Permanent depthsounder transducer mounting without through hulls

Posted By: Ramblin' Rod
Date: 10/23/00 9:23p.m.

Report: outside forum guidelines

When coupling an ultrasonic transducer to a transmission medium, ensure maximum energy transfer is achieved by matching the acoustic impedance of the transducer with that of the transmission medium without significantly altering the transducer resonant frequency, or causing the ultrasonic energy to be dispersed off-axis or absorbed. For maximum signal strength the ultrasonic energy axis of transmission must be perpendicular to the reflective surface monitored. That's the technical gobbledegook. This is the procedure I used to mount my Eagle fishfinder transducer: (This tends to sound a lot more complicated than it really is). 1. Test the system by immersing the transducer in water over the side of the boat. Observe the depth reading with the transducer just below the surface and the signal strength (if so equipped)with the transducer aimed directly at the bottom. 2. Find a location on the hull to mount the transducer that complies with all of the following criteria: - As close to the centerline as possible - Where hull material is thinnest - Where the acoustic beam is clear of the keel - Where the transmission axis is perpendicular to the seabottom monitored at no heel angle). 3. Ensure the transducer will not be damaged by shifting objects or prepare to provide a protective cover. 4. Ensure the hull section to "shoot through" is not cored or delaminated. (If it is cored you can strip away the top substrate and core material to the outside hull surface for that small section of contact area required. You can test for delamination by tapping with a hammer). 5. Connect the electronics per instructions and apply power. 6. Mix a two part epoxy that will cure to a hardness similar to the transducer radiating surface. 7. Apply a fairly thin (1/8")layer of epoxy to the hull. (Ensure the epoxy is free from air bubbles). 8. Press the transducer firmly into the epoxy with a slight rocking motion to eliminate air bubbles and seat the transducer radiating surface in intimate contact with the hull. 9. Tape the transducer into place to prevent shifting during curing. 10. Observe the depthfinder readings and signal strength. Adjust the depth reading calibration (if so equipped)to match that measured beside the boat just below the surface to read actual water depth, else calibrate to read water depth below keel. If for any reason, the readings are erratic or the signal strength is substantially less (small loss to be expected) once the transducer is set in the epoxy as compared to the preliminary test, remove the transducer, wipe off the epoxy, and try a different spot.