I have a 20' Grady-White that I use in Calif. delta slow trolling for striper & salmon. I had a 20hp merc for trolling but the theives got to it. I keep the boat at my dock, which I can't see from the house. I want a small motor which is light enough to hang over the stern and attach to bracket. I have been using an old 9.5 johnson, but it is a little hard on the back. How small of a motor can I get that will push this boat at a slow troll? I see some of the 3 & 4 hp that look very light, but I don't know if they would push me.