BMT SSGT (Ship Submersible Gas Turbine)

[Vepr157]

But even the Ohios or Seawolves could not run at full power on Natural Circulation. I believe that the new Columbia class and Ford class can run at full power on natural circulation, however. Took a while to work that out.

Just a note: the S6W is actually a forced-circulation plant. In the words of Admiral McKee, natural circulation was considered to be a bit "too ponderous" for the Seawolf's characteristics. Combining the low-flow design of the natural-circulation plants and advances in main coolant pump design, the S6W was apparently able to meet the Seawolf program noise goals without the need for natural circulation. I would assume the same is true of the S9G, A1B, and S1B.

 

[acelanceloet]

Another question for me be does the turbine need to be big enough to actaully DRIVE the sub.

As in have the... Full 7000 horsepower rating from 3 diesels going by the Collins.

or Can you use a smaller single turbine used to charge the Batteries?

Like there is serouis talk of making a pure battery power attack sub thanks to new batteries having enough power to make that feasible. Heck tge Japanese newest subs do away with their AIP systems to double up on batteries so the AIP unneed. So take that concept...

But can you use a smaller turbine to extend the range instead of a similar rated diesel to save weight or space? With that savings being used for more batteries or fuel.

The answer to this is yes and no.
Extending range of a battery by burning some fuel on the surface does help. There is a ton of energy in fuel, so a ton of fuel you bring with you does a lot more for your range then a ton of batteries.

However, most submarines want to spend as little as possible time on the surface. Which means, for such a use profile, a very big turbine and big generator would make more sense then a small one. Gas turbines are actually not bad in that respect, as you can get a lot of power into a low weight, small form factor (which is one of the reasons why they are so popular for warships) as long as you can get the exhaust out and the air in. However, generators and AC-DC converters that can put a lot of power into batteries tend to be not very small and light. So while the thought is not bad...... putting that power into your propeller shaft and keep the batteries or underwater-use propulsion entirely unused during the transit during which you have no issue with being spotted is a more sensible approach because of that.

 

[Scott Kenny]

Tangential, there was mention in earlier posts about USSR subs that could deploy 'scoops' to assist cooling: Is this related to the infamous 'Caterpillar' drive featured in eg 'Hunt For' ??

No, the scoops are there to use the ship's forward motion instead of a mechanical pump to push water through the steam condensers.

Just a note: the S6W is actually a forced-circulation plant. In the words of Admiral McKee, natural circulation was considered to be a bit "too ponderous" for the Seawolf's characteristics. Combining the low-flow design of the natural-circulation plants and advances in main coolant pump design, the S6W was apparently able to meet the Seawolf program noise goals without the need for natural circulation. I would assume the same is true of the S9G, A1B, and S1B.

I'd heard it was natural circulation at low power and forced circ at high power, similar to the Ohio plant, just able to use NC at higher power levels. Ohios can cruise along at patrol speeds with the reactor cooling pumps off, but still have Main Seawater pumps for the steam condensers.

 

[1635yankee]

Not a bad description, though it may actually date to WW2. Definitely dates to the Type XXI "e-boot" in post-war testing and Nautilus.



Yes, that's one of the advantages of turbo-electric drive like the French use. No reduction gears to make noise.

Then there's other bits and pieces you can do to further quiet nuke boats:

• But even the Ohios or Seawolves could not run at full power on Natural Circulation. I believe that the new Columbia class and Ford class can run at full power on natural circulation, however. Took a while to work that out.
• Then you add scoop injection main seawater, so you don't need pumps to cool the secondary. That's how the Narwhal SSN671 worked, but it required violating the rules on SubSafe valve sizes (scoops are a LOT bigger than what you need for pumps). IIRC the Soviet Typhoon class also uses scoops.
• I _think_ there's a way to get the secondary loop to run without needing pumps, but I'd need to sit down and sketch a lot to even come up with an idea.

Until you apply all that stuff, a good SSK or AIP boat is quieter.



I'm not entirely sure how well that'd work with getting enough heat out of the GT for the nuclear plant.

But if someone can find a copy of that article I'd love to hear more about the proposal!

Getting rid of heat? Sea water heat exchangers. One has to get rid of a lot of heat from a PWR, too. Probably less than 30% of the energy produced by a PWR gets turned into useful work

 

[Scott Kenny]

Getting rid of heat? Sea water heat exchangers. One has to get rid of a lot of heat from a PWR, too. Probably less than 30% of the energy produced by a PWR gets turned into useful work

No mention of a seawater heat exchanger in the articles for the closed-cycle gas turbine.

 

[Vepr157]

I'd heard it was natural circulation at low power and forced circ at high power, similar to the Ohio plant, just able to use NC at higher power levels. Ohios can cruise along at patrol speeds with the reactor cooling pumps off, but still have Main Seawater pumps for the steam condensers.

In the words of Admiral McKee (in his Naval Institute oral history):

"The success we enjoyed in development and design for the SSN21 propulsion plant was another high point. It was remarkable. We set a quieting goal that nobody thought we could make. We developed silent main coolant pumps. I felt that natural circulation plants were a little too ponderous for an SSN. We were able to improve on Trident quieting at all speeds with a reduced flow forced circulation plant.
...
One of our prime contractors developed those new main coolant pumps. I was there for the first run. I stood beside the pump, with my hand on it, and asked: “Okay, when are you going to start it?” They said, “It’s running.” I couldn’t tell whether it was stopped or started. That remarkable technology should also be in Virginia – the SSN that will follow the Seawolf class.
...
We developed techniques to apply high power-to-flow design principles developed for use with natural circulation plants to low flow forced circulation plants. That has enabled much higher reactor power with much lower pumping power, giving us the flexibility of forced circulation without the operational complexity."

 

[publiusr]

Problem is, you can't drive very fast at periscope depth without showing a lot of wake, and you will run into control issues keeping depth.

You're NOT going to do 20 knots broached like that. You'll be lucky to do 14, and even going that fast will beat the crap out of the screw from cavitation and let everyone in the world know where you are via radar and wake.

In other words--a glorified cocaine sub.

 

[TomS]

In other words--a glorified cocaine sub.

The designers understood the problems here. For SSGT, the high-speed mode was not something they proposed for operations in theater where someone might be hunting the sub, it was for high-speed transits outside the threat area. The targeted users were navies like the RAN, which are based significant distances from their principal operating areas and were thought to face little threat in transit.

 

[Firefinder]

So like the old WW2. Fleet subs which travel most of the way to their patrol AOs on the surface doing 15 knots unless they hit a storm or something.

 

[Scott Kenny]

The designers understood the problems here. For SSGT, the high-speed mode was not something they proposed for operations in theater where someone might be hunting the sub, it was for high-speed transits outside the threat area. The targeted users were navies like the RAN, which are based significant distances from their principal operating areas and were thought to face little threat in transit.

Beating the crap out of the screw from cavitation is still not good, because that raises your on-patrol noise levels as well.

Assuming it doesn't just break the screw entirely.

 

[publiusr]

I wonder if anyone thought of kite sails on subs. Sail far above the water, the submarine beneath the waves—-only lines passing through the surf.

 

[GTX]

I wonder if anyone thought of kite sails on subs. Sail far above the water, the submarine beneath the waves—-only lines passing through the surf.

Kind of defeats the stealthiness of a submarine.

 

[Grey Havoc]

Kind of defeats the stealthiness of a submarine.

Depends. There were some interesting experiments by a few navies during the last decade or so on the use of kites as not only as a fuel saving/quieting measure, but also as a EW and/or Comms antenna. That does suggest some possibilities.

Separately, it would be possible to build a kite sail out of RAM materials and using shaping techniques to reduce the likelyhood of detection by enemy radar systems, shore (including OTH), ship, or even satellite based. It would be fairly expensive though.

 

[GTX]

Depends. There were some interesting experiments by a few navies during the last decade or so on the use of kites as not only as a fuel saving/quieting measure, but also as a EW and/or Comms antenna. That does suggest some possibilities.

That was for surface ships, not submarines

 

[Foo Fighter]

For the patrol area and distances involved, I am leaning towards nuclear being the only realistic option.