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Sailing-by-color: a vital skill for tropical sailors

Tropical waters provide sailors with some unique clues about what lies beneath the surface, thanks to the color shifts that accompany changes in depth. Unfortunately, "sailing-by-color" works only in good weather, with the sun overhead; even a passing cloud is enough to confound the visual navigator. Nevertheless, it pays for all tropical cruisers to perfect their sailing-by-color skills, especially when heading into remote areas where markers may be few and far between. On this page we present a few examples of how colors can help you navigate in the tropics. For more on this subject see Chapter 4 (Navigating in Tropical Waters), in Tropical Cruising Handbook.

Photo: Recif du Prony, New Caledonia
To the right of the reef above lies an extensive and sheltered bay. Although easy to see on a clear day, this reef can be very hard to spot on a calm, overcast day (when colors are muted, and there is no surf break). Were it not for the marker on the reef's right-hand tip, it would then be very easy to turn into the bay too soon, and thus end up on the reef.

Photo: Reef Pass, Solomon Islands

The channel through the reef above (indicated by the red marker in the center of the photo) is clearly visible. Note that the reef in the foreground extends a short distance to the left of the reef marker.

Photo: Sandy bottom, Isle of Pines

Shades of blue. The change in color above indicates an abrupt decrease in depth, from the navigable water in the foreground (8-10' deep) to shoal water near the horizon (5' or less).

Photo: Hermit Islands, Papua New Guinea

The only safe passage between these islands (if there is one) is on the left side of the photo. The light green band extending out from either side of the island in the foreground indicates water too shallow for all but a dinghy.

Photo: Reef marker, Solomon Islands

Here the presence of a reef beyond the marker is confirmed by the surf break, and hinted at by a light greenish color between the marker and the surf break. A cloud has momentarily blocked the sun, however (note the shadow extending through the center of the photo), and the boundaries of the reef are impossible to see.

Photo: Reef marker, Solomon Islands

Once again a cloud has interfered with visibility, and the reef this marker is warning of can't be seen.

Mark Smaalders and Kim des Rochers 2002