The Magenta Line


For the non-cruiser readers, this post may shed some light on how we find our way. For the cruisers reading, this post could be a rant. Here goes…

The charts that cover the AICW have what’s commonly referred to as “the magenta line”. Hang around cruisers who spend time in “the ditch” and you’ll frequently hear reference made to this feature of the charts. The magenta line is the indication of the AICW (Atlantic IntraCoastal Waterway) route. It shows the route of the ICW,  presumptively the best route.  It is the paper representation of the ICW as it winds its way south from Mile Marker -0.0- in Norfolk, down to Miami and beyond. There are other portions of the ICW that make their way along the Gulf Coast and complete portions of the Great Loop, the circumnavigation by water of the eastern half of the United States. But without some sort of guideline, it would be nearly impossible to know where the next turn is on the often convoluted route that is the ICW. The line, along with the ICW markers, or aids to navigation compliment one another in guiding the boater along this thousand-plus mile waterway.

The Magenta Line appears on all the AICW charts, and a popular assumption, particularly among boaters new to cruising and the ICW, is that if you follow the magenta line, you’ll be following the “official” and therefore, the approved route and all will be well; no misfortune could befall a prudent skipper who carefully follows the magenta line. We all know the rule about assumptions! The magenta line is a guide, and carries no magical power that transcends prudent seamanship.  The magenta line is a guide, folks. If you zero your chartplotter in on the line with the expectation of trouble-free cruising, you’re gonna have some trouble. Guaranteed! There are numerous reports on the ActiveCaptain website and notes on the ActiveCaptain interactive chart notes regarding the magenta line being wrongly placed, placed in shoal waters, not accurate, and the list goes on- some of the notes are the product of older charts that are out of date, more recent charts that are simply inaccurate, or other errors or misinterpretation. Whatever the reason, the final decision on where one goes involves more than a single line on a chart.

In addition to the charts, the ICW is marked with its own specially designated set of aids to navigation (ATON). The aids look like any other typical US aids, with the addition of a small yellow mark placed on the aid. The yellow reflective mark is in the form of a square or triangle. The triangular marks indicate that the marker is inland, or passed to starboard proceeding from north to south. The square indicates that the marker is to seaward, or passed to port proceeding north to south.  Conventional ATON’s are ordered based on an approach from seaward; with red even numbers to starboard (Red-right-returning from seaward), green odd numbers to port, and numbers increasing from the starting point: an ocean bouy, branch from a main channel or fork in a channel. ICW ATON’s can also share the ATON’s for local waters, often creating a great deal of confusion in the process!  There are sections of the waterways where the colors and number sequences are reversed as a result of the shared/dual function ATON’s (as pictured above on left and right). Normally, one would see square yellow markers on green ATON’s, passed to port north to south;  triangular on RED, passed to starboard north to south,  but there are sections of ICW where the green markers are passed to starboard, red markers to port. One must pay particular attention to the charts and the ATON numbers to insure that they pass the marker on the correct side. Yes, it makes a difference! It’s called the ditch for a reason!

The prudent helmsman will consider a variety of factors in navigation, including charted information, local knowledge, experience, the physical aids to navigation and the all important depth sounder and other instrumentation on board the vessel.  ATON’s are frequently relocated by local USCG stations to mark the best water or warn of encroaching shoal water. If a certain section of the chart and the physical markers don’t coincide, the best bet is to favor the physical markers. The skipper who blindly follows the magenta line to the exclusion of other input will soon find himself in trouble.  The nature of the waterways is that they are constantly changing, and we simply can’t see those changes. That’s the challenge of boating! So for those who are cruisers, or perhaps potential cruisers, a few suggestions:

  • Keep current charts, make notes on paper charts, or utilize previous tracks on electronic charts to add another source of information.
  • Review/study the next day’s intended route and research the problem areas on ActiveCaptain, CruisersNet, or other sources of information regarding problem areas.
  • Consider recommendations from other cruisers in negotiating problem areas, while keeping in mind that YOU are responsible for your own vessel. It’s information, use it prudently!
  • If something is confusing or doesn’t make sense, slow down!! Keep an eye on the depth sounder!  Bumping the bottom at idle speed probably won’t create a huge problem, grounding at cruise speed can make for a really bad day!

So for the non-cruisers, you may have gained a little more understanding of what’s involved in making our way along “the ditch” and how the road signs on the waterways are part of a unique system of waterborne roadways with no lines! For the cruisers and potential cruisers, a reminder to keep sharp, pay attention to all sources, and travel safe!


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