SAN FRANCISCO – Poor seamanship, including risky or inattentive sailing maneuvers, was primarily to blame for two yacht racing crashes in April that killed nine mariners off the California coast, yachting association investigators have found.

Examinations conducted of both accidents, which occurred two weeks apart, were presented on Thursday at a San Francisco conference of U.S. Sailing, the chief organizational body for American sport and recreational yachting.

Reporting for the first time on the wreck of the 37-foot (11.3-meter) yacht Aegean, whose entire four-member crew perished, investigators concluded the vessel slammed into a small island off the coast near the California-Mexico border because of “an inadequate lookout.”

The investigative panel stopped short of saying the skipper of the Aegean might have fallen asleep but concluded the vessel was on autopilot at the time of the April 28 accident.

The Aegean, which was racing from Newport Beach, California, to Ensenada, Mexico, had abruptly vanished from satellite tracking, and a subsequent U.S. Coast Guard search found bodies and debris.

It was unclear at first whether the boat had run aground or collided with a larger ship, but a GPS record tracing the yacht’s path later showed it sailing straight toward an island.

“Because we don’t have any survivors or eyewitnesses, we don’t have any understanding of why they hit the island,” Bruce Brown, head of the investigating panel, told sailors gathered for the conference. “We believe there was an inadequate lookout. We found nothing that led us to believe there was an attempt to prevent a collision.”

Navigational missteps were already cited for a separate accident two weeks earlier in which five sailors aboard the 38-foot (11.6-meter) yacht Low Speed Chase died while competing in the Full Crew Farallones Race off the coast of San Francisco.

Investigators faulted the boat’s captain for charting an unsafe course that took the vessel too close to a rocky island adjacent to shallow waters and large, breaking waves.

Addressing the conference on Thursday, Sally Honey, head of the panel examining that April 14 crash, called it “a failure of seamanship.” And she dismissed suggestions that a rogue wave hitting the Low Speed Chase sealed its doom. “They could have and should have known not to be in that spot,” she said.

Pilots should use maps and charts showing islands like the ones both boats hit to steer clear of them, Brown added.

“We as mariners need to pay close attention that we consider hazards and obstructions on charts as things we should avoid, not to see how close we should come,” he said.

The investigators also found that none of the four Aegean crew members wore flotation devices, though autopsies showed at least two of them had died of blunt-force trauma. Some of the sailors killed in the crash of the Low Speed Chase likewise wore inadequate safety gear.

(Editing by Steve Gorman and Lisa Shumaker)