Looking for a spot to pick a tomato or cucumber while learning about ecological sustainability?

Then head for New York City’s unique floating farm, the Science Barge, now moored off Riverside Park near West 70th Street. The small-scale model farm, open for public and educational tours, delivers a powerful and optimistic environmental message: that the city can grow its own food using local renewable resources.

The Science Barge is the first major project of NY Sun Works, a nonprofit engineering firm, founded by Ted Caplow, 37, an Upper West Side resident. When Caplow graduated from Harvard 15 years ago with a degree in sociology and a burning, but unfocused, desire to save the world, he planned to enter the Peace Corps. But he didn’t want to teach English, and the organization’s other option – beekeeping – was unfamiliar territory. Somewhat disheartened, he returned to school and studied engineering at both Princeton and Columbia, while still mulling over what he could do to save the planet.

In 2005, Caplow visited a hydroponic greenhouse in Ohio where plants grew in nutrient-enriched water. “I was blown away when I saw that food could be produced in a scientific and efficient way,” Caplow said. He spent the next two years turning this epiphany into the reality of the Science Barge, which was launched on May 4 off West 44th Street. After its stay off West 70th Street, the barge will be moved to Stuyvesant Cove Park on Sept.6 and remain open this year until Oct. 31.

The heart of the Science Barge lies in its small hydroponic greenhouse where tomatoes, peppers, cucumbers, lettuce and herbs are nurtured in water, rather than soil. Most of the plants are trained to climb vertically to conserve space, and they thrive under ideal, computer- controlled temperature, humidity and fertilizer conditions. The cucumber plants grow six inches daily. On a late spring day, the greenhouse yielded 70 cucumbers, 36 heads of lettuce and several bunches of cilantro. With the help of the barge’s staff, visitors currently harvest and take home all the produce grown on the model farm, but discussions are underway with city food distribution agencies to handle any future excess.

Although only 1,300 square feet in size, the barge’s small greenhouse can grow enough vegetables for 25 people, using seven times less land and four times less water than conventional agriculture. The barge also generates its own power, mostly solar, and does not discharge any pollutants into the environment.

“The Science Barge is a crucible for visualizing the city of the future,” wrote the University of Vermont ecologist and engineer John Todd in an e-mail. “Its internal life support systems tap renewable energy, purify air, restore purity to water and feed people, all at the same time.”

Caplow has estimated that New York City could use its existing flat rooftop space to grow enough vegetables to feed all of its eight million residents, if the city adopted the technology and methods showcased on the Science Barge. The barge purifies Hudson River water and collects rainfall to irrigate its plants and cool the greenhouse. Two large solar panels mounted on the barge meet its energy requirements, and they are backed up by five wind turbines as well as a generator that runs on waste vegetable oil collected from restaurants, if the sky is overcast for several consecutive days.

The carefully integrated systems of the Science Barge took six months to build. “The design is working the way it’s supposed to,” Caplow said with satisfaction.

He is delighted by the reception the Science Barge’s integrative approach to technology, agriculture and education has received from the public, schools and city government. “People love plants and hunger for a closer connection with nature, even in a very urban environment like New York City,” Caplow said. Inspired by the Science Barge, a public school in Washington Heights is considering the installation of a hydroponic greenhouse on its roof to help its students reconnect with nature and learn about sustainable urban agriculture.

“The Science Barge is helping New Yorkers understand the choices we all need to make to ensure that New York is not only the greatest city on Earth, but also the most livable. It’s a fantastic addition to our waterfront,” e-mailed Manhattan Borough President Scott Stringer about the prototype.

The barge’s message of ecological sustainability is also timely. Mayor Michael R. Bloomberg’s PlaNYC 2030 commission’s projected recently that New York City’s population will increase by one million residents over the next 25 years. Referring to this prediction at the barge’s launch in May, Jeffrey Sachs, director of the Earth Institute at Columbia University, said, “Learning to manage our natural resources and, in particular, our renewable resources will be essential if we’re going to get through this very difficult phase ahead.”