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Reading The Water

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"It's Better In The Bahamas," the ads proclaim.

What could be better than warm, clear waters that flash a tropical spectrum of cobalt blues, turquoises, aquamarines and water the color of air. How beautiful!

But seeing the water below your keel shrink to a wafer-thin margin may not feel so good. Florida, the Bahamas and parts of Mexico are noted for skinny water. These popular cruising grounds can seem alarmingly shoal to first timers. With the exception of Florida, they are marked with the most casual of aids to navigation.

It's enough to make newcomers creep along at bare steerageway filled with doubt and indecision. Yet locals go boldly through passes and between unmarked flats without a care. How do they do it? Well, they're reading the water.


The array of vivid blues, greens and browns that look great on travel posters also speak volumes to tropical yachtsmen. The colors tell both water depth and bottom configuration. It's precisely because the water is both shallow and clear that this is possible. Sunlight pierces the water, strikes the bottom and, depending on what's down there, produces a telltale color.

The blues are safe water.

"Blue, blue, go on through."

Greens mean it's starting to shoal, but still safe for all but large ships.

"Green, green, nice and clean."

The browns are trouble-don't go there.

"Brown, brown, run aground."

White water, as in gin clear, is most confusing of all. It marks a sand bottom that might be inches or fathoms deep.

"White, white, it just might..."

Mnemonics are a great memory aid but there is more to reading tropical water than a few lines of rhyme.


For water reading to work one needs a few things, sunlight being the most important. No sun, no color. You'd better not go in unless you're sure of your position. The sun must be high enough in the sky to produce good color. It doesn't work at dawn or dusk; the angle is too low. It doesn't work if it's raining, or cloudy, or wind has the water surface greatly disturbed, or a storm has churned and filled the water with sediment that blocks sunlight and obscures the bottom. And of course, it doesn't work at night.

The best condition for water reading is with the sun high and slightly behind you, shining over your shoulder. Getting as high as possible on a boat maximizes the view of bottom colors. Using polarized sunglasses increases the contrast between colors and makes things easier. If the sun is off the bow, polarized lenses also filter out glare on the water's surface. This helps a lot.

The varying shades of blue, green and brown go something like this: A purple blue indicates very deep water where shoaling is not an issue. As the depth decreases the richness of the blue gradually washes out and is replaced with lighter shades. When the color lightens to a pretty powder blue and details on the bottom can be distinguished, you're in the 30-foot depth range.


As you go shallower still the water picks up a greenish tint. When the blue disappears completely and all that's left is green, the depth sounder should be reading somewhere around 20 feet or less. As the green starts to lighten and fade it's time to watch your 12 o'clock for darker forms in the green. They appear brown, reddish or sometimes black.

They could be patch reef, grass beds or, most dangerous of all, isolated coral heads. Coral heads are huge living boulders that can grow 20 feet in diameter and to within a few feet of the surface. The extreme clarity of tropical waters can make it difficult to determine if the top of a coral head is 10 feet down or just below the surface.

I always play it safe and go around them. When green gives way to yellow, you've entered singledigit territory-the paler the yellow, the thinner the water. When the yellow becomes so pale as to be completely transparent, you can get out and walk.

A sand bottom can be the most difficult to read. If the sun is high and the water, wind and current are still, 30 feet of water can look 30 inches. Your boat appears suspended in air. It's quite amazing. As stated earlier, any color not blue or green should be suspect, including no color.

Water reading is intuitive and user-friendly. Once understood, newcomers to the tropics quickly master the skill. It's important to note that the previously described color change is not an orderly progression. Mottled is the best way to put it. Light blues and greens freely intermix. Yellow sand banks inches deep have green, 7-foot deep channels winding through them. Areas of greenish-brown turtle grass are studded with orange coral heads. Danger lurks for the non-observant.

Skinny water is no place for an autopilot. However, once water literacy is achieved, most visitors to the tropics find themselves comfortably exploring mangrove creeks and deserted backwaters with a scant 12 inches under the keel.