I've never heard of one shooting through an aluminium hull. Lots of fibreglass boats have shoot-though hull transducers but I've never heard of one in an aluminium boat and from what I know, it's impossible. Ice has very different characteristics than metal. Some people drill a hole through large aluminium hulls and actually have the transducer on the bottom of the hull and the cable running through the hull.
Not sure how the magnet will work either as there isn't much metal in a transducer and the transducer needs to be at a specific angle to work properly.
Here's what Lowrance says about shot-thru-hull transducers.
Shoot-thru-hull transducers are epoxied directly to the inside of fiberglass boat hulls. The sound is transmitted and received through the hull of the boat - but at the cost of some loss of sonar performance. (You won't be able to "see" as deep with a shoot-thru-hull transducer as one that's mounted on the transom.) The hull has to be made of solid fiberglass. Don't attempt to shoot through aluminum, wood, or steel hulls. Sound can't pass through air, so if there's any wood, metal, or foam reinforcement, it must be removed from the inside of the hull before installing the transducer. Another disadvantage of the shoot-thru-hull transducer is it can't be adjusted for the best fish arches. Although there are disadvantages to a shoot-thru-hull transducer, the advantages are considerable. One, it can't be knocked off by a stump or rock since it's protected inside the hull. Two, since there is nothing protruding into the water flow, it generally works quite well at high speed if it is mounted where a clean laminar flow of water passes over the hull. Three, it can't be fouled by marine growth.
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