rudder shape

  • May 10, 2012 5:05 AM
    Message # 916408

    my w28 rudder seems to be somewhat misshapped.  it is convex on one side and concave on the other.  when viewed from astern it seems to have a twist.  in profile, starting from just below the lower pintle the aft edge curves upwards on a radius up to a point at a step just above the water line.  the trailing edge is squared off at the top and rounded at the bottom. there is some evidence that it has been repaired or strengthened. when the tiller is amidships a sighting along the port face of the rudder leads to a point about 18"  to the port side of the cutwater at the bow.  the surface is rather rough and definately not fair. if i could work out how to attach a picture that would tell you some of the story.

    in the construction manual, there is a partly dimensioned profile shape for a rudder for "nigella" and "windfall". this profile shows a rudder with a straight lower edge nearly parallel to the waterline and and aft edge in a straight line up to the step.

    i made a full scale plywood template of this rudder and compared it to mine.  they are roughly the same area, but due to its curvature, my rudder is short on area at the bottom and long on area at the top.

    i had a discussion with the local shipwright today and he suggests that in
    view of the severe twist and warping of the surfaces that perhaps the best
    way to approach a repair would be to cut away all but about the foreward
    foot or so of the rudder,  glue on some new foam and then shape and
    fiberglass a new aft portion to match the outline shape of the rudder shown
    in the construction manual:

    so i have a few questions:

    is cutting away that much likely to interfere with some hidden internal
    structural component of the rudder?

    did the rudder shapes shown in the construction manual produce good steering

    would it be okay to streamline the rudder to produce a bit more hydrodynamic
    cross section with a much thinner trailing edge?  my trailing edge is about
    2" wide.

    has anybody built a new one?

    i would be grateful for any comments.