tearing your boat up going up those riffles sounds about right, I saw a boat try and go up, started hitting gravel with the old prop, he shut her down and let his buddy try the trolling moter, it wouldnt hold so they headed back down the riffle, sounded like they hit those underwater logs, probably put a little dent in the side of their boat. Guess you better have a jet to be tryin that stuff, oh by the way we probably caught 100 whites up above the riffle.