USS Seawolf- a propulsion question

Factual Questions
1

Ok, for any of you technology loving patriotic folk out there I have a question and some random musings. The USS Seawolf (SSN-21) is supposed to be ultra quiet and a super efficient killer. I remember pics from its commissioning and was interested that the lower mid section was draped in a giant white tarp with Old Glory emblazoned across it. One knows that when the military covers something up (figuratively or otherwise) that is the most interesting place to look.

My best friend is a nuke tech on a boomer sub and talks of the ‘mystery prop system under the tarp’ with awe and glee. As I was reading “Blind Man’s Bluff” about our Cold War Sub antics, it occurred to me that the system under the tarp may be some twist on the principle whereas water in one section of a looped system of pipes is heated the water begins to rise compared to the cooler water in a different part of the same system. This creates a flow of water sans mechanical pump.

Now that I have looked at some of the info online concerning the Seawolf it appears the sub is capable of great quiet and great (for a sub) speed.
So it seems that my ‘idea’ as to how one may get a super quiet flow of water (the heated water flow previously mentioned) with which to (possibly) propel the sub would not be sufficient to reach the 25 knot speeds often mentioned with the Seawolf. So in short, is my idea completely wacko? Could you get anywhere near the force needed to push this hulk with just the force produced with the heated water system? What system (generally speaking) does the Seawolf use to move fast and quiet? Or, have we just continued to improve prop design such as to further the anti-cavitation etc?

2

A nuclear plant would certainly make a lot of heat.

Worth noting that this isn’t the same thing as a magnetohydrodynamic (MHD) or caterpillar drive, which uses lots of magnetism and electricity to move water.

3

[QUOTE=Chouinard Fan]
water in one section of a looped system of pipes is heated the water begins to rise compared to the cooler water in a different part of the same system. This creates a flow of water sans mechanical pump.
[/QUOTE]

One of the things that makes the Ohio class SSBNs so quiet is the ability to run without the reactor cooling pumps, just using natural bouyancy of the heated reactor cooling water to circulate itself. (Not for propulsion, however.) If I understand correctly, the Seawolf is made larger in diameter such that it can fit a reactor plant of similar operation to that of the Ohio boats - the LA class is too skinny to fit one. Natural circulation is not good for full power, but apparently it will propel the Seawolf to 25 knots according to your wiki link.

If the Seawolf were electric drive (which some of the newer surface ships are, and I thought I read about the Seawolf too), then you get rid of another big source of noise, which is from the large bull gear that reduces turbine output RPMs to propeller shaft RPM.

The reason that they hide the propeller when surfaced or in dry-dock is to hide how many blades and what the blade pitch is. With that information, it is possible to deduce what speed the sub is making (if it were possible to hear the screw). The number of blades can help you determine RPM, and the pitch would then allow prediction of forward speed.

4

[QUOTE=Schuyler]
If the Seawolf were electric drive (which some of the newer surface ships are, and I thought I read about the Seawolf too), then you get rid of another big source of noise, which is from the large bull gear that reduces turbine output RPMs to propeller shaft RPM.
[/QUOTE]

It appears that I was incorrect on the electric drive for the Seawolf (see here or here). However, apparently they use a “pumpjet” which is conceptually like a ski-boat’s jet-drive. One benefit is probably that it contains cavitation noise within the duct.

5

[QUOTE=Schuyler]
It appears that I was incorrect on the electric drive for the Seawolf (see here or here). However, apparently they use a “pumpjet” which is conceptually like a ski-boat’s jet-drive. One benefit is probably that it contains cavitation noise within the duct.
[/QUOTE]

Thanks for the links; they were much better than what I had found. I do still wonder a couple things…

Although one always likes the thought of it in one sense, are we really going to use a large attack sub to insert SEALs to an AO? As a ground pounder I don’t know too much about squid things but it seems that the larger the craft the more depth required to hide it, the more costly it is if lost, and the less it will actually be used. It seems a lot like the soccer mom’s saying my SUV has a 4 in. lift, push button lockers, etc etc. when we all know the BMW is NEVER going to be taken more than 40 ft. up a snowy drive way. (I recall Rickover didn’t let his first nuke subs go on real missions for a long time, too risky for the PR program if lost)

When the wasp waist is mentioned I get the general idea (having seen rough schematics online before) but is this some sort of ball and socket joint allowing the vessel to pivot at its midpoint and thus turn better etc? Or, is this merely in reference to one layer of the sub’s shell tapering down to allow space for dive stations etc underneath the external shell of the sub?

As for the pump jet, it seems rather obvious from the pics in your link that the shroud is a permanent design feature and not used merely to hide the previously mentioned info concerning the prop. (Which seems to answer my question that no, we have not really come up with a new prop system we have just continued to improve the traditional screw prop to new heights [or depths…])

Now another thought that strikes me, does the shroud around the prop flex/move to direct the flow like a jet ski? This sort of thrust vectoring, F-22 style, would seem to make the thing turn like no sub in history.

6

A slight sidetrack, Chouinard Fan: Does your Dopername refer to the wine?

7

[QUOTE=Chouinard Fan]

Although one always likes the thought of it in one sense, are we really going to use a large attack sub to insert SEALs to an AO? As a ground pounder I don’t know too much about squid things but it seems that the larger the craft the more depth required to hide it, the more costly it is if lost, and the less it will actually be used. It seems a lot like the soccer mom’s saying my SUV has a 4 in. lift, push button lockers, etc etc. when we all know the BMW is NEVER going to be taken more than 40 ft. up a snowy drive way. (I recall Rickover didn’t let his first nuke subs go on real missions for a long time, too risky for the PR program if lost)

[/QUOTE]
The Los Angeles 688 class attack sub is indeed used as a launch platform for the Advanced Seal Delivery Vehicle.

8

[QUOTE=InvisibleWombat]
A slight sidetrack, Chouinard Fan: Does your Dopername refer to the wine?
[/QUOTE]

No in fact my username refers to Yvon. His influence on outdoor sports in general and rock climbing in specific have been tremendous. He made countless gear inventions and inovations leading, over the last 50 years, to the new BD cams that make me wish for the day when the yee ones grow up and I can give them my current climbing rack and buy me new Camalots. He changed the rock climbing world forever when he printed Doug Robinson’s article ‘The Whole Art of Natural Protection’ in the Chouinard Equipment Catalog, 1972 that ended the heyday of piton craft and led to the sustainable ‘clean climbing’ that we still enjoy today.

9

[QUOTE=UncleRojelio]
The Los Angeles 688 class attack sub is indeed used as a launch platform for the Advanced Seal Delivery Vehicle.
[/QUOTE]

Oh, and better than that, three of the ever larger Ohio class SSBN ballistic missle boats have been (or are being) converted into SSGNs. The SSGNs provide the ability to carry the Seal Delivery Vehicle and two of the tubes previously used to house nuclear missles are converted to carry SEAL team gear.

10

Yeah I wonder what genoius dreamed this up? Using a $3 billion sub to deliver 5 commandos to some 3rd world hellhole? This is what happens when the military needs to come up with a use for something they have bought. It reminds me of the Army’s Bradley Fighting Vehicle-it isn’t a tank, it isn’t an APC-its something in between and costs a lot of money.

11

[QUOTE=UncleRojelio]
The Los Angeles 688 class attack sub is indeed used as a launch platform for the Advanced Seal Delivery Vehicle.
[/QUOTE]

My first thought is: ‘Well sure they will be mothballing the things soon and using them for target practice!’
And then I realize, well you know, the idea of a sub surfacing to pick up distressed SEALs off the coast of Lebenon is not realisitic (like in Navy Seals). I guess these guys can sit ~20km off the coast, launch the guys and loiter for the pick up. No need to go ‘brown water.’

12

[QUOTE=ralph124c]
Yeah I wonder what genius dreamed this up? Using a $3 billion sub to deliver 5 commandos to some 3rd world hellhole? This is what happens when the military needs to come up with a use for something they have bought. It reminds me of the Army’s Bradley Fighting Vehicle-it isn’t a tank, it isn’t an APC-its something in between and costs a lot of money.
[/QUOTE]

Are you kidding? If the Brad is expensive then you need to think about dropping the pay for your elected officials (or the A.F. or Navy budgets). I had 10 M2A2 Brad’s, 11 M113 APC’s, 20 HMMWV’s etc. (as many vehicles as a battalion normally) and it still only came to $50 mil and that’s including all of the weapons, wrenchs, computers, and repair parts etc. that go to make them all work, and maintain them.
Basically a little bit of money (for the fed) for a whole lot of combat power.

If you are remembering The Pentegon Wars with Dr. Frasier Crane then, yes, be a critic of the Brad, but from first hand knowledge it is just like the M-16. Sure it started off poorly, but boy doesn’t it kill efficiently now?

Should I even mention that we got our $3 billion out of the Ohio’s when the USSR collapsed and that reusing them now is actually a efficient cost savings?

13

[QUOTE=Chouinard Fan]
(I recall Rickover didn’t let his first nuke subs go on real missions for a long time, too risky for the PR program if lost)
[/QUOTE]

Cite, please? And while you’re at it, define “real missions.”

The USS Nautilus (SSN-571) was commissioned in September 1954. She was “underway on nuclear power” in January 1955 and crossed the North Pole in 1958.

According to Wikipedia, “By 1962 the U.S. Navy had 26 nuclear submarines operational and 30 under construction.”

[QUOTE=Chouinard Fan]
When the wasp waist is mentioned I get the general idea (having seen rough schematics online before) but is this some sort of ball and socket joint allowing the vessel to pivot at its midpoint and thus turn better etc?
[/QUOTE]

Uh, no. :rolleyes: I don’t think you are grasping the mechanics of a 9,000 ton vessel.

[QUOTE=Chouinard Fan]
Or, is this merely in reference to one layer of the sub’s shell tapering down to allow space for dive stations etc underneath the external shell of the sub?
[/quote]

That’s more like it. That interior shell is referred to as the “pressure hull.” And it only applies to the USS Jimmy Carter (SSN-23).

[QUOTE=Chouinard Fan]
As for the pump jet, it seems rather obvious from the pics in your link that the shroud is a permanent design feature and not used merely to hide the previously mentioned info concerning the prop. (Which seems to answer my question that no, we have not really come up with a new prop system we have just continued to improve the traditional screw prop to new heights [or depths…])

Now another thought that strikes me, does the shroud around the prop flex/move to direct the flow like a jet ski? This sort of thrust vectoring, F-22 style, would seem to make the thing turn like no sub in history.
[/QUOTE]

No comment.

[Maverick]It’s classified. I could tell you, but then I’d have to kill you.[/Maverick]

I actually laid eyes on the Seawolf’s propulsor while she was still in the shipyard.

14

[QUOTE=Chouinard Fan]
When the wasp waist is mentioned I get the general idea (having seen rough schematics online before) but is this some sort of ball and socket joint allowing the vessel to pivot at its midpoint and thus turn better etc? Or, is this merely in reference to one layer of the sub’s shell tapering down to allow space for dive stations etc underneath the external shell of the sub?
[/QUOTE]

Wiki has this to say:

[QUOTE=wiki]
Carter is roughly 100 feet (30 m) longer than the other two ships of her class. This is due to the insertion of a section known as the Multi-Mission Platform (MMP), which allows launch and recovery of ROVs and Navy SEAL forces. The plug features a fairing over a wasp-waist shaped passageway allowing crew to pass between the fore and aft sections of the hull while providing a space to store ROVs and special equipment that may need to launch and recover from the submarine.
[/QUOTE]

[QUOTE=Chouinard Fan]
does the shroud around the prop flex/move to direct the flow like a jet ski? This sort of thrust vectoring, F-22 style, would seem to make the thing turn like no sub in history.
[/QUOTE]

Here’s a picture. I would be very surprised if that shroud pivoted for increased maneuverability. First, that would be moving a lot of metal around - have you seen the size of the prop on one of these things? Second, there are clearly vertical and horizontal control surfaces to provide directional control. Third, if I remember correctly, subs typically have a lateral thruster to increase maneuverability when going slowly/stopped - this allows the sub to yaw when there isn’t enough flow over the rudder to turn. And pitch can be controlled by ballast. Good questions.

15

[QUOTE=robby]
Cite, please? And while you’re at it, define “real missions.”.
[/QUOTE]
cite would be ~pg 186 of Blind Man’s Bluff that states that Rickover (as he did until he was 82) kept a very tight hold on his SSN’s and didnt let them on real missions. As you stated:
[QUOTE=robby]
The USS Nautilus (SSN-571) was commissioned in September 1954. She was “underway on nuclear power” in January 1955 and crossed the North Pole in 1958.
[/QUOTE]
there were 3 years between her operational date and the year she went to the NP. As for my definition of real missions, in the context of the cold war, would generally be something like this: a mission where a sub tails an enemy ship with the intent to kill them if the nuke war begins, or invading enemy waters to conduct covert spying operations, or infiltrating areas in int. waters cordoned off by the enemy to conduct weapons tests etc with the intent of obtaining operational information. Basically, any time they were ready to kill the enemy vessel or any time they were so close to enemy waters/operations that depending on the mood of the enemy they could be killed outright if detected.

That said, there are plenty of operations with inherent risks, such as the NP expidition by the Nautilus, that don’t involve death to or from the enemy but the elements alone. I don’t mean to take anything away fromthe guys who pulled off the very dangerous under ice etc. missions but remember rickover basically did the NP mission for PR for his pet project. The Nautilus simply wasn’t built to do under ice research or endurance or whatever missions, it was built to find, fix, and destroy the enemy’s of the US. So if it wasn’t a trigger pull away from doing so, its not a ‘real mission’ in my book, its training or research or what have you.

[QUOTE=robby]
Uh, no. :rolleyes: I don’t think you are grasping the mechanics of a 9,000 ton vessel..
[/QUOTE]
Well that’s why I asked, I knew it was improbable but I’m trying to think outside the box.
Just read about the Jimmy Carter ~pg 342 of BM’sB and how it was extended in length etc to accomodate the facilities necessary to continue the under water wire taping and enemy weapon’s salvage conducted by the Halibut, Seawolf (#2), and the Parche.

Well, I was on a LA class once 10 yrs ago, I know the prop is huge for the larger (like the new Seawolf) subs.

That would do the trick huh? same result with a less complicated system. hadn’t thought of that possibility.

16

[QUOTE=Chouinard Fan]
Are you kidding? If the Brad is expensive then you need to think about dropping the pay for your elected officials (or the A.F. or Navy budgets). I had 10 M2A2 Brad’s, 11 M113 APC’s, 20 HMMWV’s etc. (as many vehicles as a battalion normally) and it still only came to $50 mil and that’s including all of the weapons, wrenchs, computers, and repair parts etc. that go to make them all work, and maintain them.
Basically a little bit of money (for the fed) for a whole lot of combat power.

If you are remembering The Pentegon Wars with Dr. Frasier Crane then, yes, be a critic of the Brad, but from first hand knowledge it is just like the M-16. Sure it started off poorly, but boy doesn’t it kill efficiently now?

Should I even mention that we got our $3 billion out of the Ohio’s when the USSR collapsed and that reusing them now is actually a efficient cost savings?
[/QUOTE]

This reminds me of reagan’s invasion of the island of Grenada. We decided that every service branch had to be involved, so instead of just dropping the air cavalry in (and taking out the few, poorly-armed grenadian soldiers), we had to have a massive , complicated operation involving seal teams. the only problem was, a few seals got dropped off too far away, and drowned. it didn’t matter, the shooting was over by the time they got ashore. So thats what we’ll be doing with a huge and costly nuclear sub-risking the boat in shallow water to drop off a few commandos. Nice public relations, but a complete disaster-what if the sub goes aground? I can see it now-Islamic terrorists take over Mogadishu- Bubaya decides to send in the seals-captain of the sub miscalculates the tides, and $3 villion sub goes aground (we have to wait till civilian tug can steam up the coast from mombasa. imagine how that would look!

17

[QUOTE=ralph124c]
This reminds me of reagan’s invasion of the island of Grenada. We decided that every service branch had to be involved, so instead of just dropping the air cavalry in (and taking out the few, poorly-armed grenadian soldiers), we had to have a massive , complicated operation involving seal teams. the only problem was, a few seals got dropped off too far away, and drowned. it didn’t matter, the shooting was over by the time they got ashore. So thats what we’ll be doing with a huge and costly nuclear sub-risking the boat in shallow water to drop off a few commandos. Nice public relations, but a complete disaster-what if the sub goes aground? I can see it now-Islamic terrorists take over Mogadishu- Bubaya decides to send in the seals-captain of the sub miscalculates the tides, and $3 villion sub goes aground (we have to wait till civilian tug can steam up the coast from mombasa. imagine how that would look!
[/QUOTE]

Well, when you think about it, all the subs run tactically in shallow waters (the Bering Straight, and what seem to be shallows on the way to the ice North of Sweden etc) and its no big deal. Also, the sub doesn’t have to go in truly shallow waters where the tides would affect any chances of grounding, the SSBNs are ~300 ft. long, even if they were still under water you could see the very sub looking shape in water that shallow. The SEALs can launch from zodiacs etc underwater and then drive in. the sub simply doesn’t have to get that close to shore.

On a similar note though, there is a mission recounted in BM’sB where one of our attack subs went not just into Soviet waters, but INTO the USSR. The CPT took it right up one of the deep water river ports. the Ensign said he could see a dock ~30 ft away… Now the SSBNs are much bigger then most SSNs but still. If we can take one up a river I don’t think we need worry that a SSBN will run aground.

18

Try this missive:

OUCH, not only did you screw up so bad as to be relieved but to have it immortalized on the wiki… Double OUCH.