Have you ever wondered why most navies cover the propellers of their new submarines while awaiting launch?
Simple: Acoustic profiling.
You see, naval engineering is such a well understood science, a naval engineer can, with relative ease and relying on both technology and experience, determine the underwater acoustic resonance of a propeller while in movement simply by looking how the blades are shaped and how many are integrated into the design, enabling the profiling of the boat into a database to allow easier detection by passive sonar, since you no longer need to discriminate from normal underwater sounds to detect a submarine, and instead can simply look for a known frequency, making detection far easier for an enemy navy.
That’s why is highly surprising when in an official photoshoot navy/dock personnel completely fail to cover up the propeller, since all the design effort that goes into a propeller, almost all of it focused on making its detection harder, is thrown into the trash the moment you allow it to be photographed, like what the germans did recently with their newest Type 212 sumarine
Of course, many old submarines don’t abide to these rules, mainly because they use old propeller designs that are so well researched it’s just not worth it to cover them up.
Or simply because the propellers are so damn dirty it’s difficult to properly gauge how their design works.
Of course, detecting an modern submarine sailing underwater is still the hardest thing any navy can set itself to do nowadays, regardless of what they know or don’t know about the shape of a propeller, but anything than can help make this monumental task easier is extremely welcomed, so handing it over in such seemly innocent way is something professional navies USUALLY strive to never do.
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