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Thursday, February 14, 2013

How To Read a Nautical Chart

How To Read a Nautical Chart

Boating often comes as if from another language - perhaps descended from German, maybe from the Romance languages.  On second thought, probably from the Scandinavian countries from which we get most of our cruise ship captains!

In any case, there are few resources (and even fewer good ones) out there for learning how to read a nautical chart.  If you're going to embark on this task, first read this: DO NOT GO BOATING UNLESS YOU KNOW HOW TO READ A NAUTICAL CHART.  Charts are your roadmap to where you're going - except there aren't any pretty roads with neat little lines on them, and there's less of a chance of drowning if you mess up.

Let's begin with this simple image from NOAA:

In no particular order, here are some things you might want to know right off the bat:

1. White water is what you want to boat within.  White means it's deep, and white varies in exact depth by the size and type of the map you're looking at.

2. Blue is water you want to avoid (then why do they call long ocean passages 'blue water' journeys?  No idea, but avoid blue because it's more shallow).

3. Red Right Return.  Know this, repeat it in your sleep, and know whether you're returning or not!  This means keep red buoys on your right (starboard) side when returning from a larger body of water to a smaller one.  In this case, going from LI Sound to CT River, Red will be on our Starboard side.

4. Anything that says 'Channel' is generally good for you and your boat, unless it says 'Restricted.'  In this case, the Saybrook Outer Bar Channel can be navigated between two rock jettys (denoted by black dashed lines).

5. The numbers on the blue/white contours are depths, generally by feet, although each chart has a different key indicating the depth reading (fathoms, meters, etc).

6. Lines are contour lines - that is roughly what the sea bed beneath you looks like in a rudimentary kind of way.

7. Green/Yellow is land - don't boat here.

8. Dotted lines in misshapen circles mark hazards to navigation - rocks, pilings, and other things your stern-drive and insurance company hate with a fiery passion.  For instance, you can see Griswold Piers in this example with a nice rock just SE of it.

9. Letters on the blue/white contours denote what the bottom is made up of.  It could be S=Sand, Rks=Rocks, M=Mud, or a variety of mixtures and textures.  In this case there are a few 'h' letters strewn about, which indicates a hard bottom.  Anchoring here would most likely be difficult!

10. Lights and other markers.  This is tough.  There are MANY different kinds of markers which make noise, light up, and otherwise twinkle in the night like bug zappers.  In this case, we can see at the bottom of the Channel 'Saybrook Breakwater Light' which Flashes Green (fl G) every 6 seconds (6s) at 58ft tall and visible up to 14 Miles (14M) with a horn.  Ya.  I know.

Now let's get a little more complicated.

11. With this map, further up the river, we have many more fun things that may sink our boat.  Notice first the Obstns (Obstructions = not good for boats).  There are two bridges here - one that is fixed (upper yellow crossing bar, no break) and one that raises or swings (lower yellow crossing bar, break).  Actually, it tells you to the right that's it's a bascule (raising) brige, with a horizontal clearance of 139 ft, and a vertical clearance (when lowered) of only 19ft.  

12. Also notice the Cable Area in magenta, which is a scary line that really just means don't anchor here or else you'll puncture something valuable.

13. There are also a variety of other fun marks like pilings, visible marinas (black lines that look like docks) and Lord of the Rings: The Two Towers (just kidding) between which extend power cables.  How do I know? It says OVHD PWR CAB (overhead power cable) with a clearance of 108 ft.

14. WAIT!  Don't waterways rise and fall with the tides?  How does a fixed bridge maintain a solid clearance level?  Well, it doesn't - these numbers are generally taken at mean high water (above average tide level) but again, CONSULT YOUR CHART KEY FOR FURTHER CLARIFICATION.  This is one piece of info you don't want to get wrong.

This is by no means a comprehensive list of chart symbols; rather, it's an overview that will give you a good basis to get started.  

There are tons and tons of symbols for everything from different markers and buoys to different land masses and topography.  Learning to read a nautical chart is invaluable - to that end, here are two very intensive resources that you should read cover to cover, again and again, to become an expert on this subject:

All about chart reading: http://powerboat.about.com/od/boatingnavigation/ss/readachart1.htm#

All about chart symbols::
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