Something for the bay lover on your list Gifts: From tide charts to state-of-the-art maps, a selection to delight even the toughest marsh-mucker.

On the Bay

December 12, 1997|By Tom Horton | Tom Horton,SUN STAFF

ECOLOGICALLY appropriate, elegant, useful and cheap -- here is why this columnist gives friends who explore the Chesapeake copies of Tidelog for Christmas year after year.

Bay boaters are inescapably shallow water boaters. At about a million feet long, about 100,000 feet at its widest point, with an average depth of 21 to 22 feet, the Chesapeake spreads far and wide, but exceedingly thin.

Much of this estuary's essence flows from its bottom being close to its surface, from the shoal draft design of skipjacks to jungles of light-loving underwater vegetation, and the surfeits of waterfowl and soft crabs, and water-fowlers and crabbers and crab-towns -- all linked to these grassy, fecund shallows.

Running aground, too, is a Chesapeake heritage. Maybe the best boat name I ever heard was The Despot's Heel, from a line in the state song, "Maryland My Maryland":

"The despot's heel is on thy shore ," and so, very often, was this boat.

This brings me to Tidelog, the first and foremost of some bay-appropriate Christmas presents reviewed herein. It is a slender almanac that, for $12.95, gives you a year's worth of high and low tides for every point in the Chesapeake -- and a lot more.

Tidal range (the difference between high and low water) averages only 2.5 feet for the bay. That compares with ranges of several feet to several yards around much of the North American coastline.

Still, given the bay's gently sloping shorelines, even a few extra inches of tide can make a difference in what's navigable of tens of thousands of acres of open water, and many miles of creeks and marshes.

This is especially true in small boats like the skiffs, canoes and kayaks I prefer. For example:

I often take groups canoeing through a series of interconnected, tidal creeks where you can paddle easily for miles beneath a forested canopy -- if there is enough water to make it through a few short stretches that are literally impassable, soft mud flats at most times.

For this, you need more than timing your trip with a high tide. You need a high tide that is on the high side.

The tides, you see, though they flood and ebb like clockwork (two highs and two lows every 24.8 hours), are in all other aspects quite variable.

On Sept. 18, for example, high tide at Baltimore was not just high, it was very high, 3.6 feet above normal low water. More than that, the low tide that followed was abnormally low, about 4 inches below normal.

A week later, on Sept. 26, the situation was quite different. The high was exactly average, 2.5 feet above normal low water, and the low that followed was not at all low. It was more than 6 inches above normal.

Taking friends through my little "northwest passage" of scenic tidal creeks, on Sept. 18 I would have been a champ. On the 26th, my name would have been mud.

Such differences in highs, lows and tidal ranges are predictable, having to do with the moon's orbit, its alignment with sun and Earth, and declination relative to Earth's equator. Tidelog explains all this clearly and succinctly.

And better than any of the many sets of tidal data I have seen, Tidelog presents the daily pulsing of the bay's tides in a fashion that is graphic and pleasing, using illustrations from Escher's "Second Day of Creation."

In the same handy format, it also shows you both current speeds and where, and in what phase, the moon will be in the sky during your trip on any given day.

Currents in the bay, while gentle like the tides, can be significant in paddle craft. Bucking the ebb tide on Sept. 26, for example, would have been fighting nearly one knot more current than on Sept. 18.

Tidelog also gives you planetary positions, solstices, equinoxes, meteor showers and eclipses, which add pleasantly to one's awareness of nature.

Two caveats about factors Tidelog doesn't predict. Winds often make Chesapeake tides higher or lower than forecast; and thermal expansion and contraction of water means summer tides stand as much as 7 inches higher than otherwise equal winter tides.

The guide also comes in a stowable, durable format perfect for small boats. You can get it in time for Christmas by calling Pacific Publishers, toll free at 888-TIDELOG, in Bolinas, Calif.

Mark Allan Born, the publisher, devised it, he said in a phone interview, in 1981 after many years of becoming "an expert in getting my boat off the mud."

Based on data from the National Oceanic and Atmospheric Administration, versions are available for the Chesapeake and most other regions of the American coasts. The company also offers IBM compatible software for Windows that will give you tides back to 1901, or forward to 2,100 for one or both U.S. coasts. As essential a feature of the bay as its shallowness is the huge, six-state, 64,000-square-mile basin, or watershed, that drains into it.

And now, for free if you act fast, you can get a gorgeous, state-of-the-art map of the watershed. Based on satellite imagery, it shows all the land uses, from forest and wetlands to farming and urban sprawl, that affect bay water quality.

It's free until Dec. 14 by calling the U.S. Geological Survey at 800-435-7627; after that it's $4, plus $3.50 shipping, by faxing 303-202-4693 (include VISA or Mastercard number); or writing USGS, Box 25286, Denver Federal Center, Denver, CO 80225.

Infrared photos take you to places maps cannot

Finally, a not-so-cheap gift for the hard-core marsh-mucker is a recent series of color-infrared aerial photos from Photo Science in Gaithersburg.

A 10-inch-by-10-inch print shows 25 square miles and costs about $60. I use them where maps won't do, for navigating through the incredibly complicated marshes in places like Dorchester County. They are available for the whole state, in breathtaking detail. Call 301-948-8550.

Pub Date: 12/12/97

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