Oh...well, what you want is slow cure 2 part epoxy then. Build a dam around the transducer out of playdoh or plumbers wax, mix the epoxy sloooowwwwwllllllyyyyyy. You want absolutely no bubbles in the mix, pour in about 1/2 to 2/3 up the side of the ducerand let cure to directions.

Now, having said that.....it is possible with a regular transducer to shoot through aluminum, but results vary and some just can't get it to work at all. There is a ducer specifically designed for shooting through aluminum by some company other than H'bird or Lowrance, but it's high dollar.

Personally, I wouldn't try it, but it may work out for ya. You can test it by building that dam, filling it with water and placing something on top of the ducer to hold as flush as possible and easing around. If it works that way, you've got a 50/50 shot of it working with the epoxy on aluminum. Catch is, if it doesn't, you've got a 70/30 shot of ruining the tranducer when you try and remove from the epoxy installation.

Wannabe....