Convergence Zones

[Halcyon]

From the manual:

CONVERGENCE ZONE

As mentioned above, sound is bent back upwards by water pressure such that if the water is deep enough (~10,000 ft in the Norwegian Sea) it will ultimately return to the surface. The zone in which these sound waves return to the surface is called a Convergence Zone and can be 40,000-50,000 yards away. A ship listening with sonar in this zone could detect the emitter, even though the range is far beyond the distance the sound could travel along the surface.

I've also been reading the RSR novel, and at some point the Chicago's XO is talking to the skipper about how a contact may be 2 or 3 "convergence zones" away from their boat.

How exactly would they determine that?

Is there any way in cold waters to tell if you're detecting something from a convergence zone and what the range might be? Is it possible to get 2 or more CZs like it's written in RSR?

[Wiz33]

25000 yard is well within direct path range, CZ is usually just for detection. Most engagement will happen within direct path.

[-Pv-]

I would have to defer to KillerFish to see if they want to explain their reflection calculations, but the easiest answer up front is there is nothing in the Manual I have read, nor any specific display in the game which details this feature. At this point, I don't see any ADVANTAGE to knowing this detail in the game since it has no impact on your decisions and in the case of the book, made some interesting page filler.

As a theoretical model, this attribute is more important at extremely long range of 30 or more miles. The typical long range of engagements in CW is 12 miles or less in which the number of convergence zones involved is a non-factor.

ADDED:
Thanks Wiz33. I'll add that the original RSR game did not provide this information either that I recall.

-Pv-

[Halcyon]

So why is it in the manual? Just a page filler?
Makes me wonder what else doesn't matter...like bottom bounce.

They explain that concept but often times you have no idea what shape the bottom is or what it's made out of (sand vs rock vs whatever). The manual could be a bit clearer.

[Killerfish Games]

Convergence zones do matter, mostly for contacts that you've lost.

They occur at longer distances of 35-44km. So if you lose contact via the direct path, when the vessel crosses the convergence zone there is a chance that you'll pick it up again.

At combat start, convergence zones are less important as the game brings you in closer for combat.

[-Pv-]

Thanks for the response KF. At those long distances, I pop up the radar for a snapshot since the threat of an answering shot seems fairly low, then deep dive to close.

I'm corrected in that the Manual does mention this on pg 29. When I mentioned page filler, I was commenting on the book not the game.

Added:
This still leaves the original question if it's important to KF to provide the zone count (if there is one) to the user in the interface.
-Pv-

[LTJGBeam]

Originally Posted by Killerfish Games

Convergence zones do matter, mostly for contacts that you've lost.

They occur at longer distances of 35-44km. So if you lose contact via the direct path, when the vessel crosses the convergence zone there is a chance that you'll pick it up again.

At combat start, convergence zones are less important as the game brings you in closer for combat.

Killerfish is absolutely correct.

The following is a little long,so bear with me.

When all of the sound rays are returned to near the surface, they tend to converge into a small region. Therefore the sound pressure level is increased dramatically in this region known as a convergence zones (CZ).

The convergence zone tends to be at large distances, typically 20-30 nm from the source. It is possible to have multiple convergence zones, which will occur at regular intervals. For example, if the first CZ is at 30 nm, the second CZ would be at 60 nm, possibly a third at 90 nm and a fourth at 120 nm (approximately).

Knowing where the CZ's are based on current situation can be determined using plethora of calculations like Sonar DT, FOM, ROD, and SE (Detection Threshold, Transmission Loss, Figure of Merit, Range of the Day, and Signal Excess) which are not displayed in game.

The CZ is only a few miles wide, and therefore, contacts which are acquired through convergence zones tend to appear and disappear quickly.

We can determine that time window using the 3 and 6 minute rules. These rules are used to quickly solve for distance in Nautical Navigation. Basically these rules are used to quickly determining distance traveled in 3 and 6 minutes.

The premise with these rules is that a Nautical Mile (NM) = 2000 yards (yds)
Additionally, 1 knot (kt) = 1 NM / hr = 2000 yds/hr (this is the equivalent to MPH)

For example, if the CZ was 3 nm wide and the contact was travelling at 15 knots, then the 3 minute rule says:

Speed (kts) * 100 = Distance (yds) traveled in 3 minutes.

Using the rule we get:

For 15 knots, 15kts * 100 = 1500 yds

MOVE THE DECIMAL TO THE RIGHT TWO PLACES – ANSWER IS IN DISTANCE TRAVELED IN YARDS DURING THE 3 MINUTES.

Using the above information: 3 nm = 6000 yds, so at 15 kts, the contact would cross the CZ in 12 minutes (4 * 1500 = 6000). The contact would then disappear, and then reappear when/if it entered the next CZ. So the biggest thing the CZ gives you at max range is initial bearing to point and begin the hunt/stalk.

Note that while the contact might be in the CZ for the full 12 minutes, how long the Sonar Tech was able to actively know it was a contact would depend on the Recognition Differential (RD) which is the point that the detection threshold is such that a trained operator should be able to detect contacts with that Signal to Noise Ratio (LS/N) half of the time he hears them. This means that the contact might not be discerned until 6 minutes had passed.

Now you know why I respect all the ST's and FT's out there. They have a difficult and important job.


By the way, the 3 Minute Rule has a corollary called the 6 Minute Rule:

6 Minute Rule:

Speed (kts) / 10 = Distance (NM) traveled in 6 minutes

Example: if traveling 20 knots, the distance you've traveled in 6 minutes is
as follows:

20kts / 10 = 2NM

for 15 knots: 15kts / 10 = 1.5NM

MOVE THE DECIMAL TO THE LEFT ONE PLACE – ANSWER IS IN MILES

Any ST's out there can point out any flaws in my explanation of course, but those are the basics as I remember them.

[LTJGBeam]

Originally Posted by -Pv-

Thanks for the response KF. At those long distances, I pop up the radar for a snapshot since the threat of an answering shot seems fairly low, then deep dive to close.

I'm corrected in that the Manual does mention this on pg 29. When I mentioned page filler, I was commenting on the book not the game.

Added:
This still leaves the original question if it's important to KF to provide the zone count (if there is one) to the user in the interface.
-Pv-

Also, knowing if the CZ Detection is modeled on the Strategic Map would be useful as well.

[Killerfish Games]

Note that Cold Waters only models the first convergence zone.

[LTJGBeam]

Originally Posted by Killerfish Games

Note that Cold Waters only models the first convergence zone.

Thanks! That is good to know. Loving this game!

[Wiz33]

Originally Posted by -Pv-

Thanks for the response KF. At those long distances, I pop up the radar for a snapshot since the threat of an answering shot seems fairly low, then deep dive to close.

I'm corrected in that the Manual does mention this on pg 29. When I mentioned page filler, I was commenting on the book not the game.

Added:
This still leaves the original question if it's important to KF to provide the zone count (if there is one) to the user in the interface.
-Pv-

Radar horizon from the periscope is probably no more than your direct path sonar range. You can use this to calculate your visual and radar range.

http://members.home.nl/7seas/radcalc.htm

[stormrider_sp]

Although I doubt that the current physics actually simulate this.

[-Pv-]

I suspect in the campaign map, nearly everything is object paths and proximity/probability calculations like most games do at the macro level leaving detailed reflection calculations to the combat portion of the 3D sim where it really matters.
-Pv-