has an atomic clock aboard and the GPS uses up to 12 (many more soon) of those satellites, plus WAAS or DGPS correction methods to make it more accurate. The time you see is compensated for the distance between you and those atomic clocks. Your SSB time signal is not compensated at all because your transceiver doesn't know where you are and the distance and signal path between the transmitter and your radio. Same for those atomic clock synchronized time pieces. Also, those use long wave radio transmissions that introduce much more errors that the UHF space to surface transmissions from GPS satellites. . . .Nick.
Actually, there is more to time than meets the eye - - Accurate time is a floating issue as there are 3 different UTC times and a couple of different AT times. GPS time is the least accurate of all the different times with errors that are constantly varying from 0.5 to 1.5 seconds from UTC time. Here is a good article from Ocean Navigator magazine about Time and its many faces and GPS time.
GPS-derived time baffles NOAA researcher | Articles & Archives | Ocean Navigator: The magazine for long-distance offshore sailing and power voyaging
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Old 06-04-2010, 23:37   #177
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[QUOTE=goboatingnow;431828]boy is this a convoluted debate,

Quote:
What keeps me holding on to my paper charts is that ability to personally scan a whole detailed (large scale Harbor chart) to check; transits on peaks; bearings to points; variety of details outlined in the Pilots/Sailing Directions to make sure that the chart and Pilotage information gels with the chart.
QUOTE]

You dont get the whole point of digital charting. Firstly the whole concept is based on the existence of a digital fix. Hnce you dont need to scan the hills looking for stuff, you are ( appromately) where you are. What GPS does not tell you is whats around you or under you. Thats whats the chart is for.

Hence you dont need to match a digital chart to its surrondings, but of course you do have to treat all chart info with a degree of suspicsion.

I always laugh at pleasure sailors saying they use paper charts for all ports etc. Yes that fine if you sail into and out off the same ones all the time. IN my case I'd need hundreds of paper charts.

To clarify goboatingnow, I treat all navigational aids and instruments with suspicion be it charts or electronic fixes or even the VRM and heading error on my radar.

That is why I am continually checking to make sure things gel and why I prefer to have full size detailed paper charts for first time approaches to give me that overview

Having done a number of circumnavigations mostly to remote places in exploration type super yachts I have witnessed many “Radar assisted collisions” and “GPS assisted Groundings” on other vessels because of watch keepers having single reliance on their favored piece of modern navigational magic.

I think this discussion (on my part) is to warn of the dangers in that type of loyalty… to those just beginning.
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Old 06-04-2010, 23:42   #178
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Actually, there is more to time than meets the eye - - Accurate time is a floating issue as there are 3 different UTC times and a couple of different AT times. GPS time is the least accurate of all the different times with errors that are constantly varying from 0.5 to 1.5 seconds from UTC time. Here is a good article from Ocean Navigator magazine about Time and its many faces and GPS time.
GPS-derived time baffles NOAA researcher | Articles & Archives | Ocean Navigator: The magazine for long-distance offshore sailing and power voyaging
Wikipedia (the ultimate source of knowledge ) has an interesting discussion of GPS clocks and about why GPS time is not the same as UTC:
Global Positioning System - Wikipedia, the free encyclopedia

Apparently, the GPS satellites have atomic clocks, but consumer GPS recievers have relatively cheap internal clocks and use some clever signal comparisons to correct the time errors. Also, it seems that "leap seconds" and other corrections are periodically added to UTC, but not to GPS time.
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Old 07-04-2010, 00:51   #179
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Apparently, the GPS satellites have atomic clocks, but consumer GPS recievers have relatively cheap internal clocks and use some clever signal comparisons to correct the time errors. Also, it seems that "leap seconds" and other corrections are periodically added to UTC, but not to GPS time.
Well.... GPS time is the technical very accurate time of the atomic clock. Stuff like leap seconds are not added to GPS time, but the total difference between GPS time and UTC is transmitted in a special message from the satellites and the software in the GPS receiver is supposed to apply that correction before read-out.

The thing is: you can extract an electrical signal from the GPS that "pulses" exactly like seconds, with atomic clock accuracy. But... the software inside the GPS can take it's time to apply the offset for UTC and display the value, declaring the display of time as a lesser priority than updating the position for example. Old GPS units were always starved for CPU power, resulting in those "up to 1.5 second" delays in updating the screen. I can't understand that the people in the article linked by OsirisSail didn't comprehend this... just the fact that the error was always resulting in a negative error and talking to some engineers from manufacturers should have told them the cause. I think they don't fully understand it.

Anyway, we have used GPS receivers 10 years ago for very accurate NTP servers on the internet (Network Time Protocol). In every case, the GPS is opened and a wire soldered to the point of where that accurate "heart-beat" is available. This is then used to synchronize a clock using a PLL lock. This results in an accuracy that would be hard to tell from an atomic clock. The avg would be the same but from second to second it might be 5 milliseconds off or so (that is 5/1000 of a second error).

Over the last years, equipment designers have been blessed with much faster CPU's that are more energy efficient than ever. This translates to accurate time, even for cheap GPS receivers with not so good software. Top models have always been good and the newest sensors like from Maretron are just awesome and even sent 10 NMEA messages per second! (meaning they are fast enough to complete all calculations at least 10 times per second.... the question is how long your plotter or display takes to put it on your screen!!)

Every GPS has a cheap clock because it can be synchronized to the GPS satellite clock using a PLL circuit, making it as accurate as the atomic clock in the satellite. The problem wasn't the hardware (other than slow CPU) but the software. Better software can do more in less time on the same CPU as bad software (like Windows slowing your PC down so much more than other OS'es).

But even when one would have one of those old GPS designs with a clock that is always 1.5 seconds slow... it would still be the best clock on board and way good enough for anything to do with navigation.

ps: do you know that the Russian GLONASS system is back in business again?! Last March 3 more satellites were launched to bring the number of satellites to 23 again with coverage for 80% of the globe with an accuracy of between 7 and 8 meters.

ciao!
Nick.
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Old 07-04-2010, 06:32   #180
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One major advantage of paper charts over electronic charts being used in a plotter or GPS integrated e-nav computer program - is - no little boat symbol tracking across the map. If you turn off your GPS feed to your e-nav computer program you have in essence, a "paper" chart on the screen. It is the placement of the "little boat" symbol over the chart that results in many unfortunate incidents.
- - It is a fact as you must acknowledge when downloading charts from NOAA and other charting organizations that the "registration" of a nautical chart so that a GPS location can be displayed most often is wrong. Or more simply said - the charts generally accurately show the land masses and underwater obstacles, but the Lat/Long registration is often different and sometimes very different from real GPS derived Lat/Long's. This is called "offset". Offset in the South Atlantic at S. Georgia Island was measured as 10 nm. In the Caribbean, depending upon the "brand" of e-chart you are using the "offset" varies from zero to 1/4 nm or more.
- - When using real paper charts you are forced to do the "registration" in your head, real time. The shapes and locations of features on the chart are integrated in your head with what you are visually seeing. You really don't care what the Lat/Long's are - what you care about is that there is a submerged rock say 10 degrees to port about 1/8 nm ahead. You see the shore features visually and then look at your paper chart and see the relative positions of features on the chart. You brain can make subconscious corrections for minor errors in the drawings of the features on the chart.
- - But with a GPS integrated e-nav computer system or GPS plotter you are presented with this little symbol of your boat and its position and you assume you are "right there" on the chart when in most cases your are not "right there" but offset somewhat.
- - Another major hazard of e-charts when using GPS integration is "over-zooming." It was proposed many years ago when e-nav systems were first introduced to physically prevent the systems from being able to be "over-zoomed." The accuracy of the different "scale" charts is lost when you over-zoom. With paper charts the only way to over-zoom is to use a very large magnifying glass.
- - If you are aware and pay attention to the limitations of e-nav/e-chart systems then these systems are fantastic as you can have a library of thousands of charts available at a mouse-click away. Also you can (on my system, I can) display simultaneously several different scale charts and have in front of you the "big-picture, the medium picture, and the close-in detailed picture" of where you are and what is around you. As you become experienced in e-nav/e-chart systems the GPS derived little boat symbol becomes a "suggestion" of where you might be as opposed to definite "I'm there, period". You then use your "mark-one" eyeballs and other aids to navigation and your own brain to derive where you actually are.
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