They look a lot like maps, but they’re bigger: giant sheets of paper.
And they have a bunch of tiny numbers and symbols and colors on them.
They show the coast as a mix of odd colors, and lots of tiny numbers in the water.
Welcome to the world of a nautical chart.
Obviously, nautical charts were designed for mariners—mostly big ships—to find themselves safely to and from port.
But even if you don’t own a sailboat, there are a lot of reasons to know what all those symbols mean.
And you can make your trip to the coast even more fun.
Solve the Puzzle
The first step to figuring out the puzzle of a nautical chart is figuring out what symbols mean.
A set of weird looking triangles?
A symbol like this * ?
The numbers tell you the depth of the water at average low tide.
The triangles are a set of tide rips, and the * is an undersea rock.
Best of all, the secret code to deciphering all these symbols isn’t a secret at all.
It’s all in a chart called “Chart No. 1” (like all US nautical charts) for no money whatsoever from the US government.
Key West with the GeoGarage platform
Find the Marine Life
With the mastery of a nautical chart, it’s easy to find coral reefs, tidepools, and other places where sea life gathers.
Look for sets of rocks in shallow water where an olive-drab chart color (which means it covers and uncovers as the tide goes in and out) means that rocks will be exposed, and go at low tide.
If there are some of those weird triangles nearby even better: tide races mean strong currents, which mean more marine life.
Another rule of thumb: the more complex the undersea features look on the chart, the more stuff will live there.
NOAA Tidal info (GeoGarage platform)
Find a Cool Beach to Explore
Likewise, you can use a chart—often better than a map—to find a new secret cove or a beach to explore.
The chart will show you how much a beach will be walkable at low and high tides, and whether it will be an unbroken stretch of sand great for running, or a rocky complex shore with lots of interesting rocks and coves.
Of course, you’ll need a tide table to figure out when to go there.
Los Angeles, California (GeoGarage platform)
A fishing-mad friend of mine who lives on the California coast claims that his most important piece of fishing gear is his chart.
It tells him where the undersea rocks are, and how far down they are.
As he told me, “There’s no point in dropping a lure in 12 feet of water is the rock is 14 feet down.” From the number of rockfish and cod he hauls up, he’s right.
Maine’s Revesing Falls (GeoGarage platform)
Find Tidal Rapids
Charts will tell you where you can watch one of the ocean’s weirdest and coolest phenomena: ocean tidal rapid.
Where ocean currents flow through narrow passes, they accelerate, forming a whitewater river….that reverses direction.
They’re incredibly cool to watch, and attract everything from marine life to fishermen and whitewater kayakers.
Some are famous, like Washington’s Deception Pass, Maine’s Revesing Falls, or the Straits of Messina between Sicily and Italy, that Homer made famous as the whirlpool Charybdis, in the Odyssey.
Miami with the GeoGarage platform
Go Paddling or Rowing
And if you get in a small boat—any small boat: rowboat, canoe, dinghy, sailboat, kayak, or outboard—you’ll want to know how to read a chart.
Act Like an Old Salt
Best of all, reading a chart can also help talk like an old salt.
Impress (or tease) your friends with phrases like “2 fathoms below mean lower low water” or “that lighthouse over there flashes every 39 seconds and is visible for 5 nautical miles”.
They’ll stop rolling their eyes when they realize that you know where to catch fish, and they don’t.
Nautical charts for anywhere in the US are free for download.
The coast guard knows its cheaper to put them all online than to have to send out the chopper or rescue boat when you get in trouble because your boat ran aground or waded out into a quicksand mudflat you didn’t know was there.
You can buy paper charts too–which cost a few bucks to cover the cost of paper and ink.