Boat transom design

Discussion in 'Powerboats' started by Kastally80, Jan 20, 2018.

  1. Kastally80
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    Kastally80 Chargui Yacht Design

    Hi ,
    Have you ever seen or designed boat transom like this one ? It's a 25' wakeboarding boat equipped with the new Volvo Peta FWD drive propulsion. Can anyone tell me please what are the pros and cons of this kind of transom ?
    I tried to make this tunnel as narrow as possible in order to not lose a lot of hydrodynamic lift.
    Thank u all Boat transom.jpg Boat transom.jpg Boat transom.jpg
     
  2. TANSL
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    TANSL Senior Member

    If you do not want to lose "hydrodynamic lift" the best thing you can do is eliminate this type of transom and make a more traditional, flat one. Perhaps you have some reason to place a transom of the type of the picture in which case only you can assess the pros and cons of each decision.
     
  3. Kastally80
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    Kastally80 Chargui Yacht Design

    We havent swim platform to protect the forward drive that's why we made this tunnel.
     
  4. TANSL
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    TANSL Senior Member

    Excuse me but I do not know what your forward drive is like and why it needs this special protection or why you need more hydrodynamic lift. How much hydrodynamic lift do you have with that configuration and how much would you need?
     
    Last edited: Jan 20, 2018
  5. Kastally80
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    Kastally80 Chargui Yacht Design

    FWD drive.jpg
    This is the Volvo FWD drive propulsion. It was made for wakeboarding and wakesurfing boats to get better wave.
    The swim platform protect the wakeboarder from the propeller and also protect the propulsion from the dock.
     
  6. TANSL
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    TANSL Senior Member

    The configuration that you want would seem appropriate, perhaps, in the case of an outboard but with the type of drive you are going to place, why can not you put a normal transom and a protective platform ?.
     
  7. Kastally80
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    Kastally80 Chargui Yacht Design

    The customer want a retractable platform
     
  8. Wayne Grabow
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    Wayne Grabow Senior Member

    I built a boat with a stern somewhat like this to provide more hydostatic buoyancy in support of a heavy outboard engine on a comparatively narrow stern. It works well and aesthetically helps hide the bulk of the engine.
     
  9. TANSL
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    TANSL Senior Member

    Wayne, you built a boat with a stern "somewhat like this" to get more hydrostatics buoyancy but the OP fears that stern will diminish the "hydrodynamic lift". It seems that one of you is not right.
    On the other hand, if you place a normal transom in the extreme part of the stern, you will get much more buoyancyt than if you put that "hole" in the stern.
    On the other hand the drive that the OP proposes does not seem to be an outboard.
     
  10. DCockey
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    DCockey Senior Member

    The longitudinal location of the center of gravity may be as important or perhaps more important to the performance of the boat than the difference in "hydrodynamic lift". The notch appears to shift the CG forward if everything else stays the same.

    Kastally80, Do you have specific concerns about the amount of hydrodynamic lift? My understanding is wakeboarding boats usually need a heavy bottom loading (ratio boat weight to planing surface area) in order to generate sufficient size waves. Have you compared this ratio for your design to successful wakeboarding boats of a similar size.
     
  11. TANSL
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    TANSL Senior Member

    Everything does not stay the same because the CoB moves forward more than the CoG.
     
  12. fallguy
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    fallguy Senior Member

    Forgive me, I am NOT qualified to answer, but curious.

    IF you shorten the distance from the bow to the transom or if you do the reverse image; perhaps this would help understand the effects.

    More simply, a bolt on bracket would be the reverse and the other extreme would be propulsion from the bow with the vee removed.

    This is a management method to go to extremes for perspective.

    Many of the posters here understand the effects of the extremes far better than do I, but the vee provides directional stability in turns for one example, so no vee or less vee would result in slip, for one?

    Kind regards.
     
  13. Kastally80
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    Kastally80 Chargui Yacht Design

    Thank u every one for your help
    Maybe the right question i had to ask was : what kind of wake can generate this transom compared to normal flat one ? will it generate more drag due to shape and lack of lift ?
     
  14. TANSL
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    TANSL Senior Member

    Of course, a much more irregular wake than that of a flat transom.
    It will generate more much drag but not due by the lack of lift but just for the shape. The more regular the bottom, the more regular the wake will be.
     

  15. Kastally80
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    Kastally80 Chargui Yacht Design

    Do you think that this additional drag can improve wave shape ?
     
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