CHARTING ERROR Discovered By Way Of Good Advice on Transiting the Northern Alligator River/AICW Problem Stretch, Statute Mile 80
Posted by Larry | Posted on 10-08-2012
Over the weekend of 10/6/12 to 10/7/12, we received the message below from Captain Sykes DeHarrt, concerning the perennial AICW Problem Stretch at the northern mouth of the Alligator River.
Clearly, this is good advice, but as you will see, Captain Syke’s info pointed out a potential problem.
Came thru there going south 2 days ago. There is absolutely no problem at the entrance if one follows the marks. The problem area has apparently been near marker 8. If you stay half way between 7 and 8 the depth never gets below 12 feet. Go from this point straight to marker 9 and don’t do the dog leg I think a lot of chart plotters show. They have added marker 8A to help keep you away from that shoal.
After reading Captain DeHart’s welcome input, we consulted the latest edition of chart 11553, and immediately spotted marker #8A mentioned in the article above. WHAT REALLY CONCERNED US WAS THE DEPICTION OF THE INFAMOUS MAGENTA LINE SHOWN AS PASSING TO THE WEST OF #8A. BOTH THIS MARKER’S COLOR, AND CAPTAIN DEHART’S COMMENTS SUGGESTED THIS AID TO NAVIGATION SHOULD BE PASSED TO ITS EASTERLY QUARTER.
We all know that navigators CAN’T trust the magenta line, but many cruisers do follow it all too closely, so a charting error at this crucial intersection needs to be called to the immediate attention of the cruising community./
First, we sent out a special SSECN Alert on the morning of 10/8/12, asking for input from our fellow cruisers, and, in particular, confirmation that marker #8A should be passed to its EASTERLY side. By the same afternoon, we had much appreciated, plentiful evidence from multiple captains, that CHART 11553 IS INDEED IN ERROR, AND THAT ALL CRUISERS SHOULD PASS TO THE EAST OF #8A!!!! IGNORE THE DEPICTION OF THE MAGENTA LINE PASSING WEST OF #8A, ON THE CURRENT EDITION OF CHART 11553!
Read the input below, say a thanks to our fellow cruisers, and then mark your version of 11553!
Can’t sign off without noting that this is a clear case of the Cruisers’ Net model working to perfection. We hear a report, professionally research the problem by bringing the 50+ combined years of our staff’s Southeastern USA cruising experience to bear, and then ask for on-site input from fellow cruisers. The cruising community responds, and within hours, we have a solution. Pretty neat, huh!
We passed through on 9/28 and had no problems following the markers. If you stay towards the green markers 7 & 9, you should be ok with good depths around 10-12 ft. Our chart plotter had the 8A and the magenta line correctly place left [East] of 8A.
We passed there yesterday 10/7/2012 No problem if you follow the markers not the plotter Passed to the east of 8A water depth was never under 11 ft.
We passed through this area on 9/16/2012 with a 130 foot motor yacht and didn’t have any problems. We ran the channel the same way Captain DeHart did, leaving “R” 8A to starboard [#8A's EASTERN side] and had 10 feet or more all the way through. We were drawing 8 feet at the time and got a call from another large yacht behind us who was aware of our draft. He was watching us on AIS and saw that we appeared to pass the marker on the “wrong” side according to his plotter and the magenta line. After assuring him to forget the line he also ran through with the reds to his right and had plenty of water.
Captain Bill Hipple
M/Y Lady Kath
10/6/2012///Sailed to a point approximately 1nm NW of 1AR, joined with the charted magenta line approx half way to G3. Maintened the charted center (magenta line) until through the opening. Experinced nothing that was not charted, in fact we consistantly had 1-2 ft more than charted. Left the chart to proceed to the AR “Marina”.
We have a shoal draft 4′-9″ but were sailing with another boat with 5 (or more) draft. Again no issues.
If you track the magenta line and draw more than 3 feet, at low tide, you WILL ground in a number of places, North entrance to Alligator River being one.
The magenta line does NOT provide lateral information, nor indicate a channel. What it does do is indicate the body of water containing the AICW and provide the basis for the mile markers – the chart preparers measure the line to establish the mileages.
There are a number of points on the ICW where the magenta line passes the wrong side of the mark, not just by gps location, but shown on the NOAA raster charts. There is a location south of Barfoot landing where you will not be able to track the magenta line unless your boat is amphibious.
A few years ago, one of the revisions of the NOAA raster chart showing Shallotte Inlet provided some wiggles in the magenta line between marks. This would suggest the line might have tracked the channel. Not only did it not, but when we went through the marks had been moved to respond to the recently sounded shoaling pattern.
I was through the intersection of Albermarle and Alligator River on 10/12 and 10/17 with no problems. With my 5 foot draft I always had at least 7 feet under the keel by using the westerly green 3 and hugging the greens all the way through.