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Author Topic:   Transducer out of the water
mikemdd posted 08-09-2009 02:32 PM ET (US)   Profile for mikemdd   Send Email to mikemdd  
The transducer on my 160 Dauntless (transom mounted/Lowrance 520C) creates signficant rooster tails and splashing at speeds over about 30 mph. I always have the unit on for measurements other than depth. Would it hurt the unit to tip the transducer out of the water when depth measurements are not needed, but with the main unit still energized?


Nauti Tauk posted 08-09-2009 08:52 PM ET (US)     Profile for Nauti Tauk  Send Email to Nauti Tauk     
You should adjust the transducer , probably up, until you get minimal spray. Some transducers produce more spray than others but they all can be raised/lowered, angle added or removed to reduce spray at higher speeds. I personally have Lowrance Skimmer transducer that produces very little spray all the way to WOT and 42+ mph maintaining a good readout. Read the installation manual for your particular unit to find out what the manufacturer recommends as the optimal installation height. The unit should remain in the down position.
mikemdd posted 08-10-2009 10:48 AM ET (US)     Profile for mikemdd  Send Email to mikemdd     
I checked the owners manual and it does not say anything about being energized without the transducer in the water (ie shooting through the air). Given that you can apparently shoot through the hull with these transducers ("skimmers"), I am drawing the conclusion that tipping it up out of the water when not being used (but energized) should not be a problem.


jimh posted 08-10-2009 01:26 PM ET (US)     Profile for jimh  Send Email to jimh     
Think of the piezo-electric element in the SONAR transducer like a drum with a drum skin. The electrical excitation of the transducer is like striking the drum skin with a drum stick. When the transducer is immersed in the water, the piezo-electric element is coupled to the water, and the energy of the vibration created from the exciting pulse is coupled into the water. In the drum analogy it would be like filling the drum with an old blanket or other material to absorb to energy of the impact.

When you excite the transducer when it is out of the water, there is no dampening from the coupling to the water. The element may experience more excursion than normal. It is hard to say in the long run if this would damage the element.

In any case, you ought to look for a remedy to the spray which does not involve fiddling with the transducer mounting every time you transition your boat to plane from slow speed. That is a wearisome way to cure the problem.

Nauti Tauk posted 08-10-2009 04:55 PM ET (US)     Profile for Nauti Tauk  Send Email to Nauti Tauk     
Let me try one more time. If you mount the transducer correctly you won't have a spray problem. When properly mounted and adjusted tilting it out of the water would not be needed. You can download proper mounitng of the transducer from the site.
Mr T posted 08-10-2009 08:24 PM ET (US)     Profile for Mr T  Send Email to Mr T     
Ditto to what Jim said, the element is cast in with epoxy by the factory once aligned. If you run the power on with it out of the water, the element will delaminate from the epoxy and you will problems with readings. If you have power to it, you will need to have it in contact with the water.
mikemdd posted 08-10-2009 09:37 PM ET (US)     Profile for mikemdd  Send Email to mikemdd     
The transducer is mounted flush with the bottom of the boat, as the instructions said, and works perfectly at lower speeds. HOwever, for whatever reason, it still gives too much spray at higher speeds. I tried adjusting it in the mounting slots, but the adjustment amount did not fix the problem. With regards to the use out of water, it seems it is not a good idea, based on the technical commments above. It is still somewhat unclear how the transducer works out of the water when using a "through the hull" mounting. Perhaps it is because it is shooting through dense material (ie fiberglass, water) rather than air.


jimh posted 08-11-2009 03:25 AM ET (US)     Profile for jimh  Send Email to jimh     
The acoustical impedance of air as a transmission medium for ultrasonic waves is vastly different than water or a solid structure like a dense fiberglass laminated boat hull. SONAR transducers which are mounted as in-hull transducers are usually coupled either via a water column or via being cemented in place with epoxy. The signals from an in-hull transducer do not pass through air.

The basis for SONAR is that acoustic waves will be reflected when they encounter a change in the acoustic impedance of the propagation medium. This is why you get a reflection from a fish or from the bottom. If a SONAR transducer fires into air, all you get is a reflection, and no signal or a very much attenuated signal is propagated through the air gap.

Some transducers designs create more spray than others. If you cannot find a location on the transom and a mounting height which minimizes spray while providing good SONAR performance, you may have to resort to installing a spray shield above the transducer to deflect the spray away from the motor and transom.

Phil T posted 08-11-2009 08:44 AM ET (US)     Profile for Phil T  Send Email to Phil T     
Mike -

On many transducers, the mounting bracket has slots in which the screw sits for minor adjustment. Try loosening the screws, raising it slightly and retesting. Remember to reseal the screws with a good marine sealant (i.e. Boat Life et. al., not an adhesive like 3m 5200)

Many members have commented on spray from their transducers. One or more have even fabricated a spray shield to knock it down.

mikemdd posted 08-11-2009 12:18 PM ET (US)     Profile for mikemdd  Send Email to mikemdd     
Thanks for the suggestion. As you noted, there are slots for minor adjustment (up/down). Unfortunately, the adjustment was not enough to solve the issue. I could raise the entire mounting bracket, but that would involve drilling new holes and would likely put the transducer too high to work appropriately. The idea of the shield you and others suggested is my next step. A quick search gave me some ideas. Thanks to everyone for your collective help.


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