Why The slow subs ?

Imbalanced,

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I was just curious as too why there are no super fast subs or attack type subs that
go really fast ? I mean in the air we have bombers (subs) but know attack subs (like a yf-22 equivalant).
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Actually, this is a very valid question. First, the Seawolf and some of the later Russian Nuke boats _can_ in fact 'supercruise' at around 20 knots, within a minimum noise threshold. This is quite a useful ability because with the proliferation of quieting technology, the ability to leave the enemies computed shot bubble is increasingly important.

Something that was known as far back as the Nautilus which was known to be able to leave behind (period '50s) USN ASW plots with ease.

It should however be noted that with the emphasis these days on inshore ops and supporting fires (CM) and even SOF actions, what you do once you are there is apt to be far less ASW oriented than simply station keeping with quick dashes inshore to drop off and retrieve small unit forces.

In this, maximum cruise speed is really only useful for rapid staging into and out of the patrol area because the nuke boats are already so big and so noisy that it takes awhile for them to get 'comfortable' in close, simply because they are so large and make such a 'hole in the water' effect which is not really maskable due to absent thermal layers and the effectiveness of modern actives and even laid-cable sensors.

If we faced an active submarine threat it would be tantamount to suicide to take them there.

Speaking of which, while others have mentioned flow noise and propulsor problems I would also like to add that, especially for attack boats, any attempt to go fast means running the pumps on the PWR or _Pressurized_ Water Reactor. Plant noise is the number one key signature on all boats, beating even blade counts in most conditions.

As far as going really fast, the key is not to not try and throw a brick through the water, sideways. Because a small robotic 'torpedo' like device can withstand both vastly greater pressure depths and have a HUGE advantage in surface drag over it's equivalent wetted area. Indeed, the British Spearfish was supposedly doing 65+ knots as long ago as the late 80's. With this kind of system, and especially multiple pairs of them in the water, you can avoid Sprint-Drift tactics (lunge and listen) and simply use the UUV's to go-Yankee intermittently as they come off high speed runs. Scare away wales, map seamounts, frighten off the steel sharks, whatever. Given that sound moves through water at around 2,500mph and the mini subs offer the relatively easy ability to porpoise over and under thermal layers as deep as 1,500-2,000ft, _so long as they are cheap_, they can beat any passive quieting system a sub can employ at tactical distances.

Indeed, since sound knows neither enemy or friend, it becomes possible for them to 'escort' slower manned boats with the latter serving as netcentric weapons cabinets to fire actual weapons onto bearing, leaving the scouts to function without worry over subsequent engagement tactics or threat to selves.

The only real problem here being that the best way to kill a sub is to loft a rocket boosted torpedo to it rather than drive one out at even SCT speeds. And we have lost Subroc and ASW-SOW as the principle methods of doing this.

Yet, given the increasing use of anti-torpedo weapons and the certainty that you can afford to lose a 10 million dollar AIP 'drone' sub far more often than a 2 billion dollar attack boat, the reality is that high speed operations are probably a lot closer than most people think.

If what I've heard about 'turning the water transparent' within 400ft of the surface with systems like April Showers and other methods are true, the real question is apt to be how long we maintain a large submarine force as potential (high tech) enemies become more overhead + SOSUS adept at creating bastion exclusion zones around their littorals.

Subs are incredibly vulnerable, exceptionally inefficient (per volume ton), _very_ hard to upgrade, assets. You take a hit and you're either dead immediately or a noisy cripple waiting for the coup. You lose a boat and not only have you thrown away the equivalent of a B-2 in unit costs but also have created a political disaster in the form of a 100-200 sailor mazcaz. If subs themselves have a use in future, it will therefore be (IMO) as spider-in-her-web platforms which exist solely to deploy sensor webs and possibly UAV to allow at least offboard tracking from range and possibly moored kill system intercepts as well.

With everything swimming in from a deployment area far out to sea, you remove much of the need to drive a boat tactically against any threat, including mines and inshore ASW aircraft which are again, quite lethal to big nukers.


KPl.

current subs are as fast as they are required to be! It will be a long time before we ever see subs that are substantailly faster than current models. To clear up some ealier points modern subs (in the west) use pump jets and not propellers as they are quieter and very efficient at slow speeds ( where a sub spends most of its mission at ~5 knots). Electromagnetohydrodynamics will never be used on a sub until there is a massive increase in the magnetic flux density available. Even with superconducting magnets the efficency of these systems is extramly poor. This is due to the conducting capability of saltwater being low. To get any effiency into the system you need much higher voltages and MFD than is available with current technology.

Current thinking for increasing the speeds of subs revolves around reducing the drag, this starts with making the most streamlined shape possible (we just about have that now) and then looking at further ways to reduce drag, such as super cavitation, shark and dolphin skin coatings, micro-bubble and polymer injection, boundary layer control and many many others.

For uptodate information on this, try getting hold of the conference preccedings of the 2nd ISSDR from last year.

aserc.pusan.ac.kr...


p.s. if you look closely at the pictures on that website i am hidden at the back somewhere!

There's another point. The more sound you make the less effective your sonar becomes since for Uboats its passive detection all the way! Passive detection is dependant on the ratio of the sound signature and the back ground sound..."signal to noise ratio".

As a rule detection ranges are in 10s of km and a fraction of that if the sub is super quite and really slow. Long range detection is possible through two techniques that I'm aware off, sound channels and convergence zones.

Sound channels are pecular alligments of water depth density temperature and selinity that conduct sound much faster than across the ocean. Some times detection ranges are possible in the thousands of km vs really noisy subs. But there is very little utility for that ultra long range detection since locating the target and attacking at that distance is out of the question.

Convergence zones [CZ] happen as soundwaves bend in the sea and eventually after radiating down to deep ocean they turn around and bounce of the surface , reflect and bounce again back down to the depths to the next CZ.

Most passive sonars that have CZ capability can pick out a target at 1-2 CZ away , while the more advanced maybe be able to detect at 3-4 CZ away. Each CZ itself is narrow about 10km so if target is detected fast action is needed to attack....thats one of the ideas behind SUBROC and ASW helos since surface ships can get CZ passive sonars from towed arrays. These CZ can be 20-30miles apart so at the very least they establish concentric trip wire zones that alert CZ sonar of a sub contact....especially important if your a frigate escorting a convoy or battlegroup. So a CZ sonar with 30 miles between CZ and up to 4 CZ can theortically detect a sub at up to 120-150 miles?

[edit on 22-6-2006 by psteel]

[edit on 22-6-2006 by psteel]