From: JMARTTILA@finabo.abo.fi
Subject: Re: Discussion Of Shallow Water ASW
Organization: Turku School of Economics
Date: Thu, 19 Nov 1992 14:02:44 GMT


From JMARTTILA@finabo.abo.fi

>From "Sean J. Roc D'Arcy" <bphdarcy@ubvmsb.cc.buffalo.edu> 
> Unless the array has some type of boyance device (which I believe some do) 
> it can't be used in shallow water at any great length.  After doing some 
> calculations it would seem that in water less the 200 ft. deep, there would 
> be no convergence zone at all.
> more hydrophones in many more places.  A good towed array will allow  
> triangulation for distance, a single bow sonar dome would have quite a 
> problem with out moving to  a new location.  I think this is one big 
> function of a towed array many people keep overlooking.  Passive sonar is 
> not real efficient in giving range when the sensors are very close 
> together. 
  
These devices, at least some of them have some sort of a steering system
which allows floating them in different depths. Therefore shallow water is like 
any other environment. The length doesn't need to be 2 miles to make it
effective. Actually 500 yards would do fine in shallow water - you see, like
you mentioned there are no convergence zones in shallow water so the distances
are much shorter. Two measurement points 500 yards away of eachother give a
rather good fix on the target say, 10 miles away.
 
> About layers:  I guess a bit would depend on local thermoclime (sp?) 
> conditions and more on how on defines shallow water.  Coastal currents in 
> most cases eliminate any seperation of water into temperature gradiants via 
> the under-over surrents meeting  a land mass.

You are right... this depends a lot of the local conditions. For example in the
Baltic there are not too many of such currents. Therefore for example the
change of season causes quite stabile thermal differences. 
These currents might also actually create separations. When a warm current
meets a cold one the cold water tends to go down while the warm water stays
near the surface. This might happen for example near a river delta. 
 
> A point of clarification:  A few people who mailed me thought I was asking 
> a question about the Mk-46's performance.  I was using it as an example of 
> a troubled device in shallow water situations.  

I admit that you probably have to drop it relatively close to the target to
make it function O:)
 
> I have as yet not heard of this new shallow water torpedo the Swedes have.  
> Could you post or send me some information on it?  Also, who and what 
> country manufactures it?  Thanks.

I have unfortunately no further information about this except that it is of
French origin, if I remember right. I'm sure, however, that the Swedish readers
of this group can enlighten us about the case.
 
> On the subject of Iran and the Kilo, I'm not sure that Iran will have 
> access to something akin to the FUSSR MK-65.

If I remember right, the Kilo has only 533mm tubes so it can't launch type 65
torpedos. A couple of Kilos could, however block strategic routes like the
strait of Ormuz. This could be regarded as a serious threat since the ASW
forces of the local countries are not like the US's.

> >Nuclear submarines can't just like that turn off their reactor since it
> >takes time to turn it on. They are also much larger and hard to manoevre in
> >tight spaces. 
> But, they can turn them back quite a bit.  I believe at low output an US 
> LA class can turn off its circulation pumps and becomes very quite.  And in 
> shallow water, I don't know if the sound difference would be all that much.
> A lot comes down to the noise of the reactor/turbines/generator systems of 
> the sub.  While finding an November sitting on the bottom would be easy, I 
> don't know if one could even hear a Trafalgar.

Sitting on the bottom often means doing that for a relatively long time, not
just a few minutes. If the reactor is turned even to the minimum output, I 
believe the coolant devices are needed in the long term to prevent the reactor 
from overheating (I don't know the structure of the reactors they use in 
submarines, so I won't bet my head for it O:). 
I've heard that at least the Russian Victor III had a special battery powered
creep drive to avoid the reactor noise in slow speed combat situations. 

        JM

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    Jouni Marttila - Yo-kyl{ 11 B 25, 20540 Turku, FINLAND - +358 21 374624
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