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Old 09-12-2007, 23:46   #1
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How do I know if the chart is wrong?

I am reading my new copy of Octobers ( ) Yachting World mag and theres an article about some singlehander called Landles (Ho ho ho!) running up the butt of one of our more famous reefs.

Online story here from London Times
The mag article importnat bit:

"Mr Landles had run aground after relying on a marine navigation chart that gave a false position for Elizabeth Reef. ďHe had two charts, one of which was accurate and the other which wasnít. Unfortunately he was relying on the chart that was wrong."

Neither Yachting World, nor The Times help us out with what the CORRECT Lat Lon is!

Garmin World Map and Raytech World map don't have it or nearby Middleton Reef - presumably because 38 shipwrecks isn't enough

I don't have the regional charts for either etc.
About the only thing I have is Google earth which shows it 1 mile from the lat lon on some internet site, but worse is Ocean Dots which has it neatly 270 NM's north!

No wonder 38 boats have found it!

This brings me to my question:

If we hear that a charted position is wrong how do we check it?

How much offing do you keep in the Pacific using modern digital charts?

Mark
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Old 10-12-2007, 00:51   #2
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Apparently several of the electronic chart manufacturers do not necessarily put all the reefs etc on them, I have contacted Navionics re puting Minerva reef on their chart but so far havn't had any success.
All electronic charts are taken of paper charts in the first place.
So when Capt Cook charted an island all those years ago a couple of miles out wasn't a problem, now with the GPS co-ordinates being so accurate the Island / reef appears where it shouldn't be and things go bump in the night.
Nothing beats your number one eyeball when you are closing a shoreline.
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Old 10-12-2007, 01:03   #3
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If we hear that a charted position is wrong how do we check it?

How much offing do you keep in the Pacific using modern digital charts?

After you find the error and fix your keel, you post it on all the sites like this and ask a lot of questions about where you are cruising or you approach dead slow with a good sonar system. LOL
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Old 10-12-2007, 01:04   #4
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cmap is the most accurate charts for the South Pacific - saying that they don't have everything on their charts either. Get the pilots out and start reading I think.
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Old 10-12-2007, 01:23   #5
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It's best to consider everything suspect and not to try making landfall at night. Also a lot of the so called plotted currents are not accurate. I always remember the "Rose Noelle" that ended up being wrecked on Great Barrier Island. After turning turtle not far out from Wellington, they drifted for months. All the "EXPERTS" said that couldn't possibly have happened as the currents didn't go that way.
I have watched a skipper so absorbed in his GPS screen that he didn't realise that he only just and I mean only just missed a rock that the GPS told him he was well clear off.
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Old 10-12-2007, 01:39   #6
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A lot of the south Pacific charts were drawn by Capt Cook using a sextant and chronometer. It's a tribute to him that they are as accurate as they are. Not being a militarily important area, no navies can be bothered doing a more accurate survey.

It always pays to use GPS and chartplotter information with caution.
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Old 11-12-2007, 09:54   #7
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I'm sorry but that guy is an idiot....period.

I have been to both Elizabeth and Middleton Reefs. Either this guy was blind, stupid or just totally unaware that these reefs were there.

Elizabeth Reef has a very small anchorage but the reef opening is clear from the deck of a small boat in light conditions and should never be attempted in fowl weather as there will be breakers across the entrance, no matter the wind direction. No sailor should come within 3 miles of either of these places without keeping a very diligent watch. The seas break on the reef, all the way around on Elizabeth, even in the calmest weather and can be seen from about 2 miles, easily. The only way that you could run up on these reefs is if your were asleep or totally missed seeing them on your chart (easy enough to do, hundreds of vessels have done it, including commercial ships)

My 1st time there ('87), there was about 20kts of breeze and the entrance was impossible to navigate due to strong current and breakers across the entrance. In '96 I motored into Elizabeth on a clam day. It was clear that a yacht could get in very big trouble in there. There would be barely enough room for 1 vessel, in 20' of water, with 10:1 scope. Even then, there are so many coral heads in there that a wind shift may put the vessel in peril during a wind shift. It would also be dangerous to impossible to get out, if conditions deteriorated. That place is a death trap IMO.

I sailed up to Middleton Reef on both occasions. There is a great anchorage there with plenty of swinging room for 4-5 vessels. The sandy area is free of coral heads and protected from all winds (well, really seas & swell)) except NW. If a NW came up (which is extremely rare there) it is easy to get out. I stayed for 10 days on each visit and experienced winds of 30+kts while at anchor. The holding is extremly good and the anchorage is in 15-20' (all sand), well protected from swell. It never got uncomfortable there. I would highly recommend Middleton. It is the best diving, snorkeling and fishing that I have seen in the world.

Both reefs lie exacly 1/4 mile SW from their charted position. I reported that to British Admarilty in '96 (as has the charter fishing captain that comes up from Lorde Howle Island).

BTW there are over 300 ship wrecks on Middleton Reef alone. I'm not sure where the 38 number came from.
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Old 11-12-2007, 12:25   #8
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Either this guy was blind, stupid or just totally unaware that these reefs were there.
Don't beat around the bush, just come out and tell us how you feel. LOL
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Old 11-12-2007, 12:43   #9
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BTW there are over 300 ship wrecks on Middleton Reef alone. I'm not sure where the 38 number came from.
Looking at Google Earth (Maybe Google can take over Nav charting?) They are exactly on the rhumb line for both Noumea and Fiji to Sydney; Noumea to Melbourne; Northern tip of New calidonea and Tasmania; Brisbane to tip of North Island, New Zealand; Wellington and south tip of South Island NZ to the outter edge of the Great Barrier Reef. So all in all its an exact cross roads for quite a few voyages!

38 wrecks is suggested by this site and was mentioned in the newspaper article as we well know journalists can't be wrong!

I'd love to stop off at Middleton!
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Old 11-12-2007, 12:57   #10
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Here is Elizabeth Reef. The only place that you can access to anchor is just inside the break in the reef on the NE side. It is exteremely small and cluttered.


Here is Middleton Reef. The anchorage is just around the Western hook in the reef on the N side. It is very well protected, large and easy to get out of.

I need to correct one thing. It is open to NE (not NW). The tradewinds come from the SW 90% of the time.


Notice the breakers all the way around Elizabeth Reef. It is always like that, even in calm weather. The Reef is prfectly round and the swell wraps all the way around.
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Old 11-12-2007, 14:49   #11
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Mark,
GPS chartplotters are a great advance over paper charts plus hand-plotting and enable you to sail safely in situations that would have involved considerable risk using previous technology. The catch is of course the accuracy of the chart. When approaching an unknown area for the first time in reduced visibility conditions, we match the radar image of the land / navigation markers etc. to the chart. Using the chartplotter cursor in daylight, you can get an instantaneous magnetic bearing to key navigation features such as headlands, peaks, lighthouses and the like. A quick check with a hand compass, or more conveniently with a pair of binoculars with a built in compass, will tell you quickly if your electronic chart is correct or not. Not to be forgotten is to match the measured water depth to the tide corrected depth from your chartplotter.
As you approach your destination even closer, you can check the position of fairway markers as you pass them, bearing in mind of course that these are easily moved. Once you have established a confidence level with a particular area, then you can begin to rely more on the chartplotter picture.

No radar? Then you donít trust the chart - paper or electronic - until eye-ball confirmation conditions exist.
Ed
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Old 11-12-2007, 14:57   #12
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. Once you have established a confidence level with a particular area, then you can begin to rely more on the chartplotter picture.


Ed
Hi Ed, thanks for the good advice

Mark
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Old 11-12-2007, 15:01   #13
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Check the chart datum as well. Google Earth is in WGS-84, as it should be. Some older charts use different datum. Plus the surveyors may have had the wrong position from the very beginning. Think about how surveys in remote locations like this were originally done...the base line was established by celestial navigation using hopefully very accurate clocks...and if one was lucky, LORAN or Omega as early as 1968. It was not until SatNav that one could get down to the accuracy of 10 meters or so. If GPS is allowed to do a 24 hour average from a unit set in a fixed place, the accuracy can get down to a few centimeters.

If you suspect a position is wrong then check Google Earth, obviously before going.
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Old 11-12-2007, 16:02   #14
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Those pictures are so awesome - worth the price of admission alone.
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Old 11-12-2007, 16:50   #15
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Mark,
GPS chartplotters are a great advance over paper charts plus hand-plotting and enable you to sail safely in situations that would have involved considerable risk using previous technology. The catch is of course the accuracy of the chart. When approaching an unknown area for the first time in reduced visibility conditions, we match the radar image of the land / navigation markers etc. to the chart. Using the chartplotter cursor in daylight, you can get an instantaneous magnetic bearing to key navigation features such as headlands, peaks, lighthouses and the like. A quick check with a hand compass, or more conveniently with a pair of binoculars with a built in compass, will tell you quickly if your electronic chart is correct or not. Not to be forgotten is to match the measured water depth to the tide corrected depth from your chartplotter.
As you approach your destination even closer, you can check the position of fairway markers as you pass them, bearing in mind of course that these are easily moved. Once you have established a confidence level with a particular area, then you can begin to rely more on the chartplotter picture.

No radar? Then you don’t trust the chart - paper or electronic - until eye-ball confirmation conditions exist.
Ed
I personally think that chart plotters are robbing sailors of the rewarding skill of doing your own plotting by hand. IMHO, there is no better way to have confidence in your ability to find your own exact position.

When sailing around the world, the cost of new paper charts can be pretty daunting. On many occassions, I would take someone's chart in, photocopy it and piece it together. In complicated areas like Tonga and the Yasaua Group in Fiji, I would take color pensils and color in the water depths and land area by hand with my own color code. By the time I went into a particular area, I would know it intimately.

I would be very conserned about getting to some secluded area with no paper charts and have some electronic device fail on me, either through a failure in hardware (in a salt water environment) or some software glitch.

Also, God gave us eyes for a reason. More sailors need to know how to use those also. If your chartplotter says that there should not be a rock there and there is a rock there, I'd believe my eyes every time.
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