In Our Wake: A View from the Bottom

You probably don’t give a lot of thought to your depth and fishfinder but maybe it’s worth taking a moment to appreciate what it does—and its most remarkable inventors. Prior to the early 1900’s, measuring depth with a piece of line—with maybe a grease-covered rock attached to sample the seafloor—hadn’t changed all that much in a few thousand years. The first to crack the electronic code was a Canadian pioneer in electricity and radio named Reginald Fessenden. Best known for the first two-way radio broadcast (a transmission between Massachusetts and Scotland), Fessenden built a crude device that bounced sound waves off the seafloor. Because he knew how fast sound traveled in water, when the 4,800-feet-per-second echo returned to a shipboard amplifier, you could determine roughly how deep that water was. 

The problem was, Fessenden’s invention only worked in deep ocean. In 1922, a colleague named Herbert Grove Dorsey devised an ingenious way to amplify the sounds electronically with a state of the art device called a vacuum tube. Its electric sound-receiving signal was then passed on to a tiny, flashing neon tube. “This flash will shine through the glass, opposite some mark on the scale, six fathoms for example, if that happens to be the depth of water through which the ship is passing,” Dorsey said in a 1932 radio broadcast. “Four times a second the red light flashes at six fathoms, thus measuring a time interval of only fifteen thousandths of a second, and you read the depth as easily as you read time on a clock.” Dorsey’s Fathometer, the precursor to every sonar device you see today, was a wild success.

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This article originally appeared in the January 2024 issue of Power & Motoryacht magazine.

Source: https://www.powerandmotoryacht.com/column/in-our-wake-a-view-from-the-bottom