Test: Sonar detection range by speed

[lumiere]

How many times you get killed by Udaloy in Basic Training Submarine Operations?
I lost at least as twice as all Virginia-class SSN that USN actually have.

I finally activating God's Eye mode, and watched how Udaloy performs her job.
I found it is almost the case that after detecting torpedo, Udaloy swithes her Ox York Hull sonar in Active, detecting North Carolina... and rest is history.
You will notice that Ox York in active sonar mode could easily detect North Carolina, more than passive sonar mode does.

But how effective active sonar does against modern submarine?
On the first hand, how speed affects sonar detection range?
(with my poor knowledge, I still couldn't figure out how signetures in DB viewer affects)

Based on Tutorial, I made an experiment.

Conditions:
1. Stream Udaloy by heading 0 deg.

2. North Carolina goes toward Udaloy. showing her bow.
(i.e. relative bearing from NC is 0 deg=Front.)

3. Every 1 second, NC corrects her course toward Udaloy.

4. When Udaloy detects NC (by Ox York sonar), Special message shown indicates
the distance between two units.

5. If NC successfully goes under Udaloy, I considered it as "undetectable".

6. I changed throttles of NC and Udaloy, and examined how speed affects detection range of Ox York (Passive/Active).
For Udaloy in creep, NC changes speed every 1kts.

7. When speed of NC is zero, I made a special script. Every 1 second,
NC moves by 0.0001 second longitude (virtually 0.0005nm/sec=1.8kts) westward.

8. Depth of NC is same: -40m/-66ft. (For depth effect, watch here)
For this reason, I didn't check Ox Tail TASS/VDS detection range.
They are very effective for targets in/under thamal layer, but relatively poor at shallow water.
Actually, in this experiment, Ox Tail couldn't detects NC in the most cases. (i.e. it's troublesome[&o])

9. Time Compression is 30 min (1800x). I ignored this time but this may affects the results.

10. I attached test scen. file and result in excel file so that you can try the detection ranges (and correct my mistake) too.

[lumiere]

1. Ox York (Passive)

Sorry for broken line, but each line indicates the speed of Udaloy,
horizontal axis for speed of North Carolina, and vertical axis for detection range (nm).

Observations:
1. The faster NC is, the further Udaloy hears. I thought for years it's no use reducing speed for 1kts, but it does works
(it's pity that I have to set it manually for submarine in patrol mission).

2. When cavitating (for this example, 25kt), detection range dramatically increases.

3. But not vice versa: the faster Udaloy is, it could hear the less.
It should be noted that detection range are not affected by cavitation of the detecting unit.
(However, there is possibility that it's simply because cavitating speed (8kts) is relatively slow)

[lumiere]

1. Ox York (Active)

Sorry again for broken line.

Observations:
1. Detection range model dramatically changes. Imagine that Hull sonar swithes Passive/Active mode.

2. Detection range is much better than passive mode (compare with "(passive) Creep (5)" line) when Udaloy creeps.
Just like passive mode, speed of Udaloy decreases detection range.
it's no use pinging in Full/Flank throttle! (use sprint and drift)

3. However, speed of North Carolina has virtually no effect on detection range.
It depends on only detecting unit's speed.

[ARCNA442]

You did a great job with this

It's fascinating to the exact relationships between speed and detection ranges.

[c3k]

Thanks for showing this.

[Rory Noonan]

Great work!

Speed below 5kt does indeed make a difference, water noise over the hull is part of the model.