One reason that offshore wind has not caught on in the United States is the steep cost of erecting a tower in the water, but researchers at the University of Maine tried another approach on Friday by launching a floating wind machine. It is the first offshore wind installation in United States waters, according to the Energy Department, which helped pay for it.

The tower, launched in Brewer, Me., sits on three hollow concrete tubes and will be anchored in the Gulf of Maine. It is a mere 20 kilowatts in capacity, an amount of power that could be soaked up by a handful of big suburban houses on a hot summer day. But it is one-eighth the dimensions of the one the researchers hope to deploy in the next few years, a gigantic 6-megawatt model, with each blade as long as the wingspan of a Boeing 747.

Because of its location, it will have two big advantages over machines on land, according to Habib J. Dagher, a professor of civil engineering at the university. Onshore wind machines produce most of their energy at night, when it is least valuable to utilities buying the power, but this one will catch the predictable, strong breezes that come up every sunny summer afternoon, he said, when the sun heats the land more than the sea, creating an onshore breeze.

Over a year, onshore machines in the Eastern United States produce only about a third as much electricity as would result if they ran at full tilt every hour of the year, but this one will produce 40 percent to 50 percent as much, he said, because winds offshore are stronger.