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Old 08-07-2012, 13:21   #1
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Hydrophones

No, Micah the Maritime Madman has not been sampling the Jamaican Dream Shrubbery.

The main purpose would be an extra sense for detecting boat-eating things like breakers on a reef, or rapidly approaching lookoutless freighters when the other senses are dulled/inactive.....such as fog, darkness, or those moments where one is forced to sleep.

An interesting side-benefit would be the ability to listen in on whale's songs.

My questions are: Anyone got one of these things, or heard of one, or have any tips that would make a cheap and effective system?

I'm averse to having potentially leaky holes in the hull and presenting Stowaway Murphy with any more toys than absolutely necessary, so a trainable transducer head for narrowing down a source-bearing would have to be either solid state (non-mechanical) and through the hull material, or a deployable head over the side (eg such as windvanes already are).

In this line of thinking, a suitable microphone, amplifier and interface (speaker....headphones.....recording device....computer program for analysis/auto-classification/filtering etc etc) shouldn't be all that hard to bodgy together from off-the-shelf parts.

Is there potential, or is it time for the canvas jacket and the rubberised seaberth for poor old micah? Thoughts?
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Old 08-07-2012, 13:44   #2
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Re: Hydrophones

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Originally Posted by micah719 View Post
No, Micah the Maritime Madman has not been sampling the Jamaican Dream Shrubbery.

The main purpose would be an extra sense for detecting boat-eating things like breakers on a reef, or rapidly approaching lookoutless freighters when the other senses are dulled/inactive.....such as fog, darkness, or those moments where one is forced to sleep.

An interesting side-benefit would be the ability to listen in on whale's songs.

My questions are: Anyone got one of these things, or heard of one, or have any tips that would make a cheap and effective system?

I'm averse to having potentially leaky holes in the hull and presenting Stowaway Murphy with any more toys than absolutely necessary, so a trainable transducer head for narrowing down a source-bearing would have to be either solid state (non-mechanical) and through the hull material, or a deployable head over the side (eg such as windvanes already are).

In this line of thinking, a suitable microphone, amplifier and interface (speaker....headphones.....recording device....computer program for analysis/auto-classification/filtering etc etc) shouldn't be all that hard to bodgy together from off-the-shelf parts.

Is there potential, or is it time for the canvas jacket and the rubberised seaberth for poor old micah? Thoughts?
THANKS! For reminding me. Thought about this a while ago then forgot again, but just ordered one of these..
Contact Mic Piezo Pickup with 1/4" Jack Socket | eBay
I have a steel hull so hopefully can just stick it on and plug into a little mic amp then the hifi radio.
Should work on a GRP hull as well??
WOuld be interesting though. Nearly bought a stethoscope a while ago but have you seen how much they cost!

Will post again when it turns up.
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Old 08-07-2012, 13:54   #3
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Re: Hydrophones

Cool....5 quid is my kind of R&D budget! Wonder if two of them would work with stereo speakers...or 4 to go full surround? Need an electronics whiz to chip in some thinkings......
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Old 08-07-2012, 14:13   #4
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Re: Hydrophones

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Originally Posted by micah719 View Post
Cool....5 quid is my kind of R&D budget! Wonder if two of them would work with stereo speakers...or 4 to go full surround? Need an electronics whiz to chip in some thinkings......


Wonder if they work both ways? Wind up some dolphins...
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Old 08-07-2012, 14:31   #5
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Re: Hydrophones

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Wonder if they work both ways? Wind up some dolphins...
Careful, you might have a Whale getting amorous with your boat, or confusing you for the competition. Yikes! A jilted 50 ton suitor, or a jealous 50 ton spouse, or much, much worse....
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Old 08-07-2012, 14:43   #6
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Re: Hydrophones

The main problem would be detection range, depth of the microphone mounting, directional control, filtering out ambient noise, interference from own boat generated noise, and training. Most systems are highly complex and to be useful have to be manned round the clock. If you are getting into shallows, you are best off with a depth finder and radar than listening for breakers on a reef. Same if you want to detect prop noises from other vessels. It takes a good deal of training to determine speed of closure once you have a contact established. For the most part, you might detect a merchant ship of some sort at long range, and you might be able to estimate if it is closing, maintaining the same range, or moving away, but as far as determining range, you are essentially making a guess. You would be much better off with an AIS system which can be set to sound an alarm if another vessel with AIS is getting too close and a radar alarm for vessels not equipped with AIS.

Finally, if you have the microphones (and you need more than one to cover different sectors and a means to switch between them to give you a bearing) mounted on the hull of a 40-50ft sail boat or motor cruiser, you will likely not be able to mount them far enough below the surface to minimized sounds generated by the hull and water surface. In that case you will need to use a towed array to get the microphones deep enough to be of some help.

If one just wants to listen to whale song or other biologics, go for it, but in my opinion you will be better off with good charts or chart plotter, a good means of finding your location, a depth finder or fathometer, and radar backed up by an AIS system if you want to rest easily when not at the helm.
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Old 08-07-2012, 15:09   #7
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Re: Hydrophones

Dunnit

Remembered i had a little piezo buzzer which, being a transducer also acts as a mic.

So that stuck to the hull with some silicon is now going through a guitar preamp into the radio.

Can´t hear anything apart from me walking about the boat, but can make the hull feedback if i turn it up loud enough

Probably next to useless for detecting reefs or big ships but as a next pointless project it´s fun
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Old 08-07-2012, 15:15   #8
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Re: Hydrophones

Hi, I have had a hydrophone on Gilana for about 10 years. It is good fun. Sometimes you can hear amazing things. Once in Bermuda anchorage we heard a domestic argument on a nearby sailboat. There is sound processing software that will give you a visual representation too. We use "frequency analyzer" our mic is an electret condenser one, cheapie salvaged from an old tape deck. Took the felt cover off the front, made a case out of a film canister, filled with oil and dropped in our bilge sump. Added a gal of water to cover it and that was all. Works like a charm.
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Old 08-07-2012, 15:23   #9
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Re: Hydrophones

I would wonder about the sensitivity of your piezoelectric transducer. In amplifying it to the point where you'd be able to hear anything you'd be also amplifying every thing that vibrated your hull. Think about the ones that are audible, waves slapping the hull, any flotsam the contacted and so forth, those signals would have to be filtered out or a massive compression algorithm with a very fast attack applied to prevent them from destroying your equipment. Obviously it is possible to pick up sound waves of very low energy through the hull since the transducer for your depth sounder is doing so but it uses a very specific frequency and doesn't pay any attention to the rest and isn't trying to make those signals audible.

A microphone can be waterproofed and used under water but since they generate the electrical signal by moving a diaphragm in an magnetic field the waterproofing will produce a muffled signal.

What you really want is a hydrophone. They generally use piezoelectrics, which produce electricity when a differentiating pressure is applied to them, and so can produce a clear signal. Just don't use them as your lead.



Sounds like fun!
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Old 08-07-2012, 15:31   #10
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Re: Hydrophones

Quote:
For the most part, you might detect a merchant ship of some sort at long range, and you might be able to estimate if it is closing, maintaining the same range, or moving away, but as far as determining range, you are essentially making a guess
Even that would be a help in fog if I have no radar or AIS, or as a backup if I have them but they fail...and I understand and agree with all the other caveats you mention. For the outlay of pocket change or bits of stuff already laying about and using redneck tech, I thought it would be worth at least a look or a try. Any input is welcome!

Btw, the AIS is only good for folks with transponders/receivers/plotters, and eyes on screen, isn't it? Anything that can help me keep out of the way of stuff is worth a shot.

Thanks for the input, and thanks conachair for your time. Keep me posted on how the experiments turn out?
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Old 08-07-2012, 15:52   #11
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Re: Hydrophones

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There is sound processing software that will give you a visual representation too. We use "frequency analyzer"
That would be the possible fix for cheap & effective filtering. If I'm interested in a certain frequency range, such as the giant props of sailboat-eating freighters, it should be possible to set an alarm to that, within upper and lower limits of volume. I don't need a firing solution, just enough warning that there be iron monsters out there within squishing distance! Useless in a busy channel, but out in places where one would risk a nap it might be a useful and dirt cheap backup to the egg timer....

As to bearings....I'd experiment with fore & aft locations for a simple pair of mic's to get the biggest baseline for a triangulation, even if it is as simple as running the signals through stereo speakers. Maximum practical sensitivity as to direction, though without at least a third mic I'd have to flip a coin as to port vs starboard. One problem I see cropping up is that the hull might cancel all that out by acting as a giant eardrum. Got to be a way to sort that out, perhaps the software filtering approach. Failing that, go external. External mic's raise some problems, such as flow noise, shorts, corrosion, fouling, impacts, drag and all the other things that make boats so wonderfully interesting and fun. Towed array might be getting too serious, unless I can hang a lure off the end and at least have that benefit.....
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Old 08-07-2012, 16:45   #12
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Re: Hydrophones

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Originally Posted by micah719 View Post

Btw, the AIS is only good for folks with transponders/receivers/plotters, and eyes on screen, isn't it? Anything that can help me keep out of the way of stuff is worth a shot.

Thanks for the input, and thanks conachair for your time. Keep me posted on how the experiments turn out?
As for AIS, the nasa standalone unit isn't massively expensive and has an alarm which easily wakes me up offshore when anything is within the alarm zone, I usually set it to 5 miles. Draws next to no power as well.
http://www.nasamarine.com/proddetail.php?prod=AIS_radar

Will be interesting to see if the ebay transducer is better than the cheapo buzzer from maplins, shall update when it arrives. All good fun
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Old 08-07-2012, 17:14   #13
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Re: Hydrophones

I'm all ears!
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Old 09-07-2012, 06:39   #14
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Re: Hydrophones

BTW, I would not use it for Navigation purposes. Its just for fun. You need huge money for a serious passive system.
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Old 27-08-2012, 08:51   #15
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Re: Hydrophones

Two publications from the USN with detailed info about WW2-era sonar. Includes circuit diagrams. A major advance over reinventing it all from scratch.

Naval Sonar

The Fleet Type Submarine - Submarine Sonar Operator's Manual
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