Dalslandia

If you do 6 mph now with 40 hp you will do 6,67 mph with 55 HP Jan

I know this is an old thread, but still interesting. Trilby Tim, As they said in the commercial, "I am not just a dentist I am a mother too" I am not just a canal boat Skipper, I am also a airplane propeller designer, www.jcpropellerdesign.com (and a father too) and have also studied ducted propellers (Kort) and shrouded propellers a little. I designed a Shilling rudder of my own design, for my canal boat. www.dalslandia.com onboard her I have passed 50-60.000 locks. When reading about your vibrations from propeller, I can think of 2 reasons in relation to the Kitchen rudder. At forward drive with some amount of power, the propeller sucks in (induce) a lot more water then the forward speed, you say you have about 35% slip. if we consider the slowed down water at the rear of the keel we can think it is even higher, maybe 50% When accelerating probably 100% this mean the propeller suck in water into the duct or shroud shaped rudder with a lot of force and speed, so the water isn't coming from just straight a head of the duct but also from the side like a trumpet shaped funnel. at low speed the water even come from behind of the leading edge lip, So the water is going around this lip at a high velocity so it can't follow the inner side of the entrance if it is to sharp, (think centrifugal force here) So it need a big radius lip for the water to stay attached and not going turbulent, a good lip here will also give extra thrust. The other reason I can think of is the shape of the hull just forward of the propeller, yours look somewhat blunt, it rise 2 questions can the water follow the sides? and at what angle is the water going into the duct and propeller? Will a propeller with more rake be better? Jan