stepped hull bottoms

Discussion in 'Fiberglass and Composite Boat Building' started by brokensheer, Mar 9, 2011.

  1. brokensheer
    Joined: Jun 2009
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    Location: So. Md

    brokensheer Senior Member

    I was looking at some high perf. style boats and wondering at what speed to steppped hull come to life, I understand the step has to do with breaking surface tension , will they be of a benifit on a modern sportfishing hull , ?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The hull has to be designed for the steps and yes they break surface tension, but mostly are designed to separate flow from the hull at higher speeds. A sportfishing boat is a function of the craft's use, not the hull shape, which would likely be a monohedron, with progressive step(s) buttock angles if it was a stepped hull.
     
  3. jiggerpro
    Joined: Sep 2007
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    Location: spain

    jiggerpro Senior Member

    This has been discussed several times, in this and other forums, in fact in another one, one of the contributors who work for a renowned brand said something amazing they modified a hull mould to incorporate steps and the same boat with and without the steps did not show any change in performace.

    On the other hand, I have always wondered why the effect of the steps shopuld be so different from the effect of redans ( or lifting strakes) since IMHO, both cause turbulence in the top layer of water and cause bubbles underneath.

    Many owners claim that their boats do certainly behave like having less drag even at slow speeds should be believed ??
     
  4. brokensheer
    Joined: Jun 2009
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    Location: So. Md

    brokensheer Senior Member

    Wow I would not have thought there would be an effect at low speed
     
  5. jiggerpro
    Joined: Sep 2007
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    Location: spain

    jiggerpro Senior Member

    It seems people are not very collaborative here ...............
     
  6. anthony goodson
    Joined: Mar 2007
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    Location: Dorset UK & Murcia Spain

    anthony goodson Senior Member

    There is being collaborative ,and there is repetition.
     

  7. Kestrel
    Joined: Nov 2010
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    Location: Milan Italy

    Kestrel Junior Member

    Hi,
    It should be specified if we are talking about tranverse step or not, if we mean hull bottom tranverse steps (often mentioned as "redans"), there are many threads in the forum, one is here:
    http://www.boatdesign.net/forums/boat-design/stepped-hull-resistance-35492.html
    You can give a look and get some ideas.
    We made some experiences on (redan) stepped hulls, not for racing or top performance, but for best behaviour at cruise speed, in transition from displacement to planing conditions, high carried loads and rough waters. The results were very good if every parameter (trims, deadrise, step position and height, lifting surface aspect-ratio, wake effect on afterbody surface,...) were calculated and accurately selected to be the optmum mix. The best efficiency was found with single step design.
    We think there are many rooms still to explore with this solution, even if it's 100 years old, and many valid examples come from the past.
    Regards
     
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