Palette of blues

When voyaging anywhere between 30°deg; N and 30°deg; S — the Bahamas, Belize, Brazil, Galapagos, the Great Barrier Reef or the Seychelles — water color is a key piloting tool. After the GPS, your sextant sights, the radar and the voyaging guides have delivered you close to your destination, you will have to rely on your eyes to find the way into the anchorage. Often natural phenomena overhead, like clouds, calms or rain, and others below, like coral reefs or sandy shoals, will make the job harder. Often it will take forethought, patience, strategy and even gadgets to earn the rewards of perfect places.

In model tropical voyaging, the seas are clear, the sun always shines and each shade of the blue sea surface corresponds to a certain range of depth. The darker the blue, the deeper the water: shallow sandbanks glow brightly and coral heads loom menacingly. The rule works well from the cobalt blue of very deep water to about 8-foot-deep channels, which paint a lighter, but noticeably more intense, blue than the turquoise depths of 6 feet and less. The type of bottom really defines the color nuances of lesser depths. A shoal of grass may look deceptively deep, and a deep channel with sandy bottom will look shallower than the same depth filled with rich coral growth. Only by comparing depthsounder readings with the colors of the water can one learn how the type of bottom affects the shades of color. For U.S. East Coast sailors, the waters of Bermuda and especially the Bahamas, both extensively covered by voyaging guides, offer the perfect opportunity to practice piloting by eye.

Having the sun high behind you makes the job much easier. As the sun slides down, the picture ahead becomes less obvious and the navigator will see better from a higher position on the ratlines or even on the spreaders. The low sun shining from abeam makes the shoals less distinct because the rolling sea surface reflects the light in the wrong direction. When the sun altitude drops below 60°deg; somewhere ahead of the course, you should head for another place, as the glare on the water will prevent you from seeing anything, no matter how high the navigator climbs. This is where good planning comes in. Schedule an early arrival when the sun is still high and approach at an angle that avoids steering against the sun. In the Northern Hemisphere, when voyaging an island group that stretches roughly north and south (Belize’s barrier reef and the Exuma Islands in the Bahamas come to mind), begin exploring from the southern end in winter when the sun sets south of west. That way, at the end of the day, you approach anchorages with the light slightly behind the vessel. In summer, begin voyaging the same islands from the north, since the sun sets north of west.

All this strategizing works great with perfect weather, but even those famous, fluffy cumulus of the trade winds can complicate the picture. They cast fleeting shadows that look just like big patches of coral. You may have to slow down, take a good look and decide whether dark spots ahead stay in place or are moving downwind. Winds, too, influence pilotage by eye. You will get help from a moderate breeze and a wave-wrinkled sea in getting the palette of blues. However, prolonged strong winds put bottom sediments in suspension, diluting colors that correspond to various depths and blurring their apparent edges. It takes only a firm breeze to lower the water visibility in an area with a soft bottom, like most of the Florida Keys. A gale will stir up even the Great Bahama Bank with its firm, sandy bottom. Tidal currents add another factor to consider. Even with a gale blowing, the incoming tide brings clear ocean water into the deeper channels leading onto shallow banks. On the other hand, the outgoing tide will carry out the silted sea and blanket not only the channel but even the ocean waters surrounding it. Remember the tides when running for shelter from Exuma Sound into Big Rock Cut, Galliot Cut or any other passes onto the Exuma Banks.

Time of the year may introduce unexpected complications. Bahamian waters are famous for their clarity, yet in late spring and summer, when algae blooms on the banks, the turquoise seas turn green and soupy. In the Abacos and around the Berry Islands, spawning fish cause vast, light-colored patches that look like shoals. All this biological activity often coincides with the rainy season and erratic, variable cloud cover. Conditions like these once did us in — mainly because I lacked polarized sunglasses, an important aid to eyeballing.

We were tacking through the Middle Bight of Andros when a layer of clouds moved across the sky. The dark patches of coral bordering our blue channel disappeared into a grayish glare ahead. I needed my polarized glasses, but they had gone overboard a couple of days earlier. We continued anyway, thinking ourselves familiar with the channel from previous visits. But soon, despite watching the depthsounder, we crunched to a stop before we could tack away — on the falling tide, too, so it was well after midnight before we finally pulled ourselves free. Polarized glasses would have cut the glare and revealed the outline of the shoal that bordered our course. When using these glasses, notice that cocking the head sideways often intensifies the polarized image — just enough to distinguish details on the sea bottom. Needless to say, since our Andros grounding, we carry spare polarized sunglasses and wear glasses secured around the neck with safety lanyards.

Unfortunately, at some point we all encounter glassy, calm conditions when the sea surface changes into a mirror impenetrable to the eye, polarized glasses or not. If the sky remains clear, you can see details on the bottom 30 feet down but only a few feet ahead. Add a dull, whitish overcast to the calm, and even that luxury vanishes. Do not attempt going through shallow areas in such conditions. Stay at anchor, nap, read or best of all, go diving in places that are usually inaccessible in windy weather. If you must get to shelter because of imminent bad weather, send the tender ahead with sounding equipment (lead line, portable electronic sounder or a long boat hook) to guide the big boat in.

Even within the tropics, various geographical regions present peculiar challenges to the practitioner of eyeballing. Usually, it is the rivers that mess up the pretty picture. You can experience it firsthand along the south coast of Grenada, an island otherwise awash in clear ocean waters. In Honduras and Belize, the translucent waters of the offshore islands become opaque near the mainland, where rivers discharge silt into the sea. All along the coasts of Central America, the clarity of water suffers near river estuaries. As usual, not all is lost. This reduced water clarity encourages coral polyps, which are always in search of the right amount of light, to extend the reefs very close to the surface. As a result, navigable channels are obstructed by extremely shallow reefs whose tops are easy to see. Nevertheless, you still need your polarized sunglasses. The skies over Central America tend to draw a curtain of persistent overcast against the sun, and only with the help of polarizing will you see the coral shoals as brownish smudges seemingly floating on the surface. Plan your arrivals in the early afternoon when the sky often clears for a couple of hours.

Tom Zydler is a sailor, freelance writer and photographer.

By Ocean Navigator