In the clear blue water 150 feet down, off Palemano Point on Hawai'i's Big Island, Rick Rogers swam along the ocean floor, concentrating on the light white swirls of staghorn reef below him.

As tiny bubbles of air escaped from his tank, his black flippers propelled him above the coral, next to schools of reddish mempache and juicy turquoise uhu fish. The scene was breathtaking, but Rogers didn't care about nature. He was looking for manmade objects only: porcelain plates, pieces of cannons, a sunken iron anchor.

Finding evidence of a shipwreck beneath the ocean would finally prove a theory that Rogers, an amateur historian, has been promoting for decades. He thinks a handful of Spanish and Dutch ships visited Hawai'i in the centuries before Captain Cook landed there in 1778. Some Europeans came ashore after shipwrecks, like the characters in "The Swiss Family Robinson," he claims, and eventually integrated into the local society. That early European influence in the 16th and 17th centuries forever changed Hawaiian culture, Rogers says.

"It's cool — you read 'Swiss Family Robinson' and pirate stories, and here it really did happen," said Rogers, a retired commercial airline pilot. "But nobody else is really paying attention to it."

To prove his theory, Rogers has spent countless hours poring over ancient maps, tracking down artifacts in the dusty storage rooms of disorganized museums and combing Hawai'i's jagged coastline. The one-time Army salvage diver has done much of his work off the Pilialoha, a baby-blue Navy launch he bought in 1986 and loaded with equipment and maps, as well as an assortment of sleeping bags and cushions.

He's battled historians and archaeologists — most with many more degrees on their walls than he has — who say he has no proof to back up his theory. They, like the history books, stick to the idea that Cook was the first European to step onto Hawai'i, two centuries after Rogers thinks other Europeans landed here. Some politely concede his version of history could have happened, but that there's no proof. Others are more blunt.

No Europeans contributed to Hawaiian culture before Cook, Thomas S. Dye, a professional archaeologist, said, adding: "I don't think Rick's work is worth a story."

Rogers thinks the proof is obvious. He's found maps from as early as 1589 that show islands in Hawai'i's shape and location, albeit with different names. Hawaiians had iron when Cook arrived, although they had no evident means with which to produce it, indicating that Europeans had already brought it. Europeans also brought diseases prior to Cook's landing, Rogers says: Remains of a young woman who died in 1664 indicate she had congenital syphilis.

The dive off Palemano Point was a search for irrefutable evidence: a wrecked Spanish galleon. Between 1565 and 1815, Spain ran a main trade route between Manila and Acapulco, passing near Hawai'i. Five ships disappeared in that period, and Rogers thinks two of them wrecked off the coast of Hawai'i and that some people made it ashore.

Though he defended his theory in an in-flight magazine of a now-defunct airline, Rogers has been rejected by most other publishers. In 1999, he self-published a book about his search, "Shipwrecks of Hawai'i: A Maritime History of the Big Island."

He says he'll keep going back to Palemano Point off the coast of the Big Island, hoping that a storm or quake will stir up the evidence that will prove him right.