I found this out during my last trip.
I was setting the TM down into the water and noticed the (transducer) cable had come loose of the rigging. Not thinking, I continued. POP! 797c2i head unit overboard. Ugh. My heart dropped into my rectum (what a feeling that is...) when I heard several hits on the bottom of the hull. The sounds were moving aft; I followed. From the transom pops the head unit! I was shocked, to say the least. I snatched it up and put it back in the mount. It still worked. WOW!
I had no idea that the head unit would float. For the record - NOT going to try this with the 997...!