Skeg Repair/Reinforcement Design - aluminum sailboat

Discussion in 'Boat Design' started by poubj, Jan 27, 2023.

  1. poubj
    Joined: Dec 2009
    Posts: 4
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    Location: Hood River, OR

    poubj New Member

    Working on the design of a skeg repair on an aluminum sailboat.

    Cracks appeared on the welds between the skeg and the hull, and inside hull plate.

    This problem seems to be known for skegs that are simply welded to the bottom plate of the hull rather than being secured by a structural design: RUDDER SKEG REPAIR: Getting Ready for Spring - Wave Train (Charles Doane).

    The remedy is to fabricate a longer skeg that goes inside the hull and is held with transversal framing.

    The skeg as built is quite wide (when looking from the side), thus it has a relatively large area and is subject to large lateral forces when sailing. We are concerned that maybe, those large dynamic lateral forces, when sailing in rough seas, may be the cause of the failure.

    We see some hull designs where the skeg is much narrower (very high aspect ratio), and thus does not contribute significantly to the anti-drift plan. The function seems to be just to hold the rudder vertically, and little else.

    What are the pros and cons of having a wide (low aspect ratio) skeg like this? Versus a long a narrow skeg.

    Would it be worth making the new skeg slightly less wide to reduce the lateral forces applied to it?

  2. messabout
    Joined: Jan 2006
    Posts: 3,359
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    Location: Lakeland Fl USA

    messabout Senior Member

    The rudder appears to be bigger than the skeg. Forces on the rudder post play into the problem as much, or more than, the forces on the skeg. The rudder may also develop some vibrations in certain sea states or when maneuvering with the prop driving the boat.

    Look into the prospect of reinforcing the rudder post housing. Long term vibration, even small amplitude ones, eventually tend to work harden the aluminum, whereupon it becomes somewhat brittle.
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