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Rudder Alignment  Bottom

  • I seem to remember some discussion a while back on rudder alignment and wanting to have a slight toe-in on the leading edge something to do with Ackerman thingies... but this was for asymmetrical hulls...

    Anyone know if this holds true for boarded (center or dagger) boats?

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    John Schwartz
    Ventura, CA
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  • Straight to slight toe-in (never toe out). Check the assembly manual from the manufacture. They usually always give this.
  • Toe in and ackerman are two separate issues.

    Toe in is desireable because when we sail upwind, we pull the tiller slightly to windward to generate lift out of the leeward (burdened) rudder. A slight toe in allows the leeward rudder to have a slight angle of attack while the windward rudder has a zero angle of attack, so less drag.

    Ackerman has to do with the angle of the tiller arms not being parallel to the centerline of the boat. The tiller arms being turned inboard, through some tricky geometry, allows the inner rudder to turn at a tighter angle than the outer rudder to account for the difference in turn radius of the two hulls as the boat turns.

    sm
  • Ackerman geometry in a rudder system involves the entire system. The extensions from the casting are angled at a specific point toward the cat's centerline and a shorter crossbar is used. Going straight, the standard 2mm toe-in is common, but altering an P 18-2 rudder system to Ackerman geometry will involve significant math to figure out how much to bend the tubes from the castings to get the optimal turning radius. As an example, the Dart 18 has Ackerman geometry in it's rudder system. At least one of the NACRAs does as well.

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    Sheet In!
    Bob
    ___/)_____/)_/)____/)____/)_____/)/)__________/)__
    Prindle 18-2 #244 "Wakizashi"
    Prindle 16 #3690 "Pegasus" Sold (sigh)
    AZ Multihull Fleet 42 member
    (Way) Past Commodore of Prindle Fleet 14
    Arizona, USA
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  • klozhaldAckerman geometry in a rudder system involves the entire system. The extensions from the casting are angled at a specific point toward the cat's centerline and a shorter crossbar is used. Going straight, the standard 2mm toe-in is common, but altering an P 18-2 rudder system to Ackerman geometry will involve significant math to figure out how much to bend the tubes from the castings to get the optimal turning radius. As an example, the Dart 18 has Ackerman geometry in it's rudder system. At least one of the NACRAs does as well.


    Thanks Bob... 2 mm... we're talking 5/64" my tape rule only goes to 1/16"... that's good enough for guberment work... icon_lol

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    John Schwartz
    Ventura, CA
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