Why does multihulls have pointy bows?

Discussion in 'Multihulls' started by bjn, Jan 22, 2017.

  1. pogo
    Joined: Mar 2010
    Posts: 338
    Likes: 8, Points: 18, Legacy Rep: 73
    Location: Germany Northsea

    pogo ingenious dilletante

    I don't agree w. you.
    The first frames are above WL always V-shaped. Together with the " modern" vertikal stem ( for a longer WL) this results in a bigger radius at deck level.
    Simple 3d geometrie.
    Please compare with older yachts with forward raked stem, whole stem has one radius.
    http://www.google.de/search?sclient.......0...1.1.64.tablet-gws..14.0.0.Kk0OC9cUA7k

    Why do mono - and multihulls with vertical stems , x - bows , inverse bows have no bigger radius at deck level ?
    Tumblehome hulls , at least the first frames !

    http://www.google.de/search?sclient.......0...1.1.64.tablet-gws..14.0.0.Kk0OC9cUA7k

    See also the latest " Hugo Boss" and wave-piercers.


    What do we learn ?
    There is a trend towards sharp stems.
    Together with the set back masts the seemingly more little volumed sharp bowsections they have a long enough leverage arm to compensate negative trim-angles ( bow bourying ). " Seemingly" , ' cause the volume is hidden in the length.
    Those bowsections don' t loose as much speed as a conventional v- shaped bow section when buried.
    The v- shaped bow sections answers to a negative trim- angle with progressive increase of volume , of static lift --for the cost of speed - thus more torque for pitchpoling---a brake.
    These bows can be seen as " non- sharp bows " .
    When waterline comes to deck level , the now negative angled deck ( (flat deck ! ) generates negative lift. one can imagine what happens --see Hobie 16. Brutal pitchpoling.

    The other world, the very long tumblehome bow sections , very sharp, nearly wave pearcers. The most drastic boats are " Sodebo" and her sistership "IDEC" , irens design.
    Even Under negative trim-angle these boats are going " thru".

    .....and IDEC spoke to the ocean:
    " Me, I am the sharp , hot knife, you are the butter ."

    There is a famous vid of Sodebo nearly pitchpoling after her start to single handed rw record attempt.
    Can somebody post it please ?


    Note that these radical racer solutions are not for cruising boats . They are impractical , you have a much longer and very narrow bow without a deck.

    But, the trend for bows is : be sharp and long.




    pogo



    P.S
    "Sharp" .
    I 've an old Joe Jackson LP , 1979 british New Wave --- "Look sharp" . I gonna hear it now.
     

  2. UpOnStands
    Joined: Nov 2015
    Posts: 574
    Likes: 5, Points: 18, Legacy Rep: 16
    Location: Sydney

    UpOnStands Senior Member

    sorry but you failed to read the thread carefully. OP wanted to know why stems were not deliberately designed to prevent separation/drag, i.e. why aren't they rounded rather than sharp.
    Your #1 is contradicted by your #2. Simply, if the designer wants a traditional style bow he uses V frames otherwise not. OP has extensive sailing experience so the rest 3/4/5/6 are true but not answering the OP's question.
     
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