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Know-how: Reading the water

Reading the Water

Water. From a distance, we can contemplate its beauty. It’s restful to look upon and relaxing to listen to, but it is never still. Breezes ruffle the surface, and winds make waves and swells. Tides make water rise and fall, while currents move it horizontally. There’s a story here. It behooves us to read that story.

Anticipating the conditions around and ahead of you is part of the dictum: “A seaman uses knowledge, skill and experience to avoid circumstances where he’s forced to use that knowledge, skill and experience to get out of trouble.” You may, with a proper read of the water, keep Murphy and Mother Nature at bay.

1. Current, generated by flooding and ebbing tides, causes volumes of water to move in and out of restricted areas such as bays, sounds, estuaries and inlets. Current often appears as a smooth area with flow lines at its margins. Look into any stream, and you’ll see the surface effect of current. You can see the effects of current on buoys as they tilt in the direction of the water flow; this is known as set. If there are pilings, the effect of current can appear almost as a bow wave up-current and as a wake or a swirl down-current. Current can increase or decrease boat speed, depending on whether you are running with or against it, or it can alter your course.

2.Wind blowing against current will shorten wavelengths, make wave forms steeper and increase their height, often leading to breaking waves. It’s one of the reasons you shouldn’t attempt to run an inlet if wind and current are in opposition to each other. Every boater in tidal waters should have on board and understand tide and tidal current tables. From seaward, it’s difficult to identify the effects of wind against current, except that on a clear day the air immediately above the inlet may appear slightly darker. Remember, a north-setting current flows against a north wind.

3. Where two currents meet or when current flows over an irregular bottom, a rip — an area of choppy, turbulent water — may develop. A strong current flowing around a headland or encountering a steep irregularity on the bottom can form a race — an area of increased current flow accompanied by turbulent water, standing waves and breaking seas. Even at slack water, rips and races can be identified by a line of scum on the surface along their boundaries. In extreme cases, tidal currents moving rapidly through a narrow passage or over an uneven bottom can cause whirlpools to form. It’s fairly easy to spot the effects of current opposing wind, but when wind blows with the current wavelengths increase and the height and steepness of waves is reduced. For a slow boat this can cause problems, because water flow can reduce the effectiveness of the rudder, making steering difficult.

4. Breaking surf over a limited area usually indicates a shoal of some sort — for example, a bar across the mouth of an inlet. This is easy to spot when you can see the whitecaps and curl of the waves. When viewed from upwind of the shoal, however, seeing the disturbance is more problematic, the effect being more subtle. Look for an irregular silhouette to wave backs.

5. Wind-driven waves and swells will heap up and break across the mouth of an inlet as the volume of water becomes constricted by decreasing depth and the boundaries of the inlet. Again, it’s very difficult to see from seaward except in clear weather, when the spray can appear to darken the air right above the inlet. Close in, you may be able to see spray reflecting sunlight. My advice is to avoid leeward inlets or other restrictions to the passage of water.

6. Shallow water usually appears lighter in color — Coke-bottle green or light brown — because of light reflecting off the bottom. Coral heads and rocks usually are a darker brown color.