Tender Fishfinder

I was thinking that a portable fishfinder, run by batteries would work well in the Tender. The transducer is temporarily adhered to the underside of the boat by a suction cup.
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This Humminbird model is supposed to be accurate up to 600 ft. There are other makes and models available - some in color, with GPS functions, and pretty pricy.
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This B&W model seems to have the basics, reasonable resolution, temperature and deth gauges I'm concerned about battery life. It you don't get more than 12 hours, it would be a pain.
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There should be cod and flounder in Marblehead Harbor over the cold months, and this baby could help me catch them.