From: "Sean J. Roc D'Arcy" <bphdarcy@ubvmsb.cc.buffalo.edu>
Subject: Re: Discussion Of Shallow Water ASW
Organization: University at Buffalo
Date: Tue, 17 Nov 1992 17:40:26 GMT


From "Sean J. Roc D'Arcy" <bphdarcy@ubvmsb.cc.buffalo.edu>

In article <Bxo178.63D@law7.DaytonOH.NCR.COM>, JMARTTILA@finabo.abo.fi (Fast-Eddie Felson) writes...
> 
>From Fast-Eddie Felson <JMARTTILA@finabo.abo.fi>

>Using long array devices for passive sub detection is possible and even
>effective. The convergence zones are just one little detail. Towed array
>sonar allows you to listen to the noises the sub makes instead of you own
>engines and also peek under the thermal layers (there are such things in
>shallow water too O:).


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.  

On the subject of towed array:  One of the main purposes of a towed array 
isn't so much to not hear your own engine noise, a towed array will detect 
the noise from its host boat very well.  One nice function for surface 
vessels is the ability to listen at great depths (you already mentioned).  
Another function is to address the problem of baffles that moving vessles 
create.  I would say the primary function is that it  gives any vessel many 
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. 

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.
> 
>>In shallow water other ASW devices besides sonar excell.  IR and actual
>>visual spotting come to mind.  MAD should still retain most if not all of
>>its effectiveness.  Also, I would think surface wakes produced by the
>>submerged boat would be much more prominant.
> 
>In peacetime situations passive acoustic detection is the most important,
>because MAD, IR and other clerical methods have a very limited range and
>thus are not suitable for controlling large areas. Passive acoustic
>methods also require much less resourses. The other methods (mainly active
>sonar) are more suitable for exact target positioning and fire-control.
> 
>>I think one of the major problems in shallow water ASW is the performance
>>of ASW torpedoes.    How well would a Mk-46 fare in a shallow water
>>situation?  In many shallow water situations depth charges might be more
>>effective.
> 
>It depends on the situation. If the sub is hiding close to seabottom and
>the bottom is rough causing a lot of false echoes a depth charge would be
>the right choise. However, if the sub is moving it's a decent target for
>a torpedo almost like in any other environment. As much as I know the
>Swedes have recently aquired new torpedoes to be used in shallow water so
>at least they believe it works O:)
>

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 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.

>First I have to point out that no DE submarine is made to pursue its target,
>but to wait stationary and silent on the seabottom. DE submarines fit well
>in this kind of tactics - after turning off the engines they are practically
>invisible for passive sonar and due to their small size they are also a very
>small active sonar or MAD target.

A good point here also.  A lot would depend on the ordinance carried by the 
submarine.  A long range torp allows for mimimum manuevering on the part of 
the submarine.  Converely, a short range ordinance will require some if not 
a good bit of movement on the part of the submarine.  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.

>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.

SJRD


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