Yup, Playdoh, or other such child's modelling clay.
Wanted to test fitting my transom mount
transducer inside the
hull and shooting through. Having read about creating a fluid filled wet well to put the
transducer in, I didn't want to go this
route until I had determined a clean location for best signal. With the idea being that the transducer needs "solid" contact all the through the
hull I took a lump of Playdoh and made a thick
bed to push the transducer into. The unit is a
raymarine WiFish BTW. Worked great, which surprised me. I need to pull the unit out and hang it over the side on a pole as a "gold standard" test for comparison, but in the meantime the Playdoh is good enough for testing purposes. Hope this helps, definately not intended as a long term
installation method!!