Page 2 of the H4.1 Data Annex is titled A Guide to Trilogy Ship Listings. "ESM/AIR: Surface ships use only the first field while subs use the second. No surface ships carry an ancoustic interecept receiver. The generations are listed as 1st/2nd/3rd Gen. For subs, the two ratings are separated by a slash."

 

In working up an Improved Los Angeles Class SSN, its ESM/AIR rating is 3rd/4th Gen. How are the 3rd and 4th Gen ratings utilized? I'm assuming 3rd Gen ESM would be while on the surface - a la a surface ship? I'm drawing a blank on the "AIR" rating.

 

Thanks

Thanks to Dave Schueler's response:

 

"...A submarine would have to raise it's ESM mast to use ESM (although most periscopes also have an ESM receiver mounted on them). So basically to use ESM the sub would have to be at Periscope/Snokeling depth or on the surface with a mast up.

 

The AIR is basically a passive sonar that detects active sonar, but has a fixed maximum range based on the frequency of the active sonar (although the detection is halved if it goes across the thermal layer). It is usable at any time, unless the sub is in drydock 8^). There is a table in the rules that has the statistics for AIRs..."

Thank you for the AIR (Acoustic Intercept Receiver?) explanation Pete.

Thank you for the AIR (Acoustic Intercept Receiver?) explanation Pete.

hehe, as I responded to Dave, I cannot fathom how I could never relate the "AIR" rating to the relevant Acoustic Intercept Receiver rules. As soon as he pointed it out, like in so many of my other harpoon experiences, the light bulb just started glowing like nothing else!

Don't feel bad, I couldn't even figure out that your initial post on this thread was actually a question.

Don't feel bad, I couldn't even figure out that your initial post on this thread was actually a question.

How are the 3rd and 4th Gen ratings utilized? I'm assuming 3rd Gen ESM would be while on the surface - a la a surface ship? I'm drawing a blank on the "AIR" rating.

 

I was under the impression that the internet alleviated the need for most puntuation, including question marks. (the preceding is a gratuitous period)

And for those of you brave enough , , the next topic to tackle is Convergence Zones

In that case ...

 

From Scott Gainer's "A Guide to Naval Tactics":

 

"Convergence zones (CZ) are another aspect of the bending of sound in water and are chiefly based on the changes in sound speed with increases in depth. Sound typically undergoes a significant decrease in sound velocity when it first enters the water then increases in velocity with increasing depth due to changes in density related to compressibility. Once the speed has increased to match the velocity at the source, called critical depth, the sound travels pretty much horizontally. Past critical depth into the realm where the original velocity has been exceeded the sound bends upward creating parabollically arcing paths through the water. When it strikes the surface, in an area called the annulus, it is reflected downwards again and repeats the process until attenuated or obstructed. Unlike the more usual portrayal in games CZ don’t form concentric cylinders of ensonified water but rather a series or curved three dimensional volumes so that a submarine that is at CZ range could potentially be below the CZ path and thus remain unseen. This also applies to areas between the annuli where shadows will develop.

 

CZ require a minimum depth of 400m to form, at which depth they have about a 50% chance of developing, and increase in probability with depth. 600m yields an 80% probability of CZ production with near certainty of CZ in deeper waters.

 

Topographic features including seamounts, islands and mid-oceanic ridges disrupt CZ paths as do currents with significant changes in water temperature, such as the Gulf Stream.

 

Convergence zones (in this case we are using the terms convergence zone and annulus interchangeably) typically develop at thirty mile intervals with the width of the annulus increasing with distance. The first CZ at 30nm typically has a surface annulus 3-5 nm wide, the second, at 60nm, 6nm wide, and the third, at 90nm, has a width of 9nm. Fourth and Fifth CZ are possible but not common. CZ ranges in the Mediterranean are reduced due to layers of warm water near the bottom.

 

Contrary to what players of computer Harpoon (prior to H4, anyway) have experienced, active sonars, as well as passive sonars, may make use of CZ. This is especially true of the high powered, low frequency, sonars found on such platforms as the Spruance and Udaloy class destroyers. Keep in mind though, that an outbound sound pulse in a CZ may be heard much farther away than the reflected energy will be detected by the emitting platform, the opposition may spot you before you detect him.

 

This last tendency of active emitters to be detectable beyond their detection range is a function of the inverse square law where energy decreases as a function of the inverse of the square of the distance (E=1/D2). If you have a calculator handy try replacing D with 1, 2 and 3 and see what the energy at each distance is then consider that the sensor has to detect sound that has gone out and then come back resulting in an E of something like 1/36. This is basically the principle that car radar detectors and passive EW (see below) rely upon."