It only needs one. The transducer saver web site shows it. You also need the big hose clamps. They work great and that's a great price And owns zip tie to hold the cable against the shield
I don't know which mount model you were looking at, but the one sold uses two hose clamps. Look at the photo and you can see TWO hose clamp slots - one at each end of the mount. It certainly would not work with a single hose clamp (as you advise) at one end. Also the size hose clamp needed (you said "big") is determined by the motor it will be mounted on, and not the mount itself. I wonder how you knew which trolling motor the person asking the question would be using?