i dont think you can get one to work with an aluminum hull.
I have been looking around about that, there are mixed reviews. I am not worried about detail, I just want to see the bottom and how deep it is. Also looking at something called a Alumaducer, made just for this application. Also found that if hull is less than .015 thick not to much is lost. Also found out if you mount in the bilge with enough water to submerge at least half of it, it will shoot right through. There is another transducer I have owned in the past also the was a 1/4-3/8" thick and mounted flush to the bottom facing, outside rear of the hull and that worked good too.