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Re: Rudder Placement (hyrdrodynamic Q.)
By:Randy Knauff
Date: 6/21/1999, 10:00 pm
In Response To: Rudder Placement (hyrdrodynamic Q.) (David Walker)

> I am mounting a small trim tab to the rear of my yak to compensate for a
> minor tendency to steer to port. It will be attached to boat with a
> friction hinge so as to basically be fixed in place at a set angle but
> also to allow for adjustments as needed. Anyway, because the rear of my
> kayak is angled (i.e., if looking at it from the side....I may not be
> saying this clearly but the stem does not rise perpendicularly from the
> water but angles backwards somewhat as many kayaks do) and because hinge
> would attach to the trim tab a little bit behind the most forward part of
> the trim tab (because the lower part of the trim tab projects forward to
> follow stem line), angling trim tab to right would send the part of the
> trim tab which is behind hinge to the right and would send the smaller
> part of trim tab which ends up being in front of hinge joint to the left
> of the stem. Both the front and the back should still be pushing boat in
> the direction I want it to go but I am just wondering if there are any
> consequences of this which I should be aware of. I believe this issue may
> be called something like balanced vs unbalanced rudder design in nautical
> engineering (but I may be mistaken).

> This is not easy for me to explain on "paper" but if anyone
> understands what I'm saying and has any comments, great.

> Thanks, Dave Hi Dave, Not sure if I understand, but if it is similar to a balanced elevator on an airplane tail... The small part that sticks out opposite the main deflecting portion of the control is directly in the flow of oncoming air (water?). That little pressure helps hold the elevator deflected without so much mechanical or manual exertion by the pilot on the controls in the cockpit.

The larger deflected portion of the elevator (say it is down) lifts the tail to lower the nose of the plane. The small section sticking out the other way in the wind stream helps hold the large section down BUT it does catch some wind which pushes the tail DOWN (counteractive) and it creates DRAG. But both are small forces relative to the large force of the big portion of the elevator and are acceptable losses to the plane designer.

Whether the drag and reverse pressure is acceptable on a kayak trim tab is probably less certain. It may be easier to correct for the turn with the way you load the kayak or putting it a bit on edge to be continually carving just a little.

Randy

Messages In This Thread

Rudder Placement (hyrdrodynamic Q.)
David Walker -- 6/19/1999, 4:20 pm
Re: Rudder Placement (hyrdrodynamic Q.)
Randy Knauff -- 6/21/1999, 10:00 pm