Twin Rudder lead and sizing?

Discussion in 'Hydrodynamics and Aerodynamics' started by Claudio Valerio Parboni, Jun 8, 2021.

  1. Claudio Valerio Parboni
    Joined: Jul 2018
    Posts: 16
    Likes: 0, Points: 1
    Location: Roma

    Claudio Valerio Parboni Junior Member

    Dear All,

    I am currently facing the task of sizing a twin rudder system for a sailing yacht.
    My current method has been to heel the boat at an expected heel angle (IE 20°) and establish an ideal value for lead, then size rudder area (projected on the heeled plane) based on said lead.

    I am using the Nomoto method: (Extend the keel to the DWL to account for hull contribution, use a rudder reduction factor of 0.4 and take the individual CLRs about the foil's quarter chord line). This is mentioned both in Principles of Yacht Design and Fabio Fossati's Aero-Hydrodynamics book.

    I am not entirely sure on this method since in these books it only mentions single rudder systems, I also immagine that a rudder which is offset to leward will produce a "bear-away" moment, thanks to its own drag and I am not sure how much it contributes to lead calculation (probably very little).

    I have searched a bit on the past few days but I could not find much on papers nor on this forum.
    wanted to hear your thoughts.

    Hopefully I am just overthinking over a simple issue.

    Cheers,

    Claudio
     
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