Inside mounting for depth transducer in Al hull

[Epicurean]

I'd like to have a spare depth sounder (for spare depth?). But I don't want to put another hole in my boat. So, I'd like to mount it inside. I have an aluminium boat. I've never seen it mentioned whether or not it works inside a metal hull. Does anyone have experience doing this? I would think the sound propagation properties of metal are so great that it would. But am I missing something?

[GordMay]

The properties of solid (uncored) GRP, with regard to ultrasonic waves, are similar to that of water.
Airmar specifies their in-hull transducers for "Solid Fiberglass" hulls, but add, "Call for Aluminum hull applications".
This suggests they may make "special" shoot-through tranducers for aluminum hulls.

[Epicurean]

Thanks. I guess an Airmar call is in order.