I have a short shaft tiller on my 13' gheenoe that won't push this boat. I've tried every trim position on the motor. It won't open up. Every time I get up to speed the motor rev's and the prop loses bite. I had a 5hp that worked fine just needed a little more speed. I've been told it could be the hub or it could be the shaft is too short for the hull? Need some insight before I throw more money at it.