Let's talk about [old] submarine propeller designs (nothing confidential)

[speed150mph]

I believe they hit the nail on the head. The ring on the 688 prop is most likely for reducing blade tip cavitation noise at slow to moderate speeds. This feature is what gives the 688 class it's somewhat higher silent speed. The Russians main focus with propeller design was speed first and foremost, and ducting the propellers on the diesel boats like the tango was more for protection when operating in shallow water then silencing. We are only now seeing the use of pump jets coming into Russian designs, such as the Borie and the Yasen-m class subs.

In response to the fella who brought up the Alrosa, she was a test bed for pump jets on diesel electric subs. Now pump jets are very effective at dampening noise and cavitation at moderate speeds, but only have a marginal effectiveness at slow crawling speeds. This makes them rather useless on conventional diesel electrics like the kilo as they are generally quiet enough on battery to avoid detection, and more importantly, they are pretty well forced to operate at slow speeds to have adequate range on their batteries.

As mentioned the pump jet comes into it's own at moderate speeds, which diesel patrol subs hardy ever operate at. The Russians deemed it to not be work the higher costs to install it on the subs for so little reward which is the reason why they didn't continue with it. They no doubt however worked the design into their SSN and SSBN designs, since they can operate at the moderate speeds where pump jets become most efficient without worrying about battery life.

[Aktungbby]

http://americanhistory.si.edu/subs/anglesdangles/taming6.html

The tactical speed of a submarine is that speed at which the submarine is quiet enough to remain undetected while tracking enemy submarines effectively, with sources of self-noise reduced to the point that other submarines and ships can be detected using onboard passive sonar sensors. The the maximum burst speed of a submarine is the highest speed that can be achieved by the submarine's propulsion system, regardless of the self-noise created in the process. In the past, the tactical speed of a submarine was typically significantly less than its burst speed, though in the case of the SSN-21 Seawolf it is said that the tactical speed of 25 knots is a significant fraction of the burst speed of the boat.

https://fas.org/man/dod-101/sys/ship/deep.htm Shrouded propulsors are good; Depth is better! The Best Depth for a submarine to avoid detection by a hull-mounted sonar is conventionally regarded as the Sonic Layer Depth plus 100 meters

[Kapitan]

Originally Posted by speed150mph

I believe they hit the nail on the head. The ring on the 688 prop is most likely for reducing blade tip cavitation noise at slow to moderate speeds. This feature is what gives the 688 class it's somewhat higher silent speed. The Russians main focus with propeller design was speed first and foremost, and ducting the propellers on the diesel boats like the tango was more for protection when operating in shallow water then silencing. We are only now seeing the use of pump jets coming into Russian designs, such as the Borie and the Yasen-m class subs.

In response to the fella who brought up the Alrosa, she was a test bed for pump jets on diesel electric subs. Now pump jets are very effective at dampening noise and cavitation at moderate speeds, but only have a marginal effectiveness at slow crawling speeds. This makes them rather useless on conventional diesel electrics like the kilo as they are generally quiet enough on battery to avoid detection, and more importantly, they are pretty well forced to operate at slow speeds to have adequate range on their batteries.

As mentioned the pump jet comes into it's own at moderate speeds, which diesel patrol subs hardy ever operate at. The Russians deemed it to not be work the higher costs to install it on the subs for so little reward which is the reason why they didn't continue with it. They no doubt however worked the design into their SSN and SSBN designs, since they can operate at the moderate speeds where pump jets become most efficient without worrying about battery life.

Which sounds about right to be honest it doesnt give much reward but on something like borei and yasen it would indeed be a good reward

this post i put the pictures up of the arse end of alrosa

http://www.subsim.com/radioroom/showthread.php?t=229270