The 16-foot, 1965 Atlas boat overturned between the Estero Americano and Doran Beach north of Bodega Bay, said Sgt. Ed Hoener of the sheriff's office's Marine Safety and Enforcement Unit.
It is believed Silveira, a Sacramento resident, was out crabbing, Hoener said. He was seen leaving the Bodega Bay Harbor earlier in the afternoon, Hoener said.
A woman saw Silveira in distress just inside the surf line off Pinnacle Gulch Beach. He was seen paddling the boat and signaling for help by waving the paddle in the air, Hoener said. She ran home and called 911, Hoener said.
At the time of the call, the wind was blowing at 10 to 25 knots from the southwest and waves were 11 feet high, Hoener said. The water temperature was 52 degrees and the air temperature was 46 degrees and a small craft warning was posted at the Bodega Bay Coast Guard Station, he said.
The Coast Guard responded but did not see anyone in the water, Petty Officer Erik Watson said.
The sheriff's office's helicopter Henry-1 was called around 4 p.m. and spotted Silveira in the water about 150 feet offshore, sheriff's Sgt. Dave Thompson said.
The helicopter crew used a long-line to recover Silveira and flew him to shore where he was pronounced dead, Thompson said.
Silveira had a second house in Sonoma County, Hoener said.