J,

I ask the same question to my trolling motor repair man. He said it would not hurt them and that it would probably last longer since the motor was designed to run on a higher voltage. I think that as long as your wanting to run a higher rated voltage motor on lower voltage, then you shouldn't harm it at all.

Think about it! If you run a motor long enough to drain the battery down, are you not running it on a lower voltage. Then after you recharge the battery, the motor runs find without any damage.

Just a thought!