KEY LARGO -- Long before GPS, the coral reef tract that runs along the Florida Keys routinely sank unsuspecting ships. Storms also blew boats into the hard, shallow structures, contributing to a massive underwater graveyard.

An American schooner named Kate, the British brig Lion and the French ship Cora Nelly all met their demise on this popular marine trade route. So did the Spanish warship Arcuana and the Winchester, a British man-of-war captained by John Soule that hit a reef so hard it tore a hole in its hull in 1695.

“It’s a fascinating world out there of all the shipwrecks in our own backyard,” says Brenda Altmeier, a support specialist for maritime heritage resources at the Florida Keys National Marine Sanctuary.

Some shipwreck sites have been well known for decades. The Winchester was discovered in 1938 and was the subject of a National Geographic article. But the whereabouts of many of the sunken vessels — or what little is likely left of them — remains a mystery.

Key Largo-based ocean explorer Ian Koblick and his partner Craig Mullen are hoping to change that by conducting the first comprehensive survey of the Keys ocean floor.

“We’re treasure hunting for cultural jewels,” Mullen says.

They began by dusting off a 1988 report by researcher Judy Halas, who spent endless hours scouring 18 volumes of admiralty records, newspaper articles and other sources to document 877 ships that were lost, bilged, saved, sunk, rammed, stranded, “ashore” or torpedoed in the waters of the island chain.

Koblick and Mullen are attacking the shipwreck project with technology — sidescan sonar, subfloor profiler, magnetometer, remote-operated vehicle (ROV) — along with their decades of expedition and underwater experience.

Koblick was an aquanaut with the Tektite undersea research program off the Virgin Islands, searched for treasure with Mel Fisher and co-developed the Jules Undersea Lodge in Key Largo. Mullen, a former Navy diver, was president of the company that helped recover the booster rocket after the space shuttle Challenger exploded over the Atlantic.

Since 2003, their Aurora Special Purpose Trust has discovered 27 wrecks, from a seventh century B.C. Phoenician vessel to a World War II submarine, in the depths of the Mediterranean.

Turning their attention to their own backyard, they don’t expect to find intact wrecks or cargo. For starters, many of the ships were made of wood, “and the wood is all gone,” Mullen says. “Critters like the shipworm eat it up.”

Much of the cargo and other valuables was recovered by Keys “wreckers” who scavenged the wrecks, and much of the rest became divers’ souvenirs. But Koblick and Mullen believe there is still a good chance of locating cannons, steam boilers, machinery and other metallic parts.

They began by surveying two sections of the Upper Keys off Key Largo with a sidescan sonar that looks like a torpedo and has been nicknamed “The Fish.”

One stretch, which includes popular dive site Molasses Reef, is seven miles long by half a mile wide and runs between 60 and nearly 200 feet deep. The other half-mile-wide swatch is about 11 miles long, running from The Elbow to Turtle Reef, and includes Carysfort Reef, where three dozen ships are documented to have run into trouble.

The data was captured onboard the 34-foot survey vessel by Rick Horgan, a remote sensing specialist and former Navy buddy of Mullen’s, and also transmitted to Horgan’s computer via the tow cable.