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DEFENCE 2000 Defence was a privateer during the American Revolutionary War. She was the largest American vessel sailing in the Penobscot Expedition, an operation that ended disastrously for the Americans. The American fleet met a Royal Navy task force and was bottled up in Penobscot Bay. As British warships closed on the Yankees, crews scuttled their vessels to avoid their seizure. Archaeologists led by Professor David C. Switzer excavated Defence in the late 1970s and early 1980s. The vessel lies in shallow water (about 6-8 m), ideal for diving operations although the visibility is generally very poor (< 2 m). In the fall of 2000, MIT DeepArch traveled to the site to run tests of our high-frequency, narrow-beam subbottom profiling sonar. The sensor was tracked using SHARPS, (Sonic High Accuracy Ranging and Positioning System), a precursor to David Mindell's EXACT wireless system. Archaeologists Professor Switzer and Dr. Warren Riess (UMaine Darling Marine Center) collaborated on the project, contributing logistical support and knowledge derived from years of experience on the site.
Darling Marine Center Research Vessel Ira C, a terrific platform for inshore projects.
Cable management is one challenge posed by SHARPS. Here DeepArch's Katy Croff tends SHARPS cables and transducers on an ad hoc carrier.
The SHARPS transducers operate on line-of-site. It's important to keep them clear of the seafloor or any obstructions to line-of-site. Here Brendan Foley inspects PVC transducer mounts prior to deployment around the Defence site. These mounts proved versatile, stabile, and were inexpensive to build.
The subbottom transducer with three SHARPS transducers mounted on it. This allowed us to track the attitude of the subbottom 'ducer. Where we would be without duct tape and tie wraps?
UMaine diver John Varinec, Warren Riess, David Switzer, Katy Croff, and Brett Lockyer with the subbottom transducer on the back deck of the Ira C.
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