Last month, Yoav Rosen received a United States patent (No. 6,764,363) for a device that he says will allow ordinary people to walk on water.

Mr. Rosen moved to the United States from Israel three and a half years ago, when his wife took a job as a researcher at the Dana Farber Cancer Institute. But Mr. Rosen, who had been a business and marketing executive for a software company in Israel, could not find an equivalent job here during the bottom of the dot-com bust.

“So I said to myself, ‘Why not start dreaming?’ ”

Many inventors are afflicted with an overabundance of ideas. Not so Mr. Rosen: “I just had this one idea,” he said. “But I’ve had it since I was 11 years old.”

His mother still keeps a picture of a water-walking machine he drew back then. “The design was all wrong,” Mr. Rosen said. “There is no way it would have worked.”

Of course, neither did Leonardo da Vinci’s water-walking device, which he conceived in the late 15th century. His drawing of it is housed at the Biblioteca Ambrosiana in Milan. Da Vinci’s invention – if it had worked – would have operated on a principal similar to cross-country skiing.

In the last 150 years, Americans have patented about 100 water-walking inventions. The first, in 1858, was by H. R. Rowlands, who lived in Boston, not far from where Mr. Rosen resides, in Newton, Mass. Most of the subsequent patents, Mr. Rosen said, are iterations of that same idea. “Unfortunately,” Mr. Rosen observed, “none of them actually work.”

Mr. Rosen’s device also resembles the 1858 design. His pontoons are made of Styrofoam and plywood, and are tethered together so the user’s legs will not spread apart while walking.

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