Wreck diving and an interest in maritime history go hand in hand. While most of us dive on well documented wrecks, there's always the chance that we may someday have the opportunity to dive an unknown wreck, or even learn new things about a wreck that has already been explored at length. Here, we'll take a look into the way explorers make the discoveries they share with the rest of us.
Propulsion Systems
You can tell a lot about a wreck's history, just by taking a look at its propulsion system, which is often one of the very last things to go as a wreck decays. Many historic vessels were steam powered, so taking a look at the boilers usually yields important clues. How many boilers were on board, and how were they arranged? Have they shifted at all? Finally, were the boilers welded, or were they riveted into place? Older ships were put together with rivets.
In the case of wrecks where engines are present, they are usually aft of the boilers if the ship was steam powered; if the ship was diesel powered, there might be stacks of batteries around. Recording information about a wreck's engines can provide plenty of insight . Look to see how many cylinders each engine has, and look for the gears that lead the way to the propeller shaft, too.
On single shaft ships, propeller shafts exit the hull where it narrows at the stern, and on those with double shafts, there could be two narrow sections or a single narrow section; these areas tend to be the strongest and often outlast other portions of the hull. When you get to the propellers themselves, look to see how many blades they have. A prop with four blades likely belonged to a merchant ship or other slow-moving vessel, while a propeller with three blades usually belonged to a warship. Manufacturer information is often stamped on propeller blades; on iron blades, concretion can destroy this information, but on bronze blades, it is usually identifiable, providing important clues as to the ship's identity.
Rudder and steering systems also provide valuable insight; those with more than a single rudder were built for greater maneuverability. If you're looking at a wreck with multiple props and multiple rudders, you are probably at the site of a sunken ferry or warship - the rest of the boat's construction will give up more clues.
Hulls and Fittings
The way a hull is built can provide valuable information about a ship's origins and it can help us determine how best to navigate the wreck. The more you learn about shipbuilding, the better your likelihood of making a positive identification will be.
Helms, Steering Systems, and More
The ship's helm or steering binnacle will be attached to a number of different mechanisms that can provide insight, and steering systems are quite often fitted with maker's plates that bear identification information and sometimes even provide the ship's name. Winches, anchors, and masts can provide even more information; be sure to document everything as you explore.
The discovery of guns and other armament can provide even more information regarding the wreck's origin, and if you are able to gain access to the ship's holds and inspect the cargo, or look into berthing compartments, you may find even more clues. Look for refrigeration equipment, and look at galley and head fittings to see whether you can find clues. Navigational instruments are also identified with manufacturer information in most cases.
Finally, don't overlook little odds and ends; buttons, personal items, log books, and other valuable identifiers are often buried in debris. Don't forget to measure the wreck by laying a line and putting a knot in the line at the end; you can make an accurate measurement back up topside. If a ship is broken up, you may only be able to accurately measure the beam, but this can still provide valuable information.
Once back on shore, you can begin sleuthing in earnest. There are normally local records about ships that have gone down, so check libraries, and don't forget to investigate online. Remember, all this will probably take multiple dives; be sure to make good notes regarding position, and remember to document everything with photos if possible.