Thursday, October 30, 2014

Following The Magenta Line (Navigation)

Bull River, SC
32 30.450 N 080 33.838 W
 
We made it almost all the way from Charleston to Beaufort on Wednesday. Good progress. Along the way we spent a lot of time following the magenta line. That's my topic for today.
 
 
In the picture above, you can see a magenta line printed on the chart. We see the same line on our GPS. The idea is that the magenta line is the "standard" way to navigate between points A and B. Compare it to the white line down the middle of the highway.
 
If you do follow the magenta line there are benefits. First, you should avoid shoals or other dangers. If you choose your own line from A to B, then you must check every inch along that line for hazards.
 
Second, the magenta line often has compass headings and distances printed alongside the line. That information is useful.
 
But there are caveats. The magenta line is very seldom updated, and can be very much out of date. The most infamous such case we know is at the entrance to The Alligator River in NC. Shoals have shifted since that line was first drawn. If you follow the magenta line there you are guaranteed to run aground. Worse, if you follow the red/green markers (which are more authoritative and up-to-date), your charts will show that you will pass over a shoal only three feet deep! USA charts and magenta lines were only updated once every 10 years, but someone made a mistake in this case and missed the changes at the Alligator River, so that line on our charts is 20 years out-of-date. (The US government will not longer print paper charts. I presume that they will also update the electronic charts available for download in real time.)
 
A more important caveat is to use your eyes and all available information. The red/green markers and buoys are the "official" guides in most cases. However, sometimes they get knocked down or dragged to teh wrong place, so a "notice to mariners" goes out to tell us about the anomalies. Today, most cruisers have enough ways to get those corrections that we should not be surprised.
 
In rare cases, information is contradictory. Last year, we heard Coast Guard warnings on the radio about a buoy at the entrance to WInyah Bay being off station. An hour later we passed that exact spot, and the buoy in question seemed to be exactly where it should have been. ALARM! CONTRADICTION! HIGH ALERT!
 
But more dangerous and sometimes more amusing, are the cases where inexperienced boaters follow the magenta line slavishly. We were passed once by a sailboat. Five minutes later the same boat had slowed and it was getting dangerously close to us. I took evasive action, but as we passed I looked into the other boat's cockpit. I saw a woman sitting at the wheel with her nose 2 inches from the chartplotter slavishly following the magenta line without looking around. In your car you would never follow your GPS without looking out the windshield would you? Oh God, please don't tell me you do that. DON'T DO THAT!!!
 
Following The Magenta LIne in Life sounds like a very rich metaphor for another blog post for another day when I'm feeling philosophical.
 

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