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Imagine putting together a giant complicated puzzle with half the pieces misses. This is what nautical archaeologists must do. Even the smallest, seemingly insignificant object is an integral part of the puzzle. When all pieces are in place archaeologists are able to establish who the ship was, where it came from and how it sank.
Once a ship goes down it gradually begins to decay. Over the years, exposed wood disintegrates or is consumed by sea worms. Metals corrode and are covered by concretion. Soon silt, sand and mud pile up, concealing the vessel below the surface of the seabed. Finding an intact old ship on the seabed is almost impossible. This is why every shred of wood is looked upon as being as valuable as a gold coin. Unlike commercial treasure hunters, the only wealth nautical archaeologist are seeking is information.
When diving, nautical archaeologists wear a special watertight neoprene suit. Sometimes they also wear 20 kilos (48 pounds) of lead weights. Pressure changes under water are more obvious at a depth of less than 10 meters (30 feet) than at greater depths. What is more, disparity in pressure is even more detectable within the first 3 meters (10 feet). Pressure changes also affect a divers ears and they must constantly adjust to these changes, even when they shift up or down no more than a foot or two. Divers must also make adjustments with the tide because this cause water pressure to change as well.
Water temperature presents another important challenge for nautical archaeologists. Archaeological work involves a great deal of mapping, photographing and measuring, tasks necessitating that the diver remain motionless for long periods and although divers wear watertight suits, the numbing cold soon starts to effect them, making it more difficult for them to complete detailed tasks.
Frequently visibility conditions are extremely poor if not zero. Under these conditions nautical archaeologists search by touch rather than eyesight. In sand and silt even the presence and movements of the other divers make an already poor situation worse by stirring up the sediment and further obscuring the artifacts.