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180 Mowing the Lawn Perhaps this would be a good place to discuss how maritime archaeologists find shipwrecks. The process starts with archival research. This means dreary hours in library stacks, historical society manuscript collections , public record offices, and newspaper archives and, today, online. Libraries contain a wealth of primary and secondary sources related to shipbuilding, shipping, shipowners, and shipwrecks. Manuscript collections at local historical societies may contain personal diaries and correspondence of seagoing families, shipping records of local merchants, and ship logbooks. At the various public records offices, one finds the deeds and plats regarding shipyards, ferry landings, and public wharfs as well as the tax records, land records, wills, and probate inventories of ship captains, shipowners, and shipbuilders. Newspaper archives give us contemporary accounts of ship launchings, ship voyages, and shipwrecks. Nowadays the Internet provides forums where archaeologists exchange information about current research pertaining to ships, shipwrecks, and maritime artifacts. Surprisingly good sources of information about shipwrecks are “locals.” Shrimpers know the precise locations of objects that snag their nets. Anglers have their favorite offshore fishing spot—that raised bottom where fish seem to gather. Objects that catch shrimp nets and raised bottoms fished by anglers are often vessel remains. Local “historians” and sport divers are other good sources of information. Once the location of a shipwreck has been pinpointed as best as possible from written and verbal sources, the next step is finding it. In the old days, this was a hit-or-miss endeavor. Mostly miss. Depth finders have been used to find places where the bottom has relief. Grapple hooks and small anchors were dragged across the bottom, hoping to catch ship remains. If visibility allowed, divers could be towed behind a boat to survey the bottom. Of course this could be problematic if there were Mowing the Lawn 181 poisonous jellies in the water and the towing boat’s propeller chewed them into small enough pieces to infiltrate wet suits. There is even a story of a researcher who lowered a tape recorder microphone to the bottom and used the changes in noise as the microphone skimmed over the bottom as clues. I kind of doubt this would work with any kind of effectiveness, but I have no doubt the story is true. If these crude techniques were unsuccessful, divers could search for vessel remains. Using a variety of search techniques—circle searches, jackstay searches, swim line searches, grid searches—divers covered the area until they found the target, or not. Most often not. Today searching for a shipwreck has gone high tech. Oh, we still do research in libraries, historical societies, public record offices, and newspaper archives. And it is still just as dreary. And we still talk to local sources, but actually finding a wreck now involves using remote sensing equipment—magnetometers, side-scan sonar units, and sub-bottom profilers. For the marine archaeologist, these instruments are the equivalent of the long-range sensors on Captain Kirk’s starship Enterprise. They are as sophisticated as they are expensive. Magnetometers detect variations in the strength of the earth’s magnetic field caused by the presence of ferrous metals, that is, iron and steel. The advantage of the magnetometer is that it can detect objects buried below the bottom, provided, of course, that they are made of ferrous metal. The larger the object, the deeper it can be detected. We found the top of the H. L. Hunley under at least two feet of sand. We first came across the remains of the USS Housatonic a good six feet below the bottom. A magnetometer can locate shipwrecks such as these even though they may be much farther below the bottom. Magnetometers are towed behind a boat, keeping them far enough back not to pick up the ferrous metals of the boat itself. While magnetometers are good for finding metal, it is almost impossible to determine what that metal constitutes. For this there is the sidescan sonar. Side-scan sonar takes a “picture” of the sunken object. By sending out sound pulses and analyzing the echoes, something like a black-and-white picture of the bottom under and to the sides of the survey boat is recorded. The sound pulses are transmitted from a towfish, but they can also be transmitted by hull-mounted devices. On early models the sonar picture was recorded on a paper plotter. Nowadays it’s all on computer. Of course for the side scan...

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