thanks Dr bill!
its not just the noise... propeller blades cut into the water and smooth thin, shaper blades use less energy to acheive the same ammount of movement. (just as thin pointed hulls on ships cut through the water faster)

the noise, (cavitation) is partly caused by bubble breaking (just as a SST leaves a sonic boom, the propeller leaves a vacuum as it screws it way through the water.. and the results is bubble formation..)
so making a 'quiter' propeller, (which makes it harder to find and track a ship at sea) also make the propeller more effecient (so submarines can go farther between re-fueling and retooling)



my other obsession