Sea Savvy - Colors are key to reading the water - Soundings Online

Sea Savvy - Colors are key to reading the water

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Changes in hues mean changes in depths in the clear waters of the Bahamas

Changes in hues mean changes in depths in the clear waters of the Bahamas

I’m not sure how many official working aids to navigation there are in the Bahamas, and I don’t think anyone else is, either. I am sure that it’s not many, and there are thousands of square miles of water. But Bahamian friends tell me, “No problem, mon, no problem,” because much of the time they can see the bottom. They also know important tricks, like the significance of bird legs (more on that later).

The water’s so clear in the Bahamas that in our early days of cruising there we’d estimate how much the currents were pulling us off course by looking at the fan coral and sea grasses on the bottom. They would point in the direction of current flow, and fan coral would bend depending on the speed of the current. In areas like this, you don’t need buoys or day beacons. Learning to read the water in the Bahamas is important for cruising there, and many of the lessons are helpful for reading opaque waters in other areas, including the United States.

Some ask, Why bother reading the water when we have GPS and electronic charts? Indeed, these have made navigation much easier and safer. We love our C-MAP cartridges, Furuno GPS/ chart plotter, and radar on Chez Nous, the Gulfstar 53 motorsailer we live aboard. But operating a boat without developing underlying navigational skills is like water skiing without a life jacket or knowing how to swim.

Even if you have complete redundancy in your electronics, you can still have problems aboard that render them useless. Also, satellites can go down, and the system can be made unavailable to the recreational user in times of national emergency. In addition, there are areas, particularly in the Bahamas and Caribbean, where GPS waypoints may be a little inaccurate unless derived by actually taking a working GPS receiver to the precise site. This is because many of the underlying charts aren’t precisely accurate. Also, shoals shift regularly, particularly during severe storms. An error of only a few feet is enough to be fatal when you’re negotiating reef-riddled inlets or waters with coral heads.

Color clues

In the Bahamas, and to a lesser extent in areas where the water isn’t as clear, color is a primary indicator. There are some basic color guides for navigating Bahamian waters, but as is true with most forms of navigation, many things can cause exceptions to the rules. Here are some general guidelines and important deviations.

Blue, green or turquoise water of a bright color indicates that the depth is probably adequate for most pleasure boats to navigate. The darker the color appears, the deeper the water. If the blue, green or turquoise are very pale (more white or yellow than blue or green) the water likely is too shallow and should be avoided. Deep blue “highways” are very obvious where they flow between shallows, and deep ocean water sometimes looks violet. The darker colors of grass can cause confusion, but I’ll talk about that below.

White water indicates a very shallow sand bank.

Yellow water indicates a shallow bank, either of sand, marl (rocky hard sand) or rock.

Light brown or yellowish brown water indicates a shallow rocky bar, usually called a brown bar. If it is spotty looking, there may be coral growth very close to the surface. Darker or yellowish brown, with some green or blue over it, also indicates a rocky bar but one that is deeper beneath the surface. Avoid trying to cross over any area that looks more yellow or brown than blue or green.

Black water indicates coral but with some depth of water over it. The coral may or may not be deep enough for your boat to pass over, so it is best to play it safe and avoid black areas. The black may appear as spots (soft coral such as fans or detached growths) or a large solid clump (coral head).

Problem bottoms

Coral attaches only to rock, not sand. If the water is bright blue but you can see yellow, brown or other light colors (white if the coral is dead) just beneath the surface, there may be a very tall growth of coral close to the surface, like elkhorn coral or a tall barrier reef such as those outside Abaco and Andros. Stand off.

On the ocean side of an island, breaking waves often alert you to this danger. Dead coral heads maintain their shape and hardness, while their lack of color makes them difficult to distinguish from the surrounding bottom. They can still sink your boat. As you’ll see, the appearance of underwater grass plays an important role in distinguishing coral.

Grass presents special difficulties when you’re trying to read the bottom. If it is thick it can look very dark, somewhat like deep water. Once you get close you likely will realize it is grass, but by then it may be too late. Thin grass will appear to be a darker, duller blue or green, again like relatively deep water. Also, it may grow in thick, dark patches that easily can be mistaken for coral heads.

But while grass can cause confusion, it can be helpful in one important situation. Coral heads that look black against blue water usually have a ring of lighter blue around them. This is because you’re seeing a circle of sand around the head, where the fish in the reef have denuded the bottom of its thin layer of grass. This ring of lighter water is one method for distinguishing coral heads from grass patches. Also, coral heads often are round and detached, while grassy patches likely are to be irregular and connected.

On wide, flat areas of bottom, grassy ridges or clumps can look very dark compared to lighter-colored-blue adjacent sandy areas. This can cause confusion when trying to distinguish the deeper water. A general rule here is that if there are both sand and clumps or ridges of heavy grass, the sand usually will be deeper, often by several feet, even though it is lightly colored. The current has swept the loose sand away, leaving the higher ridges or clumps of grass.

Narrow channels over hard bottoms, where currents rush around rocks or between cays, may have a heavy-but-even growth of grass over the deepest part where the sand has settled. These channels look like dark lines and indicate the deeper water.

Complications

There are other factors that play important roles in reading Bahamian waters. Clouds on an otherwise sunny day can cast dark shadows on the water. These can be mistaken for coral heads or grassy patches. If you suspect a cloud is causing the dark area on the water, watch for irregular, changing shapes and movement on the surface, and — this may seem obvious — look at the sky. It’s best to err on the side of caution and avoid the spot.

Sand and silt can make the water cloudy and difficult to read. Fish mud, for example, makes deep water appear white and shallow. This phenomenon occurs often in the Little Bahama Bank where large schools of fish feeding on the bottom stir up the soft sand, turning the water white over areas sometimes several miles broad. Also, if there has been dredging in a harbor, it takes a long time for sand and silt to settle out of the water enough for you to read the bottom. And tides may carry it far from the dredging site. Lastly, storms — prolonged westerlies in particular — can turn the banks and island waters milky white.

Algae growth in the spring and summer can make most Bahamian waters distinctly greener than the bright turquoise blue of winter. Clear blue waters can turn cloudy and pea green in a matter of days.

Sunlight — both the amount and direction — is critical to reading the waters. This is so important that the primary rule for piloting in the Bahamas is to travel only during daytime when the light is good. A corollary is to make landfall or negotiate shallows only in good light, in order to read the bottom. Good light is when the sun is overhead or behind you, as long as it isn’t too low. Bad light is when the sun is low or in front of you (in your face) so that it reflects off the surface and you can’t see through to the bottom.

We’ve seen boats lost simply because the skipper took off out of a cut in good weather and light, but didn’t realize the significance of time of day and light when he planned to re-enter. Going into a cut or inlet in the evening will result in the sun being in your eyes if the island or bank is to the west.

There are several other light situations that affect visibility. If it is flat calm, the water surface becomes totally reflective regardless of where the sun is, and you can only see the bottom directly beneath you. Early or late in the day when the sun is low on the horizon, it is impossible to see the water color ahead. Extremely rough water, rainy days with heavily overcast skies, and light overcast weather with a high, thin cloud layer producing glare can all make reading water depths difficult. Polarized sunglasses help, as long as there’s light. Increasing your height off the water is very helpful, and you should have a plan for getting a lookout as high as possible on your boat for tricky situations.

Although you should only travel in good light, there are other daytime conditions that you wouldn’t expect to be good, but which can provide some visibility if you are caught out. You can usually read the water fairly well in heavy overcast without rain, or in very light rain. Finally, during the full moon in flat, calm conditions the bottom can be almost as bright as in daylight, especially in shallow, sandy areas. But navigating isn’t recommended then because the passage of a cloud leaves you blind.

Muddy waters

When we return to the United States and find aids to navigation everywhere, we don’t feel any better about not running aground. We’d much rather read the waters than trust the government to tell us where the shallows are. In the Bahamas it’s easy to compare surface phenomena with bottom characteristics because you can see it all. And seeing these relationships there helps with learning to interpret surface signs in muddier waters.

When the water is muddy, lighter colors usually mean shallow water. Also, distinct lines of color changes usually indicate tidal change demarcations. When you see these clear definitions, you can normally assume you’re looking at deeper channel water because it’s carrying the tidal change. Shallow areas usually don’t have enough current to generate distinct lines of tidal demarcation. These lines are seldom straight, but if they’re swirling, they may indicate an obstruction on the bottom or the existence of a side channel through which the tide is rapidly flowing. Side channels often cause the buildup of shoals where they enter a main channel, necessitating extra caution.

On the surface

Other surface factors help indicate conditions. Riverboat pilots looked for swirls and eddies on the water’s surface, which tell many stories. While a harmless obstruction far under water can cause a noticeable upwelling, the same is true of shoals and shallow obstructions. Upwellings from larger obstructions like shoals may not be easily noticeable if there is a slow-moving current and the shoal is broad and gradual. However, if the water is rippled by a breeze, the upwelling may diminish the ripple, resulting in a smoother surface that indicates the shoal. Conversely, if a stiff breeze is generating waves, these may increase and show a breaking effect as they reach a shoal that is otherwise invisible.

Rounding the bend

Navigating any river, creek or cut usually involves rounding bends. Characteristic of most turns in a channel is the buildup of shoals, usually where the main flow of the current is sheltered by the bend or has eddies resulting from the bend. These factors allow it to dump sediment to the side. But often in tidal areas it’s difficult to know, without local knowledge, which side of the bend has this characteristic.

If you watch the surface of the water for telltale signs, you may be able to determine the location of the shallows. For example, fast-moving water with a still surface probably will be deep. An area around the corner with a very slow-moving surface is more likely to be shallow. Eddies resulting from currents rounding turns, while they can occur over shallow water, usually are more likely to occur in deeper water or at the edge of the shallows. Also, a concave shoreline on one side of a bend likely indicates a shallow area.

Floating clues

Things floating on the surface can give clues as to what’s below. For example, if you see a line of blue-crab pot floats in a river or creek, you can often assume that it’s along a drop-off. Not all crab-pot floats are along drop-offs; many are set in very deep water. But a line near shore is a good indication of where the mud bank falls away into the channel. If you’re scooting along in fairly shallow water in your dinghy or other small boat and you see crab-pot floats, you can usually assume that the water will be deep enough for your dinghy, as long as you aren’t seeing the tops of the crab pots breaking the surface.

Weed lines offshore in the ocean are familiar to fishermen because they mark tidal lines, and bait fish and larger predators often are hanging out underneath. If you see these in shallower rivers or creeks, you may be looking at the border of a tidal change, as previously discussed. Sometimes this is the only indicator, as when the color of the two bodies of water is the same.

Clumps of grass floating in rivers and creeks can be quite confusing. Some are large enough to look like small islands, and frequently float along in deep water. They are most likely to occur after storms, heavy rains and coastal flooding. Unless they appear to be stuck on the bottom and stationary, we generally give them a wide berth but don’t assign much other significance to them. If the current is moving past them at a high rate, assume they’re anchored to a bottom that may not be far below.

Other debris from flooding can include small logs, snags and large trees. In wooded areas, it isn’t unusual to find seemingly small sticks poking through the surface, only to find an entire tree beneath the water as you approach. If the stick appears to be moving through the water, be particularly careful; this indicates it is anchored against the current by the rest of the tree or branch below the surface.

The tips I’ve discussed here aren’t foolproof, and it’s important to use all relevant information, common sense, and all facets of prudent navigation. It’s always better to err on the side of safety. However, there’s one tenet that comes very close to being an absolute: Remember the rule of the seagulls.

These birds often sit on the surface of deep water in flocks. Sometimes they do so when a storm is imminent; sometimes they’re resting between feeding frenzies of the bait fish we hope to see while we’re fishing. But seagulls also like to walk about on shoals under an inch or so of water. That’s why it’s important to have a good pair of binoculars. Sighting of sea gull knees ahead is a sure sign you’re bound for trouble. And that’s the significance of bird legs.