Why Navies Around The World Keep Submarine Propeller Designs So Secretive
Arthur T Knackerbracket writes:
https://www.slashgear.com/2208743/why-navy-submarine-propeller-designs-are-kept-secret/
Militaries around the world frequently release photographs and videos of submarines entering or leaving port. Yet if you look closely at them, one detail is typically missing: the propeller.
[...] At first glance, a submarine propeller may not seem all that different from one found on a commercial ship. However, every aspect of its design is carefully engineered to help the vessel move as quietly as possible through the water. Put another way, naval propeller design places stealth above propeller efficiency. Stealth is achieved by minimizing cavitation, which is the sudden implosion of vapor bubbles when the speed of propeller blades drops local water pressure below its vapor point, creating an acoustic signature that can be tracked by the enemy. Details such as the number of blades, their shape, curvature, pitch, and even the precision with which they are manufactured all influence the amount of noise and vibration produced as the submarine travels beneath the surface. While those differences may appear subtle to the casual observer, they can have a significant impact on a submarine's ability to remain hidden during operations.
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