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

[Castout]

Old Russian submarine propeller design

https://1drv.ms/i/s!Ag_CxMbMom_9h2733t0nKsoGzwB2

Old American submarine propeller design

https://1drv.ms/i/s!Ag_CxMbMom_9h29tNo2_jujBAP5G

The Russian design if I speculate correctly is meant to optimize speed for any given rotational speed of the propeller. This is achieved by pushing seawater outward on the propeller longitudinal tip which in turn will be pushed back by the propeller blades resulting in more water being pushed back generating more opposing force that propel the submarine forward.

The American design seems not as easy to guess because these kinds of stuff isn't my expertise. However, if I am to speculate, the ring is meant to prevent some seawater from being pushed outwardly by the tip of the propeller's blades. What this does is a bit unclear. One, it could be to maximize speed too by minimizing outwardly flow of propelled seawater. It could also to minimize cavitation by smoothing the flow direction of propelled water. It could also for both guesses. However, the ring seems very thin instead of elongated so it might very well be to minimize cavitation.

What do you think?

[FPSchazly]

I would not consider that particular Victor-III prop design to be an old design, I would consider this to be an old design (from Alfa):



I am by no means a propeller expert or fluid dynamics voodoo witch doctor, but the design referenced in your first link seems to decrease the pressure along the leading edges of the propeller blade in order to reduce cavitation.

As to the ring around LA props (which may be getting into classified territory ), I imagine it's also there as a form of cavitation reduction to reduce the prop tip cavitation. I read an article a while ago stating that there are three forms of propellor cavitation, and cavitation at the tip is one of them. It's where the blade is rotating the fastest, so tipping over the blades, like with that Victor-III prop, seemingly increases prop area without increasing the speed of the blade as much.

Anyone well-versed in propellers, please feel free to correct my terminology.

[Aktungbby]

The American design seems not as easy to guess because these kinds of stuff isn't my expertise. However, if I am to speculate, the ring is meant to prevent some seawater from being pushed outwardly by the tip of the propeller's blades. What this does is a bit unclear. One, it could be to maximize speed too by minimizing outwardly flow of propelled seawater. It could also to minimize cavitation by smoothing the flow direction of propelled water. It could also for both guesses. However, the ring seems very thin instead of elongated so it might very well be to minimize cavitation.

What do you think?

No! No! that's (ring) to keep mile-long seine/gill fishing nets from tangling the propeller.... often sinking the fishing boat. http://www.prop1.org/2000/accident/1989/890712a1.htm & http://www.dailymail.co.uk/news/article-3687891/Portuguese-submarine-caught-net-French-fishing-boat-English-coast.html http://news.nationalpost.com/news/world/fishing-boat-captain-says-a-russian-submarine-lurking-in-u-k-waters-snagged-his-net-and-nearly-dragged-him-under Seriously; it's a big problem for all submarine vs net fishing boats-there have been fatalities for years Look up "fishing boats snagged by submarines". It's really bad!

[FPSchazly]

Originally Posted by Aktungbby

No! No! that's (ring) to keep mile-long seine/gill fishing nets from tangling the propeller.... often sinking the fishing boat. http://www.prop1.org/2000/accident/1989/890712a1.htm & http://www.dailymail.co.uk/news/article-3687891/Portuguese-submarine-caught-net-French-fishing-boat-English-coast.html http://news.nationalpost.com/news/world/fishing-boat-captain-says-a-russian-submarine-lurking-in-u-k-waters-snagged-his-net-and-nearly-dragged-him-under Seriously; it's a big problem for all submarine vs net fishing boats-there have been fatalities for years Look up "fishing boats snagged by submarines". It's really bad!

Ah yes, that makes a lot of sense. At one point in time, I had considered it was to keep the towed from getting snagged in the propeller, as well.

[Aktungbby]

I was being humorus U were right the first time! Subs don't give a bilgerats ass about fishing boats...that's just 'collatertal damage'. Although I'd imagine getting tangled in a net causes 'cavitaion' too!http://www.globalsecurity.org/military/systems/ship/systems/shrouded-propulsor.htm

A shrouded propulsor (not a 'ringed propeller') is a directional collar around the submarine's propeller. It lowers the passive sonar signature of the sub and provides improvement over exposed propeller designs in both efficiency. The Improved Los Angeles (SSN-751 onwards) have a shrouded propulsor, as do all subsequent classes of American attack submarines. At least one Russian KILO has had its propeller replaced by a shrouded propulsor, which is now used by new US and British nuclear submarines. A shrouded propulsor is identical to a standard shafted propeller, with a cylindrical ring of metal attached at the the tips of the propeller blades around the full circumference....Improved design in submarine screws (propellers) significantly reduces cavitation. Cavitation is reduced by the shroud, as the duct maintains higher pressure around the blade tips and prevents cavitation bubbles from forming. One method of improving the efficiency of propellers uses a pipe shroud to encase the propeller. This shroud or nozzle forces more of the water directly out from the propeller. And by ducting water flow through the shroud, tip vortices can be harnessed to provide thrust.

[FPSchazly]

Originally Posted by Aktungbby

I was being humorus U were right the first time! Subs don't give a bilgerats ass about fishing boats...that's just 'collatertal damage'. Although I'd imagine getting tangled in a net causes 'cavitaion' too!http://www.globalsecurity.org/military/systems/ship/systems/shrouded-propulsor.htm

Oh, very good haha you got me there. That was some straight faced dead-pan there!

[Castout]

Originally Posted by FPSchazly

I would not consider that particular Victor-III prop design to be an old design, I would consider this to be an old design (from Alfa):



I am by no means a propeller expert or fluid dynamics voodoo witch doctor, but the design referenced in your first link seems to decrease the pressure along the leading edges of the propeller blade in order to reduce cavitation.

As to the ring around LA props (which may be getting into classified territory ), I imagine it's also there as a form of cavitation reduction to reduce the prop tip cavitation. I read an article a while ago stating that there are three forms of propellor cavitation, and cavitation at the tip is one of them. It's where the blade is rotating the fastest, so tipping over the blades, like with that Victor-III prop, seemingly increases prop area without increasing the speed of the blade as much.

Anyone well-versed in propellers, please feel free to correct my terminology.

Oh so both are meant to reduce cavitation?

I wonder how effective is the Los Angeles propeller design as the ring is very thin......

For the Russian propeller, yes it can be argued it is to reduce cavitation too I guess but at the same time I think it increases the amount of water being pushed by the propeller thus increasing its speed efficiency.

[Kapitan]

If they left these on i wonder how much extra noise there would be ?

especially as this submarine has a top speed of 44.7 knots i could imagine it being like a freight train running past a house and with these left on even louder.





And this is the back end of the K222 project 661 Anchar and still holds the fastest sustained underwater speed record (Alfa could only sprint not sustain)
Considered the predecessor to Charlie I and Alfa this boat had a titanium hull armed with 10 SS-N-7 ASM she like Charlie and Oscar are one shot wonders.

The boat was out of comission in 1988 and scrapped at zerverodorchka in 2010

[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

[NiceSub]

Originally Posted by FPSchazly

I would not consider that particular Victor-III prop design to be an old design, I would consider this to be an old design (from Alfa):



I am by no means a propeller expert or fluid dynamics voodoo witch doctor, but the design referenced in your first link seems to decrease the pressure along the leading edges of the propeller blade in order to reduce cavitation.

As to the ring around LA props (which may be getting into classified territory ), I imagine it's also there as a form of cavitation reduction to reduce the prop tip cavitation. I read an article a while ago stating that there are three forms of propellor cavitation, and cavitation at the tip is one of them. It's where the blade is rotating the fastest, so tipping over the blades, like with that Victor-III prop, seemingly increases prop area without increasing the speed of the blade as much.

Anyone well-versed in propellers, please feel free to correct my terminology.

What are those small propellers next to the large one? What is their task?

[Castout]

Originally Posted by NiceSub

What are those small propellers next to the large one? What is their task?

That's for extra quiet operation at very low speeds like 1-2 knots I think or not more than 3 knots. They might even use battery to reduce noise but I'm not sure.


@Speed150mph

The thin ring on the 688i might not be effective at high speeds just as you mentioned.

The Russian Typhoon SSBN has very long rings (shrouds) which is to say that they are to prevent cavitation by the propellers' blade tips to higher speeds than on the 688i, probably even to its maximum speed...But the tips of those blades are 'sloppy'. Perhaps because they have those long rings/shrouds and they thought to give the blades maximum push efficiency.

The thing with propellers is that they don't push with equal/uniform force distribution....I guess that's why everyone is building submarines with pump-jet propulsions to have a more uniform force distribution to minimize cavitation...allowing for higher tactical speed.

A more uniform force distribution demands a new innovative way to propel submarines without the use of any propellers or to use much thinner and more numerous blades perhaps not unlike blades in jet engines...

Perhaps, although this is just speculation, a new innovative way to propel submarines can be found by mimicking nature. There's a reason propeller- like propulsion isn't found in nature. It could be because it's not the best way to move around underwater...

Edit:
I googled octopus inspired submarines and found a good link.
http://www.ibtimes.com.au/octopus-in...e-ever-1419803

[Kapitan]

I think what you find is that the Russians went for speed in their submarines not so much stealth, the Americans went for lower speeds but more emphasis of being quiet.

If you look at the designs From the Thresher permit class forwards you notice this here is a submarines that has substantial speed of around 30 knots yet at the slow end they are a lot quieter than the Russian boats.

Prop design has a lot to do with this, if you look above the Romeo has twin 4 blade screws which would make a racket at any speed, and the counter rotating screws i don't think give much more quieting effect and likely cause pressure waves between the blades thus creating a slight noise increase in that area.

Americans / West have always tried to out do in terms of quality the Russians knew they couldn't match the tech platform to platform so created a wide range of measures to defeat the technology advances of the west.

None are more prevalent than a lone Project 877V Boat assigned to the black sea fleet in Sevastopol, here is a submarine that steps outside the idea of "good enough" and opens a new door the results of the trails are still classified the submarine is still active it was launched in 1990 and forms along side her newer and more advanced project 636 sisters the back bone of the submarine fleet in the black sea.

Alrosa is one of a kind submarine she is fitted with a pump jet propulsor almost like a mini jet engine if you would, its unclear how much noise reduction you get out of the modification but i would guess as they have not fitted it to newer boats or new builds including the Lada class that this trials boat wasn't too successful some pictures illustrate the system in bits and pieces.

























Taken from a screen grap but this is what type of screw the Project 877 and 636 boats have normally and infact still use