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Old 06-19-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Re:Brent's comment on the outboard rudder

I would disagree with you Brent. In my experience in designing boats with outboard rudders they operate in the turbulent flow of the transom when the transom drags at higher speeds and this can make the outboard rudder more prone to ventilating more rather than less. If I wanted a rudder that would not be prone to ventilating I would tuck it well under the counter so the root was immersed at all speeds.

When I designed the replacement outboard rudder for the 73' ATALANTA I was quite surprised at the amount of turbulence at the surface. In fact, in retrospect I should have continued the rudder foil up higher onto the transom to help reduce this. You see this rudder placement on almost all high performance boats today, rudder tucked under the counter. Although there are certainly benefits of hanging the rudder off the transom on smaller boats where you want the rudder as far aft as possible. But you also see the same, high performance smaller boats going to twin rudders so the leeward rudder is well immersed at speed when the boat is heeled.

Originally ATALANTA, a Bill Tripp Sr. design, had two rudders. One was forward attached to the keel. The other was a hinge up rudder hung on the transom intended to be used for downwind sailing when the forward rudder was not effective. Over time the owner realized the outboard rudder gave better conrtrol all the time and with the IOR penalty for movable appendages also impacting the situation the forward rudder was welded in place. The outboard rudder was welded permanently in the lowered position. All steering was then done by the outboard rudder. But being a hinged rudder (like on a Hobie cat but much bigger) the outboard rudder lacked some finesse in the transitional area to the upper cheeks. My replacement rudder had better foils and was one piece and a more elegant and lower drag design.
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Last edited by bobperry; 06-19-2013 at 04:25 PM.
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