Posted by Larry Dorminy | Posted on 04-20-2012
Due to persistent shoaling, in early 2011 we designated the Waterway south of McClellanville to Awendaw Creek, as an “ACW Problem Stretch.” As before, we recommend passage at mid or high tide.
And what began as a caution has turned into an excellent discussion on GPS. Read and learn!
Yesterday we traveled from Charleston to Georgetown on the ICW. At GREEN 43 we were dead on the magenta line when the depth under our props went to 0.2 feet. We draft only 39 inches so this is really a problem for most boats.
We put out a securite call on the VHF and saved a couple of boats from going aground. I later heard chatter from a couple of sailboats we had passed earlier that they were having to wait for high tide to traverse this section. It was only a bar and lasted a few seconds as we cleared it but it gave us a start. Today I heard locals in Georgetown talking about trouble in the same place. Be careful out there.
Rusty and Jan Carlisle
I too experienced the shallow water following the magenta line on my Garmin 4210 in this area. I have found that Mr Garmin has put my “boat cursor” in the marsh while in the waters of Georgia and S. Carolina. I have find deeper water by going off the magenta at slow speed usually toward the inside of turns. I poke around a bit and find the “real channel”. With all this said, I still love my Garmin electronics. Most of the time the magenta is right on.
Rick, Sun Gypsy
I think you meant the outside of the turns. General rule of thumb is stay 2/3 rds of width to the outside. Imagine the current flow scouring out a channel. The scouring velocity is greatest on the outside of the turn.Seek the side with larger vegetation and steeper banks. Of course there are many other factors that can cause variations with this “thumb” rule.
This may or may not be another example of what can happen by spending too much time following the magenta line rather than using visual observations and following the channel markers instead. Often coming up and down the waterway, we found our plotter showing us crossing land instead of being in the channel. We have transited this section many time and were told by other boats over the VHF that there was shallow water, one telling us they
found 4 feet in the channel. When we crossed we actually found 8 feet of water in the channel some five minutes after they passed through. There are other areas like Cumberland Dividings where following the chartplotter will put you solidly aground. I’m not saying this is the case here, but would caution everyone to not depend on the plotter for more than a reference and use good old fashion navigation. When I hear any reports that the boat was aground and on the magenta line, I have to ask myself how accurate the plotter is in this section. Many boats will make the same mistake and before long there are several reports of groundings because too many of us religiously follow the magenta line. The towing companies will often tell us that they have pulled many boats off shallows in the area. The reason is because following the plotter into shallow water is a common problem. We often see many boats running from green to the next red marker down a channel instead of staying well in between the markers. Many channel markers along the ICW sit in one or two feet of water, but boaters will think that as long as they are inside the markers the channel is deep. Running up close to them will almost always lead to a grounding. Since our first trip south on the ICW in 1993 we have observed so many boats hard aground in what they thought was the channel, while we passed safely by. The depths do change for a variety of reasons and caution is always needed, especially in known problem spots. We too follow the various websites looking for the latest information, but often find reports that are based on operator inattention more than poor conditions. Some channels are less forgiving than others should one stray too far.
The problem isn’t with the chart plotter, it’s the map they used. The GPS is telling you exactly where you are, but the channel has moved relative to the chart that is published that was used on the chart plotter. The magenta line is published on the chart, and so if the channel has been moved by the moving water, which it has, then the magenta line will lead you astray.
Follow the channel, NOT THE MAGENTA LINE! Makes no difference how new your chart plotter is, it has to do with when the chart used was updated. When you update your chart plotter, hopefully they have used the latest charts available.
Chuck Gorgen aboard ODYSSEE