Search for sunken 16th century ship
Inductive reasoning. It's what detectives use to work backwards from evidence at a crime scene to develop a chronology of events that, with luck and diligence, will lead to a suspect.
It's also the modus operandi for Portola Valley resident and geophysicist Sheldon Breiner and a team of archaeologists and a historian who meet periodically along the Mexican coast of Baja California. They're investigating the disappearance of a Spanish galleon believed to be the San Felipe.
The San Felipe left China in 1576 headed for Acapulco by way of Manila with a cargo that included silk, beeswax and tons of Ming Dynasty porcelain. Records show the details of the cargo but not the San Felipe's arrival at its destination, and the Spanish were meticulous with their records, Mr. Breiner says in an interview.
Mr. Breiner spoke about this exploratory adventure at Portola Valley's Historic Schoolhouse on Nov. 16. The town's Nature & Science Committee sponsored the free event and about 20 people showed up.
Shipments of porcelain left China for Spain twice a year for some 250 years starting in 1565, Mr. Breiner says. There is debris indicating that the 100-foot, 400-ton San Felipe may have run aground off the desert coast of Baja.
Lying on and under the shifting sands of this corner of Mexico's Sonoran Desert are about 1,000 artifacts. While the researchers haven't yet found any silk, which would have been encased in wax, they have found beeswax, some lead sheeting used on the hulls of 16th century ships to discourage underwater pests, and a great many pieces of porcelain scattered along a two-mile-long line in the sand, Mr. Breiner says.
Why might the ship have grounded? Strong prevailing winds, scurvy among the crew of 200, a need for food or water, or a new mast or spar — the reasons are not known. Had the ship reached Acapulco, its cargo would have been offloaded and hauled overland to the Gulf of Mexico and then shipped to Spain, a two-year to three-year trip altogether, Mr. Breiner says.
With hundreds of thousands of years of predictable winds, waves and depositions of sand as reference points, the line of debris is readable. The team has worked backward from the locations of these artifacts to place the likely remains of the sunken hull. After scanning the area with an ultra sensitive magnetometer, the team now has tracking data showing magnetic anomalies consistent with a buried hull. In short, they have a strong suspicion as to where it is.
If this anomaly is a sunken galleon, it may never be known for certain whether it is the San Felipe. Ship owners back then did not paint names on hulls, Mr. Breiner says. The porcelain can be dated by experts skilled at matching a design with the year in which that design was current.
Mr. Breiner says he plans to return to the site in February to survey the wreckage in detail and create a grid-based map of the debris field. The magnetometer can detect ballast stones, cannon barrels, and iron spikes used to hold the ship's ribs to its keel. Other items with a smaller footprint but still detectable include weapons, tools, boxes, furniture parts and personal effects of the crew. The lack of oxygen under the sediment inhibits corrosion.
Team members, when they do speak about this project, hold back its exact location. Search and recovery work is undertaken only with the explicit permission of the Mexican government and in the presence of archaeologists from the INAH, the National Institute of Anthropology and History, Mr. Breiner says.
Once Mexican specialists isolate and recover the hull and debris, the pieces will be restored to the extent possible — perhaps a five-year enterprise — and displayed in a museum in Ensenada, the capital of Baja California, Mr. Breiner says.
The joy of a journey like this one, Mr. Breiner says, is that it takes on a breadth of field of its own. Geology, oceanography and map-making are as critical as magnetism in solving this puzzle.
The questions Mr. Breiner poses in a paper on the subject are many. Why is the line of debris so straight? Why are there more objects at the southern end? How do the answers to these questions help reconstruct the events of the shipwreck? Where are the ship's anchors and why are they where they are? What has happened to the hull over four centuries? How did the porcelain stay in relatively good condition for hundreds of years in such a sandy and abrasive environment?
"There's a lot of information that can come from a well understood search and study of an ancient ship," Mr. Breiner says.
Finding buried objects
One piece of equipment Mr. Breiner has not used and that wouldn't do much good in this exploration is a metal detector. That device transmits an electrical signal; if something metal is within range, the transmitted signal creates within the metal an electrical current detectable by the device.
The magnetometer, by contrast, is passive. It senses the Earth's magnetic field, which is present everywhere all the time. The device notes anomalies in that field caused by materials that have or do not have magnetic properties.
Airport and courtroom devices that screen for metal objects on a person are magnetometers that can sense a belt buckle's disturbance to the planet's magnetic field. The device in use by Mr. Breiner in Baja is thousands of times more sensitive.
At the shipwreck, grains of magnetic minerals in the sand will provide a uniform background noise, Mr. Breiner says. Any interruption in that noise, such as would be made by a buried nonmagnetic pile of wood and ceramics, will indicate its presence by the absence of that background noise.