Looking to buy a new bow-mount trolling motor. I have an 89' spectrum 17 1/2' deep V aluminum boat with the dual console/walkthru. I was checking into buying the Minn Kota Powerdrive 40lb thrust and 48" shaft. I know that a 50+lbs and 50"+ shaft would be better, but is it really necessary with this size boat. The boat currently has an old Mercrury Thruster on it the says "RL21", which I think is only a model # and not thrust size. This motor does not run and is probably not worth fixing and if measured correctly, appears to have a 42" shaft. I would mainly be fishing inland lakes and occasionally Lk. St. Clair and Saginaw Bay.