The Napa County Sheriff’s Office is seeking the public’s help in its effort to determine exactly what happened Saturday when a Glen Ellen man apparently drowned after he was ejected from his speedboat on Lake Berryessa.

“All appearances is it was a boating mishap, but it’s our job to be skeptical,” said Napa Sheriff’s Capt. Doug Pike. “There were two other people on the boat that day. It’s not that we think they’re not telling us the truth, but until we locate a body or determine if there was some sort of mechanical failure or other reason to explain what occurred, we will continue to investigate.”

Roger “Deets” Winslow, 49, a father of three and popular high school wrestling coach, was behind the wheel of his performance speedboat with two passengers on board. Somewhere along a section of Lake Berryessa called The Narrows, something caused the boat to rock suddenly in one direction and jerk back in another. The force threw Winslow over the side into the deep water, according to the Sheriff’s Office. When his passengers circled around to pick him up, they found signs that he may have been injured by the boat’s propeller. He is presumed to have drowned.

A search employing divers and an unmanned robot has not yet turned up any sign of Winslow, who has been described by friends and family as an expert boat pilot who was knowledgeable enough about his boats to be able to work on them himself.

Now, officials are seeking anyone who may have either witnessed the incident or seen Winslow’s boat beforehand. His passengers reported to authorities that the boat’s engines were making “knocking” sounds before it violently swerved in one direction and then back in the other.

It was the jerking that apparently ejected Winslow from the boat, they said.

Pike said they had not yet been able to determine if a mechanical issue caused the boat to malfunction. Alcohol was on the boat, he said, but they do not yet know if it played a role in the accident.

In asking for help from potential witnesses, sheriff’s officials have released a photo of Winslow’s boat, a vessel made by Southern California-based builder Eliminator, whose boats are used primarily for racing. His is white with a pickle-fork nose and was registered in Arizona. It has black flames along each side.

“We’re just trying to get any independent accounts, if there are any,” he said. “We just want to check all our boxes.”

Pike said the search for Winslow’s body was continuing and on Monday, they would use a side-scan sonar device that would be able to give them high-definition images of the body of the lake, which in The Narrows reaches depths of up to 170 feet. The device, he said, is being provided by the city of Santa Clara.

Anyone with information is asked to contact Sgt. Chris Carlisle at 253-4637.