Mike, you can use the stock transducer that comes with the unit on the ice with a little ingenuity. However, the ice transducer makes things so much easier..
http://store.humminbird.com/products/314001?product_id=56705ccd03fc815f9a883ebcb7c064a7
I've got a 788CI that I will be using this year in my portable pack (Used a 747C before that, worked great!)