How do you detect surface ship at long range?

[Dron22]

I assumed that because of the noise a ship's screws emit, it should be easy for sensors on a submarine to hear a ship from far away. However I find that I have to get close within 5nm to detect a ship on the broadband sonar display. Of course it's easy to detect a ship from far away when it's constantly ping it's active sonar, but what do you do if it's not?

[Dr.Sid]

5nm sounds like either really bad conditions (storm), or you are under the layer, and the ship is not (obviously). Warship moving at normal speed should be detectable at about 10nm. With good conditions and convergence zones, it would usually be first convergence zone, about 30nm, or even second, 60nm.
Also remember the ships can be first detected on low frequency narrow band sonar. Towed array is best at low frequencies, spherical is worst.

[Dron22]

Thanks, by the under the layer do you mean the thermal layer? How can you find out where the thermal layer is then?
And what is convergence zone? Is it a sonar function to detect ships at 30nm or 60nm?
Is still have not understood how to make use of the narrow band sonar yet, I thought it's for detecting submarines that are travelling on silent running at less than 5 knots.
I was just playing the campaign today, and in the mission where you have to torpedo the Indian Hermes class air craft carrier as a Chinese Kilo Improved sub, I could not hear the air craft carrier from even 15 nm, although the sea was calm and I was only 90 meters deep. I had to use the periscope to find the position of the air craft carrier in the end.

[Hinrich Schwab]

Originally Posted by Dron22

Thanks, by the under the layer do you mean the thermal layer? How can you find out where the thermal layer is then?
And what is convergence zone? Is it a sonar function to detect ships at 30nm or 60nm?
Is still have not understood how to make use of the narrow band sonar yet, I thought it's for detecting submarines that are travelling on silent running at less than 5 knots.
I was just playing the campaign today, and in the mission where you have to torpedo the Indian Hermes class air craft carrier as a Chinese Kilo Improved sub, I could not hear the air craft carrier from even 15 nm, although the sea was calm and I was only 90 meters deep. I had to use the periscope to find the position of the air craft carrier in the end.

The Kilo doesn't exactly have the best sonar package in the game. However, the ship should be detectable from a good way out. Also, 90 meters is definitely deep enough for a thermocline to interfere with sonar, if a thermal layer is present. Check the SSP station's XBT report to see where the thermal layer is. If you are below it, your passive detection drops dramatically.

[Dron22]

Originally Posted by Hinrich Schwab

The Kilo doesn't exactly have the best sonar package in the game. However, the ship should be detectable from a good way out. Also, 90 meters is definitely deep enough for a thermocline to interfere with sonar, if a thermal layer is present. Check the SSP station's XBT report to see where the thermal layer is. If you are below it, your passive detection drops dramatically.

What is the SSP station XBT report?
I can detect some of the ships from a long range if I use the narrow band sonar from a good range. However if I use the broadband sonar I cannot hear any of them even when they are less than 10nm from me. It was the same in missions where I played as an Akula Improved. I stay deep to avoid detection.

[Pisces]

Originally Posted by Dron22

What is the SSP station XBT report?
...

S(ound) S(peed) P(rofile) station (e)X(pendable) B(athy)T(hermograph) report.

Basically it is a temperature sensor that is floated up to the surface. When it reaches the surface it starts to measure the soundspeed as it dives to the bottom. This station (last button of the Sonar station) shows a table and graph of this sound speed change versus depth. A sharp bend in that graph is a location of a layer where soundrays get curved towards lower soundspeeds. But the layer may not be shown on it if the seabed at your current location isn't deep enough. The sensor simply wasn't able to measure it. Depending on the scenario settings there may not even be a layer, just a straight line as the curve.



Convergence zones are circular regions on the surface around the source where sound-rays get focussed after they are emitted deep into the ocean. As they reach further into the depth and penetrate increasing water-pressure they get curved back upwards to the surface. Once they reach the surface the sound can bounce downwards again to repeat the dive and make the 2nd or possible 3rd convergence zone. Assuming the sound was strong enough to be detectable at those ranges.

Subguru's download page (www.subguru.com) should have some documents that explain underwater accoustics a bit. Atleast enough to the extent that 688i Fast Attack, Subcommand and DW simulate it.

The following link may be too technical, but does show how sounds curve based on the shape of the sound speed curve:

http://www.fas.org/man/dod-101/navy/...P/snr_prop.htm

[Kaye T. Bai]

Personally, I like to use ESM for ASUW contacts at long distances. Good luck with in your future missions!

[Dron22]

ESM is good, but the problem is that it's not accurate in respect of the distance and you have to stay at periscope death to keep track of your contacts.