Forty boats sped off silently Monday in what is billed as the world's largest race for solar-powered watercraft. High winds capsized several...

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LEEUWARDEN, Netherlands — Forty boats sped off silently Monday in what is billed as the world’s largest race for solar-powered watercraft.

High winds capsized several boats during a time-trial qualifying round Sunday, and technical problems with the launching crane pushed back Monday’s start. But all 40 qualifiers finally departed under fair skies, spokeswoman Christel Pieper of the Frisian Solar Challenge said.

The six-day race covers a 135-mile course in the north of the Netherlands. Speed limits on narrow waterways have been temporarily waived for the boats, the fastest of which can go nearly 19 mph.

Sunlight is not the most obvious source of renewable energy in the rain-soaked Netherlands, but organizers say the threat of poor weather will spark creative design.

Participants met that challenge with technologies that included water-cooled solar cells, carbon-fiber propellers and mathematically optimized designs to reduce drag.

The Technical University of Delft, which won last year’s event, has outfitted its boat with gallium-arsenide solar panels, and the hull was professionally engineered by the Marin Research Institute Netherlands. The craft weighs less than 200 pounds without the skipper.

Delft also is a perennially strong contender in a similar solar-car race in Australia.

Competitors include technical students just out of high school, doctoral students, and even independently wealthy hobbyists.

“Our secret weapon is our propeller,” Joop Steenman, a private enthusiast, said of his large, yellow boat. Its precisely engineered carbon-fiber blades cost $8,500.

Steenman, the owner of a gas-turbine company, said he spent $186,000 on his boat, which is shaped like an aircraft carrier and has a single hull and a large deck covered with a thin layer of black solar cells. The cells can generate a combined 1.6 kilowatts under ideal conditions, Steenman said.