Pump jets,Attenuators, and the hole... - Technical question

[wayne frey]

Question.
On the Russian boats, many have attenuators on the hub.
This, as I understand, is to thwart wake homing torpedos.
Ok, so if pumpjets are all about stealth,would an attenuator be worthwile?
How about the one picture of the Kilo with the pumpjet on the internet? It seems to have a hole, or dimple in the cone. I take it that is for collapsing any bubbles converging on the cone. Am I right?
Kinda theory type questions. Thought I would wake the board up a little.
How about it Steve?

[gerwalk]

Question.
On the Russian boats, many

Question.
On the Russian boats, many have attenuators on the hub.
This, as I understand, is to thwart wake homing torpedos.
Ok, so if pumpjets are all about stealth,would an attenuator be worthwile?
How about the one picture of the Kilo with the pumpjet on the internet? It seems to have a hole, or dimple in the cone. I take it that is for collapsing any bubbles converging on the cone. Am I right?
Kinda theory type questions. Thought I would wake the board up a little.
How about it Steve?

Good question Wayne!
I wonder if their real use is "to thwart wake homing torpedos". A friend of mine reffers to them as Grimm wheels which are Relative Rotational Efficiency Devices (i.e. they improve thrust of the props. I think they do so by converting part of the rotational energy of the wake by redirecting the flow) Even the Queen Elizabeth 2 used to have these devices and in that case I'm sure they were not intended to thwart torps!! (they were removed since the blades tend to break and produced more trouble than expected)

I would like to know more about these things!!

[wayne frey]

Interesting.
If attenuators improve thrust

Interesting.
If attenuators improve thrust ?, why do we not use them? I am sure the engineers at Electric Boat did not miss that.
Am I right about the hole in the hub too?
It seems like the pumpjets would be the most advanced design possible.Even if they do seem to effect turning radius

[gerwalk]

Interesting.
If attenuators improve thrust

Interesting.
If attenuators improve thrust ?, why do we not use them? I am sure the engineers at Electric Boat did not miss that.
Am I right about the hole in the hub too?
It seems like the pumpjets would be the most advanced design possible.Even if they do seem to effect turning radius

[color=#000000]Well, there is that famous pic of a 688 with an "attenuator" attached to the prop.

As for the pump jet]

[anonymous]

http://www.la-ex.org/View_Photos/1999_WESTPAC/1999_WESTPAC_Clear_waters_HMAS/WP99_Clear_Water_of_HMAS_Stirling_400.jpg


Steve...you mean me?

Several things may




Steve...you mean me?

Several things may be going on here in this discussion. Russian, American and others have used attenuators in some fashion. Most are to create a low pressure area behind the propeller hub to reduce as much as possible wake which homing torpedoes zero in on, as well as just detection of the sub in the first place. These types of homing torpedoes (primarily Russian) do this by zig zagging behind through the wake of the target (sub or surface vessel) back and forth sensing the turbulence created by the propellers and hull as it moves threw the sea. Homing in on the stern. Much the same in principle but not in movement to the way a IR Sidewinder air to air missile corkscrews as it flies toward it's target, creating a wider aperture or field of view for the IR sensor in the nose to acquire the target. A wake homing torpedo zig zags to the target, a missile cork screws. Navy surface vessels and many other Navies tow a 'Nixie' or other decoy as a torpedo counter measure.

A hollow point on the British PJ's do the same function, reducing or collapsing the prop wake and the associated turbulence.

637 class subs all used an abbreviated dunce cap, but included a bowl or bell shape attached to the end, this to enhance the low pressure area behind it. The 594 class appears to not have used these, but the 585 boats later did.

The 688's seem to use several kinds of props, the standard skew back seven blade with a second set of eleven small rectangular blades attached, all turning in the same direction. See above image, from the USS Los Angeles 688 home page site...Sterling Australia...1999. These maybe used by the earlier 688's (to non-688I's) retrofitted. A slightly smaller diameter version without the eleven attenuators and a coke bottle shaped dunce cap use a ring on the circumference of the prop. These are used by the 688I's. This ring protects the delicate blades (both physically and with no damage.....acoustically too) from ice, and facilitates recovering more thrust at the blade tips where props are usually less efficient. A poor mans PJ. The performance is about the same for either prop used. The technique for making these ringed props used on 688I's were first developed on the 637 class boats, but I do not think this was standard equipment. The vortex attenuators on the non-688I boats....also act as a kind of screen acoustically too. Enemy sonars trying to ID the vessel and attempting to determine the vessels speed by getting a blade count might have a harder time with seven plus the eleven additional blades. The Ohio's have been reported to use such attenuators on their props too. There could be other props we are likely not aware of too. I have no evidence of this, but keep in my mind the option open. Part of the fun researching such subjects.

The Navy is still sensitive about these things. Recently a friend displayed his Thor 688I at the Groton Museum. His model came back fine minus it's ringed prop (provided standard in the Thor kit) after its tenure on display. An Admiral visiting the museum had a fit, and the model prop was returned crushed. This is another reason why when building models of modern subs....I tend to build models of foreign submarines. I would hate to have to kill an Admiral for busting my sub model. Being how valuable Admirals usually are. LOL.

Ethically we are responsible as accurate scale modelers when presenting models of modern American submarines to the public .....to both protect our nation and our sub crews as well as to enlighten and enjoy. Does this mean no ringed props? I think ring props on 688 kits are okay in this case. These kits have been around for some time now. Any photos of a 688I launching will easily show the ring prop outline, drawing attention to those in the know, always covered in red, white, and blue canvas. I am sure the Chinese and Russians know just as much, likely more. Can they mill such technology though? Likely not yet.....well the Chinese any ways. But recently the Chinese Navy has been giving us some surprises with new classes of submarines appearing far ahead of intelligence time window projections. I know the Chinese and the Royal Navy monitor this web site. At one time, the Chinese blocked the subcommittee site to their internet servers. When explained this was a hobby site, the Chinese removed the 'block' several years ago.

Steve



Edited By Dolphin on 1118849061

[petn7]

that's some nice information there!

that's some nice information there!

[wayne frey]

Thanks Steve,
I knew this

Thanks Steve,
I knew this link would be too tempting for you]http://www.subcommittee.com/forum/icon_smile.gif[/img], Remeber?

[anonymous]

I know what you are

I know what you are driving at Wayne. I do not know that.

Steve

[gerwalk]

Thanks Steve,
I can't believe such

Thanks Steve,
I can't believe such stupidity and rudeness from an admiral! Rest assured that the chinese or else knew about ringed props for long time before Thor strated making his models! The admiral's act implies that the american public, the ones who pay taxes to make those subs, don´t have the right to know about it...

[PaulC]

I know it sounds silly

I know it sounds silly from our point of view, but I can understand the response. While submariners realize that foreign countries are always on the lookout for US sub secrets, they are going to do whatever they can within their power (emphasis on "within their power") to prevent such secrets/info being disseminated.

I've had conversations with subvets at fun runs who would not give general geographic locations regarding incidents which were 50 years old. Would telling me where his boat was back then compromise a boat today? No. But again, that is the mindset of the Silent Service (he also related how upsetting it is to see similar details broadcast freely on cable history channels).

On a similar note, when I was aboard USS Helena for a DVE in March 2001 members of the wardroom related their frustration in having to follow orders to give Chinese dignitaries the VIP treatment during a WestPac the previous summer. Tour of the boat, angles and dangles, simulated attack, the works -- all as a gesture of goodwill in a pre-9-11 world.

[anonymous]

Interesting thread. There have been

Interesting thread. There have been a number of recent articles in the New London Day about the future of the Submarine Force (catalyzed by both the threat of closing the New London Sub Base and the the annual Submarine Review Meetings held last week in Virginia). One senior Submarine admiral stressed that with the current 54 submarines, he couldn't cover all the tasking requests, yet the Navy is talking about drawing the force down to possibly 37 hulls. In the meantime, the Virginias are running $2 billion plus per hull (action figures not included), and being built at one per year. Let's see 30 year hull life, one build per year, you can do the math.... Another article yesterday focused on the fact that no current submarine design work is going on, and the skilled engineers who design submarines are dwindling faster than new ones are trained. So, the picture for the future is not very bright, yet there is clear evidence that the need for submarines may grow substantially with new types of threats and foreign submarines.

I think that it may be high time for the submarine force return to loosening up a bit on promoting themselves to the public. Make no mistake, technical secrets and the security of current operations still have to be maintained. However, many of us saw a more open face to the sub force pre 9-11, after the end of the Cold War. The SubCommittee was welcomed onto the New London Base and treated to tours of the boats, including the brand new Seawolf. (BTW, submarine models (WITH ringed propellers) were at those regattas! No one reported any crushed propellers). I think the submarine force would do itself a world of good by describing some of the operations carried out during the Cold War. Certainly selected operations carried out in the 1950's, 60's, and 70's could be revealed. Blind Man's Bluff and other books have already opened that door a crack. I hate to say it, but in the present environment, the Sub Force needs to make the case to the public that it is a worthwhile investment. That means telling a good story about some past accomplishments. By continuing to hold to Tradition and being the "Silent Service", the Submarine Force could well become the "Silent Extinct Service". I sure don't want to see that....

[anonymous]

Na, I don't blame the

Na, I don't blame the Admiral who ever he/she was.....they error on the side of caution doing this. It was perhaps an over reaction though. They are doing their duty in their minds. They (the silent service) are most unaware that in the public (we 'outsiders') have access to a cornucopia of (some what) timely information, the information revolution called this Internet. The barrier of security and reasonable precaution maybe a two way street. We can't see inside understandably, but they may not be occasionally looking out either. To this admiral obviously, the only SubCommittee he/she likely had ever heard of was a congressional one. LOL.

In the Virginia class boats...the Navy already has an excellent design for the current needs now, just more are need to be authorized, I would like us to run out of 'State' names. A projected force of 60 boats....SSN, SSGN, SSBN. The Navy needs more subs...period. The issue in Iraq needs to be made certain, there are ominous issues with North Korea, China/Taiwan, perhaps Iran that need our vigil too. Worried about funding....in the 60's Vietnam was a drain of funds to the sub force....a few boats went long between maintenance periods.....one of those was USS Scorpion. It is a different situation now.....or is it?

I did hear somewhere of a follow on to the Ohio SSBN design. A design based possibly on a Virginia design. But there is so much in this post - cold war...post 9/11 world to consider.

Steve



Edited By Dolphin on 1118970187

[gerwalk]

Interesting thread indeed!]

[color=#000000]Interesting thread indeed!]

[anonymous]

I do not know about

I do not know about the thrust attenuators enhancing performance, I just know they do not inhibit performance. In model performance, it is a waste of time deweling on attentuators for performance considerations...spliting hairs here. On our little models, attenuators or not, it makes no difference running them, only for scale points in a model judge's eye.

My avatar is from a photo I took of an Israeli Dolphin submarine model prop I made several years ago. It is really a modern German prop design. I made it out of brass from scratch. No...I do not make props as a regular habit, so no requests please. I am glad to help with research where I can, but I want to finish my model projects for a change.

Steve



Edited By Dolphin on 1118967299

[anonymous]

Na, I don't blame the

Na, I don't blame the Admiral who ever he/she was.....they error on the side of caution doing this. It was perhaps an over reaction though.
Steve

No, Steve, I'm sorry but I disagree. If the story is correct, someone was kind enough to LEND their submarine model to the museum for display. Presumably someone in authority from the museum also approved of the display. If an Admiral thought that the model disclosed features that were questionable, the proper response is to immediately remove it from public viewing and ask the individual to retrieve their model. They might ask at that point how they came about modeling the particular feature in question (in this case, it's a commercial model kit). I don't think the proper response is to smash the object and then return it. That's not a behaviour I would expect from any adult. It also did not really get to the bottom of the question as to how the model came to have that feature.