Eric Schmitt, captain of the 44-foot treasure-hunting boat Aarrr Booty, went into the water not expecting to find much. He had no idea what was waiting for him at just 15 feet.

“We were only three days into our hunting season,” says Schmitt. “We’ve found washers and dryers and even cars by this site — to find the treasure only 15 feet underwater was really unbelievable.”

In the 1960s Schmitt’s father started diving the wrecks off Fort Pierce, Florida, recovering thousands of silver coins. Following in his father’s footsteps, Eric began hunting the same wrecks a few years ago, using mapping software to determine where to find the booty. Schmitt’s family, having searched through the shipwrecks of the 1715 Spanish fleet since 2011, cheered him on as he brought the first of the 52 small gold coins to the surface. And although all the coins are valuable, there was one in the pile worth more than all of them combined — the Tricentennial Royal.

“This coin is one of the rarest in the world, with only one or two ever found,” says Schmitt. “It wasn’t used for currency. It was a presentation piece that would have been personally delivered to King Phillip V.”

The coin is worth $500,000 and was in U.S. Federal Court custody until the end of 2015; it’s expected the Schmitts will sell it to a private collector for up to $1 million.

“While some people might say we’re lucky, it was really a lot of hard work,” says Schmitt. “This business has peaks and valleys, but treasure hunting is our dream — and there’s still $400 million worth of stuff down there waiting to be found.”