What do we hear in hydrophones?

[Alex Paen (ljekio)]

The question has long been of interest: how plausible are the prop noises that we hear in hydrophones?
I have never rotated a real hydrophone, but for example in silent hunters it sounded completely different. Moreover, there is a clear difference between warships and merchants, and what I read, it was written everywhere that they were distinguished not only by category, but also by type, based on the RPM and the number of blades on the props. Measuring the RPM was quite fun, and you could get a rough idea of ​​the speed. Our sonarman does this and gives approximate range reports, but can we try it ourselves? I’m not talking now about the oddities with the lack of bearing without the required sonarman skill, like about the hydrophone dial, on which nothing is visible.

[Micullus]

Yes you can do it all by yourself !

To estimate speed you got to count the pulses:
Listen to the pattern and you hear a "ROCK... tock... tock... tock..."
Thats a 4 blade propeller, common on traders.

You count the rocks for 10 seconds and multiply by the number of blades...
After that you divide it by 4,1 and you get the speed in knots.

Distance is trickier. If you can hear them on the high filter it means you are less then 15 km away.

Edit: For the angle ... the outer ring on the hydrophone gives you the indication in grad.
The others are not important. If you cant read it use the free cam (N) or try bigger textures. I use the 2nd lowest texture setting and it's already readable.

[DECAFBAD]

Real ships sound like this (if you're lucky you'll hear some whales too):
Lime Kiln hydrophone live stream
https://pro.stream101.com/player2/?ip=2&port=8047&username=smrucons

[Janov [GER]]

I am sure that todays hydrophones on modern submarines with computer-assisted analysis are able to distinguish all sorts of signals...and maybe very experienced operators in WW2 could make some educated guesses, too.
But I believe a 3-bladed prop at 100 rpm will sound exactly the same as a 4 blade prop at 75 rpm. And even if you knew the count of blades and could therefore deduce rpm, the resultant speed of a ship would be a function of it´s draft and also the sea state.
So I believe that a "realistic" assessment of a ships noise will probably be limited to a rough bearing, even rougher range and maybe an estimate of speed.

[DECAFBAD]

You can hear many noises on a ship. Only on freshly built or recently overhauled modern ships is it impossible to tell the number of blades by ear. Other than the propeller beat there are rhythmic noises associated with the propeller shaft and the main engines. Close up you hear the steam engine chug. You may hear the shaft squeak due to imperfections. The propeller might be imperfectly finished so even that could be a dead giveaway: one blade is louder as it passes the hull. This would be especially true for mass-produced ships such those of the Victory class which would sometimes compromise on the quality of the outcome.

[Alex Paen (ljekio)]

Thanks for the responses guys.
I was prompted to create this topic by some unnaturalistic sounds in the hydrophone in UBOAT. In addition to the fact that I hear everything with a barrel effect, often during a pursuit I can hear several overlapping escort props and they are damn same, and have a characteristic phaser effect in many cases. This means that the same sound wave operates on all of them, with almost no difference in RPM and frequency. Although Flower and Tribal not may sound the same in my opinion.

[DECAFBAD]

Though it can be improved, as it stands I think UBOAT presents the best hydrophone model of subsim games. Other than Dangerous Waters of course but that's almost a different genre.

[Micullus]

Originally posted by DECAFBAD:

You can hear many noises on a ship. Only on freshly built or recently overhauled modern ships is it impossible to tell the number of blades by ear. Other than the propeller beat there are rhythmic noises associated with the propeller shaft and the main engines. Close up you hear the steam engine chug. You may hear the shaft squeak due to imperfections. The propeller might be imperfectly cut so even that could be a dead giveaway: one blade is louder as it passes the hull. This would be especially true for mass-produced ships such those of the Victory class which would sometimes compromise on the quality of the outcome.

Watch this Beautiful old Lady.... thats the sound of love....

https://youtu.be/8HFStCaVEBo

I's so cute when she wiggles her bum

[Twelvefield]

I remember reading from a book on American WWII subs that they would hold hydrophone drills, and the commander would wipe a shaving brush on a microphone to simulate underwater screw sounds. Owning a shaving brush myself, I decided to try it and it works. It's comparable to the hydrophones they would have used back then.

As for phased sounds, that's not out of the ordinary. We hear phased sound waves all the time, we just tend to ignore them. It's possible that the game overdoes the phase effect because of the limitations of the audio engine, but it's not wholly improbable that those sounds would be realistic.

And as for modern hydrophones, you'd need some Navy expertise, there, ask Jonesy. All I can say is that for Christmas one year I bought for my wife the Littmann Cardiology IV stethoscope. It has a computer-designed sound bell, and uses algorithms to enhance audio. Listening with her old stethoscope from pre-millennium and the LCIV, it's the difference between the kid next door banging Baby Shark on a garbage can versus the Vienna Philharmonic playing Carmina Burana. If the Navy has comparable technology, then we should all be speaking in whispers if we don't want to be overheard, even in Saskatchewan.

[DECAFBAD]

What's pretty close to a modern passive Sonar that you can get is a conference room microphone - the ceiling mount ones that cost $3000 have the same tech that subs had in the 1980's, and they're based on the same principles as the GHG: lagline bearmforming.
Now getting this working in the game would not be easy but also it would not be impossible. My implementation of the GHG (shameless plug: https://github.com/mygamingaccount/ghg-hydrophone-demo) can output a Unity DSP module. It eats CPU time like kids eat candy at Halloween, but I was able to ramp up the effect to 80 sound sources. And that was while it was running in the browser. So ahem, for your consideration

[Alex Paen (ljekio)]

Originally posted by Twelvefield:

As for phased sounds, that's not out of the ordinary. We hear phased sound waves all the time, we just tend to ignore them. It's possible that the game overdoes the phase effect because of the limitations of the audio engine, but it's not wholly improbable that those sounds would be realistic.

Anyone who has ever worked with sound knows how easy it is to make a phaser from two identical sounds. But since in real life there are no sounds that are completely identical in everything, then this effect will not be so striking. As soon as you make some changes to one of them, the phaser will immediately disappear. And here we have five warships that can chug-chug in exactly the same way to the point of indistinguishability.

[Alex Paen (ljekio)]

Originally posted by Janov GER:

I am sure that todays hydrophones on modern submarines with computer-assisted analysis are able to distinguish all sorts of signals...and maybe very experienced operators in WW2 could make some educated guesses, too.
But I believe a 3-bladed prop at 100 rpm will sound exactly the same as a 4 blade prop at 75 rpm. And even if you knew the count of blades and could therefore deduce rpm, the resultant speed of a ship would be a function of it´s draft and also the sea state.
So I believe that a "realistic" assessment of a ships noise will probably be limited to a rough bearing, even rougher range and maybe an estimate of speed.

It turns out that all these things and exercises were invented exclusively by simmers?
https://steamuserimages-a.akamaihd.net/ugc/2039600735586876479/30E528D0FBB1546EAAF86598FAC0A383FC0793A7/
Because if this is not so, then it is generally not clear how they can be distinguished. But they distinguished quite successfully, although inaccurately.

[DECAFBAD]

Maybe my comment was too long. Here's a tl;dr: you hear the number of blades. On brand new container ships made in 2024 you might not hear it.