Using sound underwater

sarabande

sarabande

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If I attach a couple of 50W speakers directly to the hull of the boat, can I use them to entice dolphins/whales etc, by playing calls, or alternatively use them as a defence mechanism against Russian frogmen and orcas ?

Not entirely frivolous, there's a serious idea behind the question.
 
sarabande said:
If I attach a couple of 50W speakers directly to the hull of the boat, can I use them to entice dolphins/whales etc, by playing calls, or alternatively use them as a defence mechanism against Russian frogmen and orcas ?

Not entirely frivolous, there's a serious idea behind the question.
Click to expand...

Dangerous idea. Get it wrong and you could be attacked by an orca thinking you are a seal or torpedoed by a Russian ship thinking you are a Royal Navy diver.
 
While I can understand the whale thing, you muddled it with worrying about Ruskies.
Sound travels a lot faster in water, so you can talk to your friends a bit quicker.

The serious idea bit interests me.
Just looked. Difference is 4.3 times the speed in air. Does that help??
 
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Most cetaceans are protected under a range of Eu and Uk Law, which prohibits deliberate disturbance particularly during the breeding season. You might well find that in order to deliberately attempt to 'speak' to them you would need a Licence from MMO which would only be issued if you can justify the research you are presumably attempting.

I would also be a bit worried about attracting the attention of a creature considerably larger and heavier than my boat, without being fairly certain I wasnt giving whatever the whale equivalent of a two fingered 'go away' is, and getting a similarly robust response from it!

. Simiarly the thought of unwittingly enticing some Orca to have it off with my boat leaves me cold!
 
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I was visiting a moored boat to inspect a poorly anchor winch, turned out it had a badly worn gearbox and made a horrendous noise. during a test the skipper called us all to silence as there were 3 large dolphins coming directly at the boat. soon as the noise stopped, the dolphins buggered off back to the pod which were passing a few hundred yards away.
My guess is we were being visited by "the lads" potentially in need of "sorting out".
Moral is, no need for huge speakers (50W in water is bloody loud), just a strange and new noise and the buggers will come visit.

What might be more fun is a directional hydrophone to find where they are.
 
Once off Gorey, Jersey we saw dolphins ( our first time ) a mile or so away so I turned on the depthsounder; they instantly came at us like torpedos, I bottled out and turned it off when they were close but of course they only come to play - as Old Harry says I'd be wary of trying it with bigger things like Pilot Whales or Basking Sharks though they just seem oblivious to boats unless hassled - and certainly not with the BIG proper shark we once saw off Salcombe.
 
sarabande said:
DIY hydrophone..... in fog, sticking a pole with a directional microphone over the side and obtaining the bearing of an approaching motor vessel.
Click to expand...

Directional microphone which works in water may be the issue.
Mr Rayleigh's criterion will be a limiting factor.
The increased speed of souns in water also increases the wavelength.
Passive sonar has a long history.
And long arrays of sensors.
 
I know that sounds travels "better" underwater. All I need is a reliable bearing of the underwater source, in contrast with the less reliable direction of airborne sound. If I stick a waterproof mike on a pole, and rotate it, I should be able to Locate the source.

(I don't want to go to stages 2 and 3 of Identify and Destroy !)


http://dolphinear.com/products.html seems like a starter.
 
Why do you imagine this hasn't been done before?

The fundamentals of wave theory make small directional microphones a bit of a challenge.
 
There is a quite a lot of pleasure in the challenge of doing things from basics. As is raising an idea and seeing if it is workable, and wandering rhrough the background to see if it has 'previous'.

Hydrophones on a small scale suitable for boats ? Perhaps a sort of parabolic reflector ? All i need is

1 a signal that there is a vessel making way. A guess from the frequency/harmonics of the sound to indicate possible size.

2 some form of directional steering of the mike to identify relative angle of max gain. I did this with gonio loops decades ago for air beacons.

Would a couple of mikes , say 50 cm apart be able to resolve the time difference in arrival of one of the long wavelengths you mentioned. Speed of sound in water ~= 1,484 m/s in water; speed of signal in a circuit seems to vary with frequency, e.g.

Freq..............millisec/km
1Khz.................0,072
10kHz...............0.531
100kHz.............3.327

Just digging around to see if a processor could log the difference and if so, how that delta might be used.
 
I think you just invented 'sonar' ........as in SOund Navigation And Ranging.

Now let me think.... I'm sure there's an application for that, somewhere. There could even be a movie in it.
 
zoidberg said:
I think you just invented 'sonar' ........as in SOund Navigation And Ranging.
Click to expand...


No, Sarabande's System is a passive, detection-only system. I don't want to go round pinging from a huge bow appendage to see where I am going or what is coming towards me.

A means of listening for approaching shipping, and giving a rough bearing to within, say, 5 degrees.
 
Can't help thinking, even billion-dollar subs or warships with passive towed array sonars have a job doing that, what with water conditions, thermocline, lots of other factors - but spiffing idea if you can get it to work.

A1 Sailor what do you think ?
 
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