His cranberry fields flooded with 6 inches of water, Dan Brockman drives his new harvesting machine — romantically named the ruby slipper — through the vines. Steel, finger-like rods submerged in the chilly waters quietly nudge and shake the plants.

Berries float to the surface, a sea of red forming behind Brockman’s tractor as he drives.

His invention — five years in the making — promises a much faster way to harvest the popular fruit that is a staple of Thanksgiving Day tables and a $200 million-a-year industry.

“If it works as well as it appears it does, yes, it will revolutionize cranberry harvesting,” said Teryl Roper, a fruits crop specialist and professor of horticulture at the University of Wisconsin-Madison. “I don’t know why no one thought of it before. It is elegantly simple.”

The ruby slipper is an alternative to expensive mechanized water wheel beaters that have been used for decades each fall to harvest cranberries. Brockman’s invention has no movable parts other than spring-loaded arms upon which metal finger-like rods are mounted. As the device is pulled or pushed through flooded cranberry vines with a tractor, the arms follow the contour of the ground and the rods shake off the berries — much like someone shaking a small apple tree so the fruit rains down.

The berries float to the top of the water, where workers gather them together and pump them into trailers and trucks for processing into juices, sauces and other products.

By comparison, the self-propelled machine now used throughout the industry features a rotating beater similar to rotating cutters on old push lawn mowers that knocks the berries from the vines as the harvester slowly drives down flooded fields.

Brockman, 47, invested $30,000 developing his ruby slipper. A patent is pending.

“I didn’t build it with the concept that I am going to build something that everyone wants to buy. I was building it so I could harvest my crop better and more efficiently and it just happened that a groundhog finds an acorn,” Brockman said, laughing.

BDT Inc., a Wisconsin Rapids manufacturing company that bought the rights to build the machine from Brockman, has sold eight ruby slippers so far — costing from $7,000 to $9,000 depending on the width — and all the customers are happy with the results, engineer and co-owner Dave Dix said.

It’s the biggest technological development for the cranberry industry in 20 years, Dix said.

Many larger growers now use three workers each operating a self-propelled water wheel beater, some costing up to $40,000 each, Dix said.

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