I don't have to much experience of narrowboat rudders but I have built wooden boats in the past. The rudder alignment is very important. Make sure the hull is as level as possible. Then hang a plumb Bob (weight attached to a bit of string) and it will show you how far out the rudder is. Adjust so it is perpendicular to the hull and there should be less vibration. Creating a rounded leading edge and tapered trailing edge might help as well. Also weed and build up of blacking won't help. Rudder rake fore and aft controls feel. A vertical rudder will be a light feel. Rake it aft for more if a weighted feel. Also the rudder position relative to the prop wash turbulence will affect things. Cheers
