“In deciding which technology and methods would work best in the search for Kormoran and Sydney I never had any doubts that the correct tool to use was a deeptow side-scan sonar. This technology had been pioneered in the 1980's and it was ideal for locating lost shipwrecks in the deep ocean, especially when the area to be searched was large. I had used this type of sonar in the past to locate much deeper shipwrecks, including Lucona, Derbyshire and Hood, as well as the SS Rio Grande, a German blockade runner that Blue Water Recoveries found at the mind-boggling depth of 5,762 metres and in doing so was awarded a Guinness World Record for discovering the world's deepest shipwreck. Nevertheless, while depth was a factor in our choice of equipment, it was actually the combination of extreme depth plus the enormous search area that made the search for Kormoran and Sydney a perfect candidate for using this rather unique search tool........In its most general form a sonar can be thought of as a powerful underwater flashlight that uses sound waves, instead of light, to image objects on the seabed. Specifically, a side-scan sonar is one that is towed at the end of a long steel cable connected to a survey ship and can scan the seabed to either side of the ship's track to create a coherent two-dimensional map of the surface and objects lying upon it. Under the watchful eye of a skilled expert viewing and interpreting the sonar images as they are created in real time, a side-scan sonar is the surest way to detect shipwrecks whether their hulls are intact or shattered and even when the surrounding seabed is complicated by rugged geological formations.
A deeptow side-scan sonar is simply one that can operate very deeply, to a maximum of 6,000 metres (3.25 nautical miles).”
David goes on to explain that this sonar needs to be towed at great depths in order to obtain acoustic shadows, which “can tell us a great deal of information about the height and shape of the object, especially as the basic two-dimensional nature of a sonar image means that an object's height is not directly apparent in the image and has to be inferred.” The particular sonar he used for this venture to locate Sydney and Kormoran was the SM-30 side-scan sonar from Williamson & Associates, pictured above from page 124 of the book. If you'd like to learn more about the capabilities of this sonar, check out the web site: http://www.wassoc.com/Upload/Specifications/sm30.pdf
If I get really lucky, some day I'll get to see this piece of equipment in action as it locates the debris field and wreck of the USS Strong DD 467. Until then, I'll continue to learn what I can about what it will take to get us there.