Secrets of WTC Shipwreck Sleuthed Out

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Unraveling the mystery surrounding the shipwreck found last year during excavations of the World Trade Center site has resulted in several facts as well as theories. The 18th century vessel, likely a single-masted sloop, measured approximately 50 feet long, and had a shallow, double-ended draft aided by a small, tapered keel built of squared-off hickory that ran from stem-to-stern. The hull was built from Philadelphia oak trees — one of which had lived for at least 111 years and was still growing in 1773, its youngest sapwood preserved in one of the boat’s timbers.

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Maritime historian Norman Brouwer had suggested that the unusually crafted sailboat was from a small rural shipyard and the trees for its timber from the same forest. “The data we see suggest something very similar,” says Neil Pederson of the Lamont-Doherty Earth Observatory’s Tree Ring Lab in Palisades, NY. “It’s an interesting intersection in experts,” he told Discovery News. He was part of a four-person dendrochronology team from the Tree Ring Lab working on samples of the vessel’s white oak planks and its hickory keel. Other tree species used in the boat’s construction included spruce and southern yellow pine, reported wood deterioration researcher Robert Blanchette of the University of Minnesota.

Looking up tree ring patterns for white oak timber samples is like hunting down a family’s genealogy. To get the most accurate result, teams of people around the world need to have already done the manual labor of counting rings and entering forest timber chronologies into a database. Then it’s a matter of sleuthing through generations of tree life-cycles to find a pattern that fits: where the timber samples and the trees share the same local climate of wet and dry years allowing them to make matching patterns of wide rings and skinny rings. So where to start?

An oak sailboat in New York could have originated anywhere in Europe or North America. Dutch ships originally carried sloops across the Atlantic in the 1600s. Whose side was this sailboat on? Pederson said when they first heard of the find they weren’t sure if they could track the soggy wood – when the team saw the keelson, the upper floor of the hull, the planks looked like white oak. When Blanchette confirmed their suspicions but added that they’d be getting a sample of hickory from the keel, the tree-ring team were relieved. The hickory keel sample was key – “it’s been extinct in Europe for two million years or so,” Pederson said.

So once the team did their own grueling process of slowly drying the timbers, waiting to see if the wood would decay, then sanding the samples, and counting the rings, sometimes as thin as one thousandth of a millimeter, and hoping each sample would provide at least 100 years of rings to make the sample comparable to other chronologies then the scientists got started looking for a match. They used a computer system to compare their samples with chronologies of forests from the New York State’s Hudson Valley and then took a stab at a historical timber chronology they have from Philadelphia, “and that just about nailed it – really good,” said Pederson.

When the wreck was first found the archeologists were confused as to whether they were looking at the front (stem) or back (stern) of the vessel. Turns out the sloop was rounded at both ends. Last month the Port Authority of New York and New Jersey excavated behind a concrete wall, where archeologists from the firm AKRF hoped to find remnants from the bow, where the figurehead and bowsprit thrust forward over the curving stem, the part of the sailboat that forms a bowshock of cresting waves and a good place to look for dolphins when under sail.

Eventually AKRF did recover a large portion of the structural part of the front of the boat. Now that material is with the Center for Maritime Archaeology and Conservation at Texas A&M University, where Director Kevin Crisman and his team are assisting the excavators with storage of the timbers. Alum and archeologist Carrie Fulton, now at Cornell University, spent a week cleaning, inspecting, and recording the new finds using stereophotography to generate 3D models.

One image (right) shows part of the Roman numeral II, a draft mark carved into the lower stem indicating the point where the vessel was two feet from the bottom of the keel. With light loads this mark would likely hover just at the water line indicating to the crew that they would run aground if they traveled through water that was less than two feet deep, an event they likely did often.

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If the hull was part of the original vessel and not part of a refurbishment, the tree ring data point to a launch date for this shallow-sailing sloop that was sometime after the 1773 winter’s Tea Party in Boston, and likely before the signing of the Declaration of Independence on July 4, 1776, in the vessel’s hometown. This is a boat that sailed during the American Revolution with a crew that traded up and down the Hudson River goods, such as leather shoes, they had collected during several long bouts spent in the Caribbean. But the crew were a bit lousy (but, really, who wasn’t back then?) and, in its own way, so was the boat, having picked up tiny wood-boring Teredinidae mollusks, “the termites of the sea.” But as Kevin Eckelbarger of the University of Maine’s Darling Marine Center, who identified the shell morphology in the bored-out timbers, told Scientific American, “They are really aggressive. They make termites look like amateurs.”

Curiously, the shipbuilder had the luxury of installing expensive iron fasteners instead of the typical wooden trunnels or treenails common during that time. A luxury, because of the price of iron then, but also a labor-saving trick that actually made the sailboat more vulnerable to storm damage and leaks. Marine archeologist Warren Riess of the University of Maine told Discovery News that for most sailing vessels of this period, shipbuilders typically drilled a hole through both the exterior and interior oak planks framing a boat’s ribs and then pushed an octagonal trunnel, also made of oak, all the way through connecting both sets of planks. It was a labor intensive effort, but when the wooden planks expanded and contracted with changes in temperature the wooden trunnels did the same. Iron on the other hand was easier to install, but chewed through wooden hulls, perhaps just not as fast as the saltwater shipworms.

Riess speculates that the shipbuilder came into possession of the iron by chance, either from another “ship full of nails that came in from some place” needing fixing, or from iron captured during the revolution that made the metal suddenly cheap to buy.

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Which brings up the question of what the owner of the vessel thought when he bought it. And the captain’s intent and purpose during his command of the sail. The boat carried munitions, as would be expected. Other mercantile sloops of about the same size have storied histories serving on both sides of the Revolution. The single-masted sloop Katy, for example, was recommissioned in 1775 as the USS Providence, to clear out Tory vessels from New England colonial ports, sailed in and out of Philadelphia, and stormed British forts in Bermuda and the Bahamas, where her crew also helped in capturing two British sloops. The tables turned on August 14, 1779, in Penobscot Bay, now part of Maine, and the Providence crew scuttled their sailboat to keep her out of British hands.

One of the puzzle pieces into the history of the discovered World Trade Center vessel includes a pewter button with the number 52, a regiment of the British Army. Whether this is from a captured British soldier or something a superstitious sailor found remains unanswered. Perhaps the British were the last to claim the vessel. As Riess said, the British held New York City throughout the war, and evacuated in 1783 after the treaty in Paris. The last humans on the sailboat left it to sit on the shores of New York harbor where other occupants endemic to saltwater marshes such as horseshoe crabs, sponges, oysters, and snails made the oak planks home. AKRF ecologists even found the bones from a (now extinct) passenger pigeon – though the bones could have been leftovers from an earlier meal.

As Riess adds, “The vessel has been a puzzle since the beginning.” With its double rounded ends and shallow draft this vessel would have made for easy cargo transfers in bays, and beaches. “This was a shallow draft needed to get into shallow areas, typical to load and unload. The tide goes out and you throw a couple planks onto the mud or sand and unload,” he said. He offers several options for theories as to the purpose of the sailboat: although it may have been a simple grain or cargo vessel making trades up and down the Hudson River and between the Caribbean, perhaps it also peacefully helped ferry British soldiers out of New York City after the war, or maybe more notoriously the ship had a run-in with the Marsh Pirates of New Jersey.

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IMAGES:

The stern of the vessel during excavation of the World Trade Center site in 2010. (Courtesy Douglas Mackey).

Young sapwood in a sample of oak, the thick outer section of the tree where sap flows is an indication that this tree was likely felled during the last ring shown on the sample, which cross-dates to 1773, though the outer layer of bark is missing and the rings are extremely tight and difficult to count making it also possible that the tree was cut down in 1774 or 1775. (Courtesy Neil Pederson, LDEO Tree Ring Lab)

The keel was squared-off during its construction, making the last ring in the shargbark hickory sample which cross-dates to 1724 likely a ring closer to the heartwood of the tree. (Courtesy Neil Pederson, LDEO Tree Ring Lab)

A micrograph of the hickory keel in cross-section showing an “inside view” of the ship wood. (Credit: Joel Jurgens, University of Minnesota)

Stern timbers taken from the World Trade Center site were cared for at the Maryland Archaeological Conservation Laboratory until sent for analysis and storage at other labs. (Courtesy of the MAC Lab Facebook Page)

Carved Roman numerals in the stem of the vessel indicating draft marks. (Courtesy Carrie A. Fulton)

The reconstructed orlop or lower deck from the stern. The scale is in feet; the deck itself was just over 7 feet at its broadest. (Courtesy Carrie A. Fulton)

The Continental Sloop USS Providence by Alice B. Borsik. (Courtesy of the U.S. Naval Historical Center.)

Oil painting of by V. Zveg in 1973, depicting Continental Sailors and Marines landing on New Providence Island, Bahamas, on 3 March 1776. Their initial objective, Fort Montagu, is in the left distance. Close off shore are the small vessels used to transport the landing force to the vicinity of the beach. They are (from left to right): two captured sloops, schooner Wasp and sloop Providence. The other ships of the American squadron are visible in the distance. The operation was commanded by Commodore Esek Hopkins. (Courtesy of the U.S. Naval Historical Center.)

The 1969-launched single-masted shallow-draft sloop Clearwater, sailing up the Hudson River. The ship is the maiden vessel for the environmental organization: Hudson River Sloop Clearwater, Inc., based in Beacon, New York. (Wikimedia Commons)