Reply To: Screw Lifting Frames

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Frank Scott

    The Transactions of the Institution of Naval Architects are a valuable research source that show contemporary thinking on such subjects.
    I very much doubt that it was all worth it. The weight & cost would have been significant, and when the lifting frame was raised the ‘screw aperture’ (now minus actual screw) would have been larger than before & the resultant increase in cross flow would have had an adverse impact on rudder performance.
    Modern sail training ship designers who have fitted single screw have had to pay careful attention to rudder design because of the screw aperture problem.