Tiny sailboats rocked from side to side Sunday morning along the Petaluma River, at the mercy of the momentary wind gusts. “Any wind is good,” George Pedrick, 65, who lives in Point Richmond, said.

For a few hours most Saturdays, a handful of skippers carefully steer yachts across Louisville’s Harper Lake. Though they behave similarly to full size sailboats, the yachts are about 3 feet long — ...