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ChrisPhoenix 10-03-2019 09:53 AM

Hydrophone Distance Estimation
Greetings fellow Kaleuns!

I am trying to become a better hydrophone operator. So i was wondering if there is any "rule of thumb" or anything like "a gain of 3 means around 5000m". Basically i am looking for a quick but simple way to estimate the distance to the target as accurate as possible but in the shortest amound of time. Methods like the four bearings-method are never used in our missions. So maybe you guys can help me out with your experience?

thanks in advance!

Chris Phoenix

Pisces 10-03-2019 10:25 AM

You might want to search the WP discord server. There have been plenty rules of thumb postulated for that. But the problem is, different unit might have different source levels. So you might think X gain is Y far, but it could actually be further or closer. That's why I don't bother. It's also not that neccesary. Just point the bow at the sound and go full speed on the surface. They will appear soon enough out of the mist.

Superesse 10-04-2019 01:04 AM

Regarding steaming towards the convoy and finally they appear. Doesnít that only work in clear weather or slightly cloudy (I donít remember the terms)? If itís foggy you cannot do that, right? Because you wonít see the convoy until youíre dangerously close? Iíve never tried fog yet, so itís just a guess.

About distance checking. I am poor at it myself. But I think you need to be close enough to distinguish a single ship, then count the propeller rotational speed (because I assume that affects sound level?) and then based on the combination of gain and propeller speed calculate the distance (I donít know how). This is only my guess.

Lost At Sea 10-04-2019 01:45 AM

I would also love to know how to do that!
By the time I managed to fumble my way through the four bearings-method the convoy has usually reached Rio de Janeiro... :doh:


ChrisPhoenix 10-04-2019 04:10 AM

The Discord Channel is a little messy in terms of finding information in my opinion. I rejoined it, read thourgh some stuff but hard to find anything. There is just too much going on.

Just heading towards the convoy is fine for the most situations sure, but i would also like to be able to know if a destroyer is at safe distance to surface by just relying on the hydrophone for example.

Of course i don't want to say "alright contact is exactly 5435m away." But plus or minus a 1000 meters would be nice to know.

Pisces 10-04-2019 06:32 AM

It should be safe if you do a periscope check before you surface. Should be standard procedure anyway.

Yes, discord is messy. But you should be able to search the channels for keywords. Rule seems to fit as one.

ChrisPhoenix 10-04-2019 10:07 AM

I didn't know you could do that. :o That actually helps a lot! Thank you.

Pisces 10-04-2019 10:43 AM

As for foggy conditions, yeah, you better be on your toes and pay attention. Make sure the deck-watch is doing it's job. Either slow down and turn away at the first sight, or immediately dive. Or both. Or don't go fast in the first place. Oh heck, do all to be sure.

Superesse 10-05-2019 06:44 AM

Slow down AND dive is not a good idea, right? 😁

Pisces 10-05-2019 06:51 AM

Dive might take longer as you slow down, but you don't decrease distance as much either. At 18 knots you move 9.36m per second. Also, if you can retreat into the fog again, you stand a better chance of escaping than being submerged (until radar becomes a thing)

ChrisPhoenix 10-05-2019 02:28 PM

I actually picked up some things from Discord now. I have yet to test them tho. Regarding distance to destroyers: i'd rather not stick my periscope out if i'm not 100% sure he is far enough away. That's why i'm trying to do it with hydrophone. Better stay deep...

Regarding Diving speed: I only go full speed while diving when the alarm bell rings. Which is only when we are spotted at the moment. Copied that from Silent hunter, where alarm automatically meant full speed. In any other situation i'd rather dive slowly, because it is much easier to stabilise the boat when you do it slower. Going full speed and maintain periscope depth is rather hard.

Pisces 10-05-2019 02:50 PM

If the direction to the destroyer is not moving you can be reasonable assured it is far away (or still homing in to you ;) ). If it drifts noticeably in degrees while you are listening, then it is probably quite close. And if you don't pop your periscope too high (just crossing the waterlevel, still in the waves) then you should be able to see it's smoke and know you should be on your guard.

For crash dives you also better have your negative tank filled beforehand. I never said you should stay at full throttle. Once you are under you are clear and can do whatever you think is needed. Just be sure to leave halve of a tick in the negative tank, as that puts you better neutrally buoyant. (That is, until next week as they are bugfixing buoyancy stuff they said. So next weekend all could be new again.)

ChrisPhoenix 10-06-2019 03:10 PM

Yes the boyancy update will most likely change everything. And i personally can't wait because i am waiting for a trim tank since the very beginning...

I also hope they add rough seas and make the boat a little more shaky in the water. But the trim tank alone will make this update awesome.

Fanders 10-27-2019 04:37 PM

Hi everyone!

I just did some data collection with the hydrophone in tutorial mode (where you can se the other ships distance and bearing on the map).
I focused the hydrophone in the exact vector to the target, then I turned the gain knob to the point that the sound turned into distorsion. At that point I collected the distance of the target from the map.

I plotted the data in google sheets and found out that the relationship between the gain and the distance is linear.
Thats quite strange btw, because the sound preassure should decrease with the square of the distance.

One more thing that was a bit strange is that gain level of 2 seems to be the limit. There was no point lowering the gain below 2 -no matter how close i got to the target.


from the data colleced i managed to make a trendline/regression curve of the plot. In my website below you can download the pdf of the diagram i did and use if you want!

Of course this could be done with more precision, but i think its a good diagram to use for rough estimations!


PeterS 10-31-2019 10:12 AM

Thanks for your work on this! What were your settings for high and low pass filters? I suppose these need to be identitcal to compare the results with your diagram.

Personally I found 1 and 8 pretty reasonable filter settings.

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