I have a Hummingbird 535 Portable.  For some reason I just can't get the suction cup that holds the transducer to the boat to actually stick.  My boat is an aluminum jon boat.  Has anyone else had a similar problem?  Any suggestions on how to get it to stick better?

yeah i have the same one and it always comes off when i am moving or get in some weeds. I have found it stays on a little better if you get it wet first and try to get like half of the suction cup out of the water, it seems to work a little better. I've been thinking about making something more sturdy so it won't come off when i'm running. but i'm still thinking up ideas.

I was thinking it might be having problems because the aluminum boat is not completely smooth.  One option I thought might be to attach a flat piece of plastic to the transom.  However, before I go through all that I just wanted to see if anyone has a tip for making it stick better.  

try one of these

http://cabelas.com/cabelas/en/templates/links/link.jsp?id=0000844010095a&type=product&cmCat=search&returnPage=search-results1.jsp&No=20&noImage=0&Ntt=transducer&Ntk=Products&QueryText=transducer&Ntx=matchall&N=4887&Nty=1

A piece of plexiglass and some marine glue will do the trick!  I did this on my jonboat and my 10' bass hunter!

EXACTLY. Plexi Glass and Glue. You can make it any size or shape ya desire.

My buddy runs his like this. Stays put and still relativley light to handle.

I'll try that out...it defiantly should work.  Thanks guys!

Rather than pay $35 - $45 for a Cabela's bracket you can make your own fairly cheaply out of some scrap wood.  You could also bolt the transducer to the wood rather than messing with the suction cup.

I haven't had to do this but often think about how to build one  8-)