An outboard trolling marine motor assembly, conversion kit and method for converting a string trimmer into an outboard motor assembly. The assembly and kit featuring a propeller, a clamp assembly, a spacer and a mounting bracket. The propeller having a plurality of blades radially extending from a centrally located hub featuring a substantially centered non-circular recess. The propeller and spacer suitable for being mounted to a non-cylindrical prop-shaft. The clamp having a U-bolt with spaced apart threaded ends, fasteners and a block with a semi-circular slot and a plurality of apertures for receiving the ends of the U-bolt. Slot and U-bolt forming a substantially annular interior region. The mounting bracket having a pivotable body and at least one adjustable clamp for securing the motor assembly to a portion of a watercraft.