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.
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.
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.
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.
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.
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.
Much of nautical history rests on jamming a squared peg into a round hole.