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Old 12-05-2007, 13:26   #1
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Depth transducer

I have been searching mfg websites about these depth transducers that are mounted inside the hull and trasmit through the fiberglass. Alas, there is always an info overload on what the instrument will do, but next to nothing about the transducers. So, my questions are these: does it matter how much thick the fiberglass is? I presume it will redce perfomance, but depths over 60' or so are not really important. Is it OK to mount one on the centerline of the boat where the outside of the hull has a bend? If you mount one off-center, will it work properly even though the outside of the hull is sloping? Some are called something like "22 degree transducer". Does this mean that the beam goes down at 22 deg from the face of the transducer so that when you mount it flat against the sloping side of the hull it will shoot more or less straight down? Yeah, I know that the thru-hull type are better, but that's not an option as it would be silly to spend $400 hauling out the boat for a $75 transducer.

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Old 12-05-2007, 19:24   #2
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22 degrees is the effective output angle of the pulse. 11 degrees each side of center.
Mount it facing straight down wherever you mount it.
Google around for a diagram and instructions.

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Old 12-05-2007, 20:09   #3
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Airmar is the manufacturer of transducers for almost all manufacturers of depth sounders. You can call them and their tech support folks will answer all of your questions.

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Old 12-05-2007, 21:59   #4
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The "shot" angle is determined by the frequency used. You will usually have a choice of 50Khz, 125Khz and 200Khz.
Any transducer can be mounted inside a glass hull. There are two methods. One is to build a box and fit the transducer inside it. Then fill the box with oil. The other is to epoxy the transducer directly to the hull. I have had success with both methods.
The glass hull will attenuate the signal to some degree. The thicker the hull, the more it is attenuated. But it is not so much that it will render you finder useless in 60ft or less. You will still have very good soundings down to a considerable depth.
The only possible problem you could have is an air void in the glass layup. These days that should be rare. The easy way to check is to place a grease like substance like KY gell on the transducer and place it where you want to mount it. That way you can test to insure it sends through the hull OK. Then bond it down. The ease of using Epoxy is that you can either use a ready nmade thick glue, or add a thickening agent to resin and then you can place the transducer on the hull at the angle you want it to aim straight down.
The only other comment I can make is to make sure you are not sitting over or too close to a keel. If it is too close, you can get eroneouse readings bouncing off the keel. Once the sounder gets into too deep a water, the sounder will lock onto the keel reflection and give you a false reading. The danger is, this reading may not be just a foot or two as the keel maybe away from transducer. The reflection can sometimes be something much different and you maybe fooled into thinking you are good water depth till it shallow enough for the sounder to once again lock onto the bottom and then it maybe to late.

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Old 12-05-2007, 23:10   #5
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Originally Posted by Thermal
Yeah, I know that the thru-hull type are better, but that's not an option as it would be silly to spend $400 hauling out the boat for a $75 transducer.
Yo Therm,

there is no need to spend an EXTRA $400 for a haulout to get a proper installation.

If this installation cannot wait for the next normally-scheduled haulout, it can be done in the water with the help of a diver with this experience. The whole thing will take about 5-10 minutes of the diver's time.

The transducer must be mounted perfectly plumb, using custom-fitted fairing block inside and out, so preparation is only everything. Locate according to manufacturer's instructions, usually forward of any thruhulls which could create turbulence, and far enough away from the keel to avoid its' shadow. Forward of the keel if possible. Some fiberglass boats have a level "boss" moulded right in the center of the boat, just forward of the keel for just this very purpose.

best, andy
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Old 13-05-2007, 01:30   #6
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A "Tilted Element" transducer, with "Beam Angle" in yellow.
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