curved chines and transom edge

Discussion in 'Hydrodynamics and Aerodynamics' started by pistnbroke, Apr 7, 2011.

  1. pistnbroke
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    pistnbroke I try

    I have just been looking at a 12ft boat of conventional shape with 15 deg deadrise but the chine edges and underside to transom transition have a 30 mm radius curve....Now I always thought sharp edges was the correct construction for a planing boat . can anyoune let me know how they think this will affect performance ?
     
  2. PAR
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    PAR Yacht Designer/Builder

    Here we go again. There's another thread on going about this same subject.

    In a nut shell, you are correct in that a boat capable of planning, will like a crisp chine edge to separate flow and shed parasitic drag. This said, laying 'glass around a corner can be difficult so a radius is employed. 30 mm is a pretty big one, but not so unusual, depending on hull construction and material. Most production boats have a 6 to 12 mm radius.

    If you took two examples of this 12' boat, one with the round over chines and another with the forward portion of the chines rounded, but the aft half crisp, you wouldn't notice the difference in speed, except in moderate air. With the crisp chines aft, you'd be able to sustain plane in lighter winds, then the full length rounded over version (we're talking fractions of a knot here). In lighter winds, there'd be little difference (both would be in displacement mode) and in heavier winds there'd be little difference (both would be in plane mode). The difference would be measurable and would favor the crisp chine version when on plane, possably the rounded chine when off plane, but the amount of difference could easily be discounted to skipper skill or wind shifts, instead of hull form choices.
     
  3. pistnbroke
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    pistnbroke I try

    Not the same old thread its a Rotomoulded Polyethylene boat with may design anomolies and I dont understand why they have made such stupid mistakes .Its a power boat not a sail boat .This is only one "error " wait till you see the botom of the hull !!!
    This is the bottom tooking aft ..here are two longitudinal channels put in to stiffen the hull ..no problem but they dont come out at the transom ...they are 5 in deep and 4 in wide V shape.....about 18 in from the rear they blocked off by a 45 deg forward sloping part of the moulding ....this seems crazy to me for water flow on a boat capable of 25-30 kts....any view on this ??/
     

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  4. PAR
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    Well, powerboats in general usually can waste some HP to overcome shape inefficiencies. The radius and channels I understand as you do. It's possible they needed to reinforce the channel with some bridging. Underway this bridging would make for considerable drag, but not as much as you might think. The column of water trapped just forward of the angled bridge will act as a ramp to smooth the flow over it.
     
  5. pistnbroke
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    pistnbroke I try

    Crazy French ..what more can you say ......
     
  6. PAR
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    PAR Yacht Designer/Builder

    They can't fight either . . .
     
  7. PAR
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    PAR Yacht Designer/Builder

    Dear ,bjbhjb, which is how you signed you negative points award. Most of us are man enough to sign our points awards, apparently you aren't. In any case if you couldn't tell my last post was a tongue in cheek comment, an off color joke if you will, then you're going to have a difficult time in life. Buy some Revlon skin rejuvenator and grow yourself some hide bud . . .
     
  8. pistnbroke
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    pistnbroke I try

    I love the french NOW they banned the BURKA and they are fining people ..go the french
     
  9. PAR
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    PAR Yacht Designer/Builder

    Now, if they can only ban paints down around teenage boys butts . . .
     
  10. Jack Hickson
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    Jack Hickson New Member

    Kids , just say no to crack!
     
  11. PAR
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    PAR Yacht Designer/Builder


  12. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    arhh but you got to love those mini skirts held up with velcro clinging onto a 14 year olds brush......how do they do it at 16 when they shave it off ....???
     
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