I have seen many people on here asking how to mount a transducer to an aluminum boat. Here is a guy who used two plungers to do do it.

http://katmasters.com/forum/viewtopic.php?f=244&t=17563

Pretty good idea. I plan on getting a FF real soon and don't really want to drill into my boat. Ill probably go the suction cup route but will save the plungers for home use.

That's nothing new.  The original Lowrance "green box" depth finders came with a very similar setup.

I think people worry a little too much about drilling on their boat. Suction cups will fail. Screws not so much. A little silicone around the screw and you'll be leak free, and have a cleaner install.

The only reason I could imagine using suction cups would be if you needed the unit to be portable.

I actually farbricated my own using left over aluminum strips from my mods, a deep 3" c-Clamp, and I bought a cheap bicycle tire tube.

It fits real good. I wrapped the whole thing in Rubber to keep it from scratching the crap out of the hull and hold it in place better. It has the benefit that I can remove it in about 5 minutes. I keep meaning to post some pics. It is ugly, but works well.

I bought some Marine Epoxy and glued the transducer mount to the boat and it seems to be fine. We'll see how long it lasts.

Jim