Quote:
aken from Vepr157's amazing prop album:
http://imgur.com/a/IQBOiIt is a nice collection of photos. One error which could affect model building is that the photo of Scamp's five bladed screw is printed in reverse. This is from the Friedman book and was printed with the negative reversed. The blades should be pitched so that the screw turns clockwise when viewed from behind the boat.
The explanation of the noise caused by the original Scamp screw (water boiling and cavitation) is also incorrect. The original five bladed screw had problems with "blade rate" noise, which is a low frequency emission caused by the large flat blade entering and exiting the disturbed wake caused the rudder and stern planes. The individual blades abruptly entered the disturbed wake and vibrated. This low frequency sound carried great distances in the deep sound channel. The skewed back propellers had dampening features (pure Wasatch sand in their hollow shafts), smaller surfaces (hence 7 blades instead of 5) and entered and exited the wake more gradually due to their shape. SOSUS hydrophone arrays were placed in the deep sound channel, and could pick up Soviet subs (which lacked the 7 blade, damped propellers) often at great distances.
The George Washington (SSBN 598) originally went to sea with a five bladed propeller, and it is said that SOSUS could track the Washington during transit to Holy Loch, Scotland from Groton.