Basic electrical help needed? Answered

Hello everyone i'll try to keep this short and sweet. In my next project I will be re-Building a trolling motor. The trolling motor runs on a 12 volt battery, and draws between 5 to 30 amps. The problem I have is that the control unit/head of the trolling motor is destroyed. In other words all i have at this point is a 12 volt motor connected directly to a 12 volt battery. The trolling motor is very powerful and I don't want to run it full power all the time. This made me look for a 30 amp dimmer switch, just like the ones people have in their homes. With no results I don't know what to do. I am thinking about using a 600 watt AC dimmer switch like the ones in peoples homes, but I don't know if it will work with a DC circut like the one I have. Thanks for your time and help.  ~KayakKid