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New rudder for Zebedee

  • 22 Jan 2019 20:47
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    Reply # 7022183 on 6899643
    Anonymous

    Basically I glued on a  triangle of 4mm ply reinforced with 4 layers of glass.  There's a formula  that  says something like 30 % of chord as the max width.  It didn't end up quite as big as the plywood I had was smaller. I think it ended up 38 cm wide. The top plate was much smaller about 5 cm and went right around the trailing edge.  The hard part was getting the bottom plate exactly flat either the port or stbd side kept being higher ...looking at the article Arne recommended it shouldn't have been a triangle! 
  • 22 Jan 2019 03:42
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    Reply # 7014463 on 6899643
    Anonymous member

    Congratulations Alan for your performance in the Tall Ship Regatta.
    do you think the modifications you made to the rudder had something to do with it?
    what exactly are these transformations? my boat is in a yard at the moment and it would be a good opportunity to modify mine. I would be particularly interested in the size and profile of the plates.
    Bruno

    Last modified: 22 Jan 2019 08:44 | Anonymous member
  • 02 Dec 2018 02:17
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    Reply # 6941597 on 6899643
    Anonymous

    Excellent! I'll just copy them.   Many thanks! 
  • 01 Dec 2018 22:20
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    Reply # 6941436 on 6899643
    Anonymous member (Administrator)

    Here is how the endplate ended up looking like on a Freedom 30. The owner reported about big improvement. This is very close to how Phil Bolger designed them. I would just copy this, both at the lower end and for the 'cavitation plate', sitting about 10cm below the waterline.

    This isn't rocket science, it's just a question of forcing the the water flow aft in stead of letting it escape under the tip (and let air be sucked down at the surface).

    Arne
  • 01 Dec 2018 20:18
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    Reply # 6941272 on 6899643
    Anonymous

    What shape is best for the bottom and top plates?  I notice in the article,  that the bottom plate was in a delta shape. Should they extend aft beyond the rudder? 
  • 21 Nov 2018 01:26
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    Reply # 6918948 on 6899643
    Anonymous

    Excellent!  I've found the article. Many thanks! 
  • 20 Nov 2018 10:27
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    Reply # 6915459 on 6899643
    Anonymous member (Administrator)

    Alan,

    I suggest you look up JRA magazine 74, p.26. There, Karlis Kalnins describes how re rebuilt his rudder, almost identical to yours.

    Arne

    Last modified: 21 Nov 2018 08:46 | Anonymous member (Administrator)
  • 20 Nov 2018 03:15
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    Reply # 6915141 on 6899643
    Anonymous

    The chord at the top is 33 ins and at the bottom 31 ins. With 15% camber the difference between the two is 0.3 ins . 12 % of 33 is 3.96 and 15 % of 31 is 4.65 difference of. 7 ins. It might be easier to do the same shaping for both from the leading edge and just extend the flattish part just before the trailing edge at  the top. As you point out the difference is small . Would that still be as effective? 
  • 20 Nov 2018 02:01
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    Reply # 6915089 on 6899643
    Anonymous member

    Hi Alan,

    after seeing the rudder last Thursday I would suggest making the leading and trailing edges of the underwater section of the rudder vertical. This would add some area ahead of the pintle at the top and some extra area on the aft edge at the bottom. This could easily be done by adding a sheet of 18mm ply each side of the rudder with the overlaps trimmed on the center line to fit. Any additional shaping on the aft end could be done on the outside after it is all glued together. Half of a one and a half inch heavy wall PVC pipe would make a good leading edge to the rudder. It would need to be well roughed up before gluing in place and fiber glassing.

    All the best with the project, David.
  • 19 Nov 2018 20:18
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    Reply # 6914649 on 6899643
    Anonymous member (Administrator)

    Alan,

    what if you just keep the rudder's profile as it is and just give it a constant thickness? Then the thickness/chord will increase somewhat as you move downwards, but that may not do much harm. If you start with 12% thickness/chord at the upper end, how will it be at the lower end?

    Arne

    Last modified: 22 Nov 2018 09:38 | Anonymous member (Administrator)
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