[swdw]

Originally Posted by Capt Jack Harkness

Well, how about this: "submarine cavitation, which is relatively slight in shallow water, can be almost completely eliminated in deeper water." - Naval Maritime Forecast Center/Joint Typhoon Warning Center

Sigh, this is true under normal operating conditions but does not apply to large changes in prop speed in relation to the hull speed when doing things like taking evasive action. A knuckle in the water is created by a combination of prop cavitation and cavitation off the control surfaces due to a high speed underwater turn. It can even be heard on passive sonar because of the noise being created by the bubbles collapsing.

By the way, does anyone have an idea what the cavitation really looked like on both the three- and four-bladed props on our fleet boats during normal cruising both surfaced and submerged?

There shouldn't be any visible when "normal" cruising submerged. Cavitation creates noise as you mentioned so submarines try to keep away from it. Controlled changes in bell speed help reduce the chance of cavitation.