Warwick lies, torn asunder, on the floor of Castle Harbour. As we slowly uncover the ship’s buried skeleton, we are continuously astounded by the quality of her construction. She was built from densely packed, massive oak timbers. Between three layers of outer planking, frames, and inner planking (confusingly referred to as ceiling), Warwick’s hull would have been solid wood, two feet thick in places. It is incredible to contemplate the forces required to rip her apart, and partly explains why a large section of her starboard side is still intact and well preserved.
Timber remains, as seen through a fish-eye lens.Treenails are visible protruding from the frames. In the upper left corner you can see a line where the a frame once continued. – © 2012 Warwick Project}
Seventeenth Century English vessels were held together with heavy wooden pegs called treenails (pronounced truhn-el, as in trunnel). You can see them sticking up out of the frames where the planking has come away. Where only outer planking remains, you determine the position of frames by looking for rows of treenails.
A loose treenail, rescued from the site – © 2012 Warwick Project
Treenails are powerful, rust free fasteners. A carpenter would first drill a hole through an outer plank, the frame and an inner plank. They then drove a long, tapered wooden peg (the treenail) into the hole as far as it would go and cut off the protruding ends. When immersed in water, the treenails expand and lock in place, sandwiching the frames and planks together.
Hull planking, with visible treenails securing the planks to the frames – © 2012 Warwick Project
Most of the treenails we find on Warwick were roughly octagonal, instead of being round like a dowel. They could be carved quickly, and their angular surface bit into the sides of the round hole.
A treenail’s roughly octagonal shape (only 7 facets are visible), viewed from the end – © 2012 Warwick Project
Often, carpenters split the end of the treenail with a wooden wedge, driving the sides apart and locking it firmly in the hole. It is very difficult to see these wedged treenails under water. You have to carefully look for changes in the grain to identify the wedge – though sometimes you are lucky, and dust fills in the minute cracks, rendering them visible.
A treenail with a uncharacteristically visible wedge – © 2012 Warwick Project
Treenails provide crucial clues for nautical archaeologists. They can tell us how the ship was built, and if she had been repaired – critical to understanding her use, age and history.
Doug and Piotr – gently coerced into posing with a relatively boring, stubby treenail for this post. – © 2012 Warwick Project
Much of nautical history rests on jamming a squared peg into a round hole.
– Doug
Warwick, 1619: Shipwreck Excavation 
Reblogged this on Diving | Archaeology.
Great to read and see the pictures!
Can you explain briefly on what aspect of the treenail indicates if the ship has been repaired? Is it the location, wood the specific treenail is made of, etc?
Great question!
Sometimes repairs are obvious. They might be fastened differently, a different type of wood, or cut across several planks. Most are more subtle , and treenails can help identify them. Wedging is a good clue. Carpenters either used a square peg, wedge or crossed wedge to expand the head of a treenail and lock it in place. The style that was used depended on the situation, and where the shipwright was from.
To determine where repairs are, you have to understand the construction sequence first. When you see a treenail driven through the center of a second treenail, you know that one was in place before the other. This might mean that one layer of planking was attached to the frames, and then a second, or it might mean that they decided to put in a second fastener. It might also indicate a later repair. It could be many things.
The same is true if you find cut off treenails beneath the ceiling (inner) planking. If the shipwright fastened the ship’s outer planking first, they would have to cut off the protruding treenail ends before laying the inner planking. In other circumstances it might indicate a repair, where ceiling planking was removed, protruding heads adzed flat, and new plank put in place.
In almost all circumstances, you have to look at a broad range of data, think about the construction sequence and look for things that are out of place. On the other hand, if you are an expert like Jon Adams or Kevin Crisman, you just look at it and know.
Hope this helps (and sorry for the delay)
Doug