Military History | How To Make War | Wars Around the World Rules of Use How to Behave on an Internet Forum
Submarines Discussion Board
   Return to Topic Page
Subject: Umbilical Submarine Tow.
HeavyD    4/18/2012 7:18:26 PM
One of the drawbacks of the USN considering SSKs is the limited range/speed while submerged. Limits it's ability to sprint to trouble spots undetected. So...how about an umbilical tow? In blue water a SSK hooks up to a 300 foot (or whatever length is determined optimal) power/comm umbilical and the SSN (Ohio or perhaps even a Virginia). A full 25 - 30 knots may not be achievable, I'm no electrical engineer, but certainly 15 - 20 knots. The concept is not much different that a towed array, the comm link includes mutual real-time depth readings so the slaved sub can maintain a safe depth differential. The development costs would be fairly minimal - hell we could lease a SSK for proof of concept and trials. Of course the Navy really doesn't want SSKs, even though there is only 5+22=27 crew on a Type 212 and 15+120=135 on a Virginia. I don't believe there is a technical challenge here that is unworkable, just an attitudinal one. Why would we want to? Well certainly there are missions where a sub like a Type 212 is better suited than a 16000 ton ex-boomer. I've read that the Germans are experimenting with a periscope-deployed 30mm, and full-size sub could better support a covert mission with tube-launched AA missiles and Harpoons, and potentially even with a pod of 160mm rockets. Or a FireScout. Minelaying is another mission that the smaller sub could fulfill better than a SSN in some circumstances. I wonder how the speed and signature could be affected? Continuing to think outside the box, perhaps the smaller sub could be slaved to the power supply of the Ohio/Virginia to power it's electric motors as well. If not to power the motors the mother-sub could certainly power life support, allowing the smaller sub to be fully or partially manned in case emergency un-coupling is required.
 
Quote    Reply

Show Only Poster Name and Title     Newest to Oldest
Pages: 1 2
WarNerd       4/20/2012 6:02:00 AM
One of the drawbacks of the USN considering SSKs is the limited range/speed while submerged. Limits it's ability to sprint to trouble spots undetected. So...how about an umbilical tow? In blue water a SSK hooks up to a 300 foot (or whatever length is determined optimal) power/comm umbilical and the SSN (Ohio or perhaps even a Virginia). A full 25 - 30 knots may not be achievable, I'm no electrical engineer, but certainly 15 - 20 knots. The concept is not much different that a towed array, the comm link includes mutual real-time depth readings so the slaved sub can maintain a safe depth differential.
Could you be a little clearer on this concept? Are you only transmitting power through the cable and using the SSKs engines for propulsion? Or is this an actual tow cable?
 
Either way, electrical or mechanical, that umbilical has to transmit all the power needed to drive that SSK at whatever speed you choose. And then there is the mechanical drag on the umbilical itself.
 
Total tension for a simple tow will probably be on the order of 700 tons for straight pull on a Type 212 at 20 knots, probably double that since you are maintaining a depth offset. The tow cable should also be neutrally buoyant to facilitate making the connection up, particularly underwater. The tow cable is going to have to be large, probably 4” to 8” in diameter.
 
Supplying power to the SSK through the umbilical is possible, but extremely dangerous. The problem is the end connections are under continuously varying loads and must remain water tight while able to make and break repeatedly. You will need a capacity of about 2 MW for a type 212 at 20 knots.
The development costs would be fairly minimal - hell we could lease a SSK for proof of concept and trials. Of course the Navy really doesn't want SSKs, even though there is only 5+22=27 crew on a Type 212 and 15+120=135 on a Virginia. I don't believe there is a technical challenge here that is unworkable, just an attitudinal one.
Not a chance this will be cheap or simple. As for technical challenges, you are going to have to redesign the SSN to carry, deploy, and retrieve the tow umbilical/cable. It is going to be an entirely new class of submarine.
Why would we want to? Well certainly there are missions where a sub like a Type 212 is better suited than a 16000 ton ex-boomer. I've read that the Germans are experimenting with a periscope-deployed 30mm, and full-size sub could better support a covert mission with tube-launched AA missiles and Harpoons, and potentially even with a pod of 160mm rockets. Or a FireScout.
Deploying aircraftfrom a submarine? Time to get your meds checked!
Minelaying is another mission that the smaller sub could fulfill better than a SSN in some circumstances. I wonder how the speed and signature could be affected? Continuing to think outside the box, perhaps the smaller sub could be slaved to the power supply of the Ohio/Virginia to power it's electric motors as well. If not to power the motors the mother-sub could certainly power life support, allowing the smaller sub to be fully or partially manned in case emergency un-coupling is required.
For minelaying you could just use MK 67 Submarine Launched Mobil.... No need for an SSK.
 
Quote    Reply

HeavyD       4/20/2012 12:44:18 PM
I was thinking just power, not tension, to enable the SSK to provide all of it's own propulsion.
 
1.  An Ohio's electric motors are 45mw capacity, a Type 212 is 1.7 MW, or less than 5% of the Ohio's capacity.  The Ohio can achieve 25 knots submerged, to throttle back to 20 knots will reduce power consumption by well over 20% (9 megawatts), clearly more than the SSK could ever use.  Clearly a Virginia is also capable of generating more than 2MW of excess juice @ 20 knots.
 
 
2.  The subs would not be maneuvering together, just making passage at depth.  Slight tension could be maintained to allow a nose-to-tail orientation (minimizing drag) which would also communicate/moderate the safe distance (i.e. tension lessening indicates that slave should power-down a bit, increased tension the opposite.)
 
3.  We have subs with towed array pods already - no need for a complete re-design.
 
4.  Even if the practical sustained speed is 17.5 knots this is 480 miles a day.
 
5.  We could do a similar arrangement with a surface ship providing the power (think container ship with the sub 150 feet (from sail ) below.  What a great way to get a small sub up close and personal to a port. 
 
Why?  Well let me ask this:  How would the US know if there were a Kilo lurking 100 miles offshore from New York?  probably because a satellite would pick it up when it snorkeled trying to get there, and it couldn't linger for long once it was there.  It has to come up.
 
 
Quote    Reply

JFKY       4/20/2012 2:00:30 PM
1) So under your plan we have to have TWO Submarines, to deploy 1?  And this makes any kind of sense how? You've deployed an SSN AND an SSK.  You haven't saved a dime...you have the cost of the USS Virginia AND the Type 212.
 
2) You'd have to rework both the SSN and the SSK that's not cheap.  And the SSN doesn't run off of ELCTRICITY, but steam.  The power plant makes steam, which is converted to kinetic energy in a turbine.  What does the SSN provide, thru the tow, to the SSK?  It doesn't provide steam, that doesn't power an SSK.  It doesn't provide electricity, unless you have the SSN reworked to provide enough power to propel both itself, and then enough electricity to propel the SSK-and that assumes the SSK is diesel-electric.
 
Again, why is it advantageous to deploy 2 submarines when you can just as easily deploy the one, nuclear submarine?
 
Quote    Reply

HeavyD       4/20/2012 4:09:01 PM
Steam...nevermind!
 
And you had it backwards, it wouldn't take 2 to deploy 1, it would take 1.25 to deploy 2  (type 212 = 25% of cost of a Virginia).
 
 
 
Quote    Reply

JFKY    Again   4/20/2012 4:24:56 PM

1 Type 212 is NOT steam powered...hence the umbilical from an Ohio or Virginia is not useful.

2. No it takes 2 SS to deploy one SSK...ONE SSN to tow and the SSK to be towed, hence 2 submarines, for each deployment and 162 sailors rather than 27 or 135.

3. It makes no sense.

 
Quote    Reply

Reactive       4/20/2012 7:21:34 PM
I like this idea.
 
The problem being that before distributing electricity was feasible an IEPS design would be required, in all likelihood it will be on the next-generation of subs anyway.
 
 For this application I think it's quite fair to say that the problem solved is relatively minimal considering the investment required, it would make more sense to routinely forward deploy SSK's (or stick to SSN's ; )
 
However, the concept of allowing an SSN, or any reactor equipped vessel with up to tens of MW of reserve capacity to power other systems onboard or offboard is valid imv. I don't think OP's scenario is not necessarily the most likely but neither does it deserve sneers, the concept of future SSN as mobile, stealthy power generator is quite valid.
 
"An integrated electric power system will allow tomorrow's submarines to make greater use of rechargeable off-hull vehicles, payloads, and sensors to extend the submarines' tactical reach and safeguard operations in high risk and restricted areas." 
 
navy.mil/navydata/cno/n87/usw/...  
 
 
 
Quote    Reply

LB       4/20/2012 8:38:29 PM
The main point that the USN requires SSK's has not been established.  Assuming the requirement existed then how they are to strategically deploy is another matter.  While one could make a reasonable argument for USN SSK's it's simply politically a non starter.  The USN doesn't want Congress thinking at some point it can reduce SSN's in favor of SSK's.  
 
Moreover, for the USN SSK's probably only make sense for shallow water operations and training.  We have lots of allies with SSK's that assist with both.   Moreover, SSN's can and have operated in shallow water.  What is going to happen in future is SSN's operating higher capability UUV's to extend the reach of the sub.
 
So the real question is exactly what mission(s) exists that would be better performed by an SSK rather than a USN SSN or any other platform?  It's also worth noting that small European SSK's are not suitable for Pacific operations.  Australia and Japan both operate SSK's twice as large with larger crew.  The follow on to Collins is projected to cost between $1.4 and $3 billion so it's possible it will cost roughly the same as a Virginia SSN.  
 
 
 
Quote    Reply

HeavyD       4/20/2012 10:41:54 PM
My initial thought was to piggy-back a SSK on an Ohio, but then the thought of slaving to power to assist with propulsion got me to thinking about the umbilical concept, but that is a non-starter as SSNs are steam-powered as was pointed out.
 
LB is spot-on that in that many of the procurement issues are political and not practical in nature.
 
Re:  the need, again as my initial thought was to piggy-back a SSK on a tomahawked-Ohio in order to have littoral abilities for missions such as mining, dropping off and retrieving special forces, underwater covert ops/intel, and whatever else a 1500 ton sub can do better than one 10 the size!
 
It would also answer the objection that SSKs can't make it to trouble spots as rapidly as SSNs.
 
And yes, we would then get a two-fer on deployments if the SSK goes wherever an TommOhio goes.  Like off the coast of North Korea or in the Persian Gulf right about now...
 
 
 
Quote    Reply

WarNerd       4/23/2012 2:46:48 AM
I was thinking just power, not tension, to enable the SSK to provide all of it's own propulsion.
 
1. An Ohio's electric motors are 45mw capacity, a Type 212 is 1.7 MW, or less than 5% of the Ohio's capacity. The Ohio can achieve 25 knots submerged, to throttle back to 20 knots will reduce power consumption by well over 20% (9 megawatts), clearly more than the SSK could ever use. Clearly a Virginia is also capable of generating more than 2MW of excess juice @ 20 knots.
The problem is not the power (others have covered the steam/electric issue), it is the umbilical.
2. The subs would not be maneuvering together, just making passage at depth. Slight tension could be maintained to allow a nose-to-tail orientation (minimizing drag) which would also communicate/moderate the safe distance (i.e. tension lessening indicates that slave should power-down a bit, increased tension the opposite.)
What makes you think that the umbilical will be ‘springy’?
 
Your first indication that the trailer is out of position will be the umbilical tearing out of the socket, followed by a pair of explosions, the first will be a steam explosion when 2MW of power is dumped into conductive salt water, followed a fraction of a second later by the windings on the now short circuited generator being vaporized. OK, it is not quite that bad if the safeties work, but the connectors and umbilical are going to be in the shop for a while for repair and testing, and probably both subs go into drydock. This is NOT something you can repair in the field.
3. We have subs with towed array pods already - no need for a complete re-design.
Glad to hear it.  Now a couple questions:
1. How many megawatts do those tow array pods use? Probably about 0.00001 MW I suspect. Think maybe you might need a slightly larger conductor for 2MW?
 
2. How big is the umbilical? For the towed array probably a ½” to ¾” steel rope with a small coax cable spiraling around it and a thin plastic sheathing. For a 2MW umbilical – well for a back of the envelope calculation let’s assume a 2000 volt system, so 1000 amps, 3 phase. The umbilical will probably need 6 x 1.5” copper conductors (6 is a magic number for a subsea umbilical because it produces a round symmetrical bundle. That is critically important for an application such as this.), plus insulation, outer sheathing, and syntactic foam to produce a neutral buoyancy. For a guess lets use 10” in diameter.
 
3. What is the mass of the pod and wire? Probably less than a ton. The 2MW umbilical will probably weight in at 100+kg/m.
 
4. How big is the capstan and take-up reel? Probably 1m or less for the towed array. For the 2MW umbilical it will have to be at least an order of magnitude larger. Probably have to use a rack on the hull inside one of the center ballast tanks and a bobbin to wind the umbilical in it like a spinning reel. Track style tensioners, a minimum of 2 for safety, inside the aft ballast tanks.
 
5. The connectors. Let me be blunt, subsea power connectors are NOT DESIGNED FOR MECHANICAL LOADS. Anything that causes the connector to flex is likely to create a gap in the insulation and allow conductive salt water in is an instant disaster. These will even have to be able to rotate, which has not been done before.
A power umbilical is nothing like a towed array. Designing this will not be trivial, it is a {expletive} nightmare.
 
Look, if you are going to use another vessel for clandestine deployment of an SSK just modify a large ship into a mother ship with the classic large underwater hatch to winch the sub up inside through and then close. Be sure to include quarters on board the mother ship for the sub’s crew so you don’t have a mutiny. It will be a hell of a lot simpler and cheaper.
 
Quote    Reply

Reactive       4/23/2012 12:27:35 PM
I don't think anyone said it was trivial, and I think it's clear from the first post that it's more than a little impractical, more interesting is the related capability of using significant power supply from a future Sub IEPS most obviously for charging submerged arrays and UUV's but given the abundance of highly-mobile nuclear power it's not hard to imagine exotic uses, powering weapon systems, creating propellant, powering sensor arrays.. the growing modularity of naval systems means that there will likely be future requirements even if they sound currently sound outlandish.
 
Very few applications, would require anything close to 1MW- even if they did it would be far more efficient to install the appropriate transformers and go up to 6-7KV - a 2MW power supply @6+KV is regularly transferred via a single cable for the offshore wind/renewables industry. Yes that does present its own challenges, especially in this context, and no I don't much like the idea but I'm sure appropriate safeguards and circuit-breakers could be put in place if anyone actually had a good reason to supply so much power.
 
 
 
 
Quote    Reply
1 2



 Latest
 News
 
 Most
 Read
 
 Most
 Commented
 Hot
 Topics