TP is right, we need more information to try to help you. In addition to the info TP asked about, what have you spent the $100s on to "fix" the problem? Are you using a teflon liner inside the brass stuffing tube? Do you have a photo of the damaged cable? Does the boat run at all, or does the cable fail immediately?
Also is the wind in the cable rotating in the proper direction. You will unravle it if the cable is spinning backward. What size cable are you using. You should be using a minimum .150 cable. .187 if you have a heavy torque load. What about thrust bearings? Are you running one on the motor shaft to unload there also? Like the other guys mentioned we need more info .