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You don't need 3" of pipe. Just as long as the business end of the transducer is wet and coupled to the hull you should get something. I don't have any experience with kevlar, but with my aluminum rowboat I just put the puck (this is long before my LX-7) in a puddle of water on the bottom of the boat. It worked fine, unless the water was contaminated with oil.
i used electricians putty. flatten out a piece onto the floor and press the ducer on top. just needs a thin layer to stick the ducer to the floor.
yea ..i don't want to goop my xducer..this is why i want to goop the piece of pvc to the hull..than drop the xducer into the pvc..with a bit of water.then i can take it out at the end of the day.
seems like this would obscure the sound waves being it's an insulator for energy. did you try other media's and this one worked best or is it what you had handy to try?check out the retail cost!http://www.amazon.com/Scotchfil-Electrical-Insulation-SCOTCHFIL-Length/dp/B001A5MBBU
i have tried the 3" PVC pipe sealed to the hull with water in it. seal did not stick. tried roughing the floor and siliconed the ducer to it and that did not stick. cleaning the silicone off the ducer was a buggar. went on a kayak site and saw this and tried it. sticks and stays in place. signal is accurate. temp is only a couple of degrees off. i compared my readings with a friend who had his directly in the water Cost of the putty is about $3. don't need much. http://www.homedepot.com/p/Gardner-Bender-Duct-Seal-Compound-1-lb-Plug-1-Each-DS-110/100212441