Is a depth sounder an altimeter? - SailNet Community

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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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Old 03-28-2010
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Is a depth sounder an altimeter?

This is a silly question, but one I'm afraid I must ask: Will a depth sounder work when you're out of water?

I'm guessing (and hoping) not. I just installed a new triducer and I'm getting temp and speed to my display but the depth reads blanks. In a panic assuming that my new triducer is defective, I tried my back-up depth meter. It too reads blanks. So now I'm somewhat relieved, but still wondering.

Then it hit me, hmmmm, does sonar need water as a medium to read the feedback - it must, right?
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Yes, it needs water.
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The sound doesn't reflect well enough in air for the transducer to be able to pick it up
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An altimeter is a barometer (more or less)... nice idea, but a depth sounder would struggle trying to bounce info off the clouds!
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you can place a steel plate under you transducer and you will get a reading
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Old 03-29-2010
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A large bowl of water under the boat to refect the sound will sometimes work to test the unit. You need to factor in the different speed of sound in air, but I forget what the conversion is.
Be careful operating out of the water for too long as some units (more fishfinders) can overheat
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Seeing as a transducer works fine epoxied to the inside of the hull I don't see how it can overheat out of the water. Humminbird suggests this mounting method as do others.
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In industry we use ultrasonic level detectors all the time... you have to factor in the diff is speed of sound in the medium, and "depth sounders" would be optimized for water, but the technology certainly works both ways.

It wouldn't be an altimeter (ie height above sea level), but more a "height above ground" measurement.
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Quote:
Originally Posted by mitiempo View Post
Seeing as a transducer works fine epoxied to the inside of the hull I don't see how it can overheat out of the water. Humminbird suggests this mounting method as do others.
Structures that conduct sound well are at least reasonable heat conductors which I think protects in hull transducers when the boat is in the water.

I have not seen first hand any damage from operating out of water myself. I am mealy passing on what I have read. A quick google search lead to the following post on another forum. The original poster contacted Airmar (who make most of the transducers used by all companies). The question and reply are listed below.

Question
I have a B260 transducer and would like to know if it is safe to turn on my Simrad CX44e while the boat is out of the water? In the water I can hear the normal clicking while using the (chartplotter only) so I know the transducer is active. Should I remove the transducer cable with the power off so it does not damage the transducer if I want to use the chartplotter while out of the water?


Response

Thank you for contacting AIRMAR Technology Corporation. The transducer should not be harmed if it runs out of water for short periods of time. I would not recommend leaving the transducer running for more than a couple hours. Of course, if you want to play on the safe side just unplug the transducer from the electronics.

Last edited by noelex77; 03-29-2010 at 02:53 PM.
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Old 03-29-2010
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Actually, most depth transducers are about 50k Hz frequency - some are about 200 kHz, and some are both ( ones with a shallow/deep setting) the transducers are tuned to be coupled to water. There are transducers that work in air, but they are of lower frequency, because it takes more energy to transmit through air. At 50 kHz the depth transducer COULD probably transmit and receive through air, but it would need a much higher energy signal, which the depth sounder power supply can't deliver.

It's best wait until the boat is the water to check the xducer. The "bowl of water" idea will not work because there is deadband or a minimum depth that the unit wants to see. Unless maybe a really deep bowl.

Leaving it on in air won't hurt it in the short run, but over time the transducer can mechanically wear out. the surface of the transducer is actually moving 50,000 times a second - it's not moving very far - maybe a couple of microns - but it still moves and can wear.

Best Regards,

e

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