Is this too much flam??

Discussion in 'Sailboats' started by mcm, Apr 18, 2017.

  1. bhnautika
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    bhnautika Senior Member

    Q1 all three
    Q2 Yes I am making some assumptions but light displacement boats tend to have flattish bottoms coupled with the flared sides would generally mean the CB would move out significantly making them stiff but you can get considerable rolling accelerations.
     
  2. mcm
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    mcm Senior Member

    @25deg angle of heel the designer calculated that the transverse shift of the center of buoyancy will only be 0.79'(0.24m). Hull bottom is 2'(0.61m) bellow the waterline creating a 21deg. dead rise angle to the waterline.

    Still, my main concern is whether that much (flare) in the top-side will kill the boats momentum as it heaves in a seaway.


    The designer is still making adjustments to the lines of the boat which is not yet named, and I don't have permission to reproduce the designer's work. As a consumer I am looking for second opinions before I spend too much money.
     
  3. bhnautika
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    bhnautika Senior Member

    It seems my assumptions about the mid section shape are wrong as more information comes to hand (21 degree dead rise). So is this close to the shape.
    I may be slow coming back.
     

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  4. Mr Efficiency
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    Mr Efficiency Senior Member

    So it is a new design with no examples in use ? Is there some reason to fixate on this boat in preference to existing, proven designs ?
     
  5. mcm
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    mcm Senior Member

    Thank's bhnautika, that's close, but I made a mistake.
    The dead rise angle from the bottom of the center-line to the waterline is 31deg. not 21deg.
    21Deg. is the dead rise angle from the bottom to 1' (0.3048m) bellow the waterline.
    And at 1' (0.3048m) below the waterline the the mid-ship beam is 5.13' (1.56m) overall or 2.57' (0.78m) from the center-line, while your mid-ship beam at 1' (0.3048m) below the waterline looks to be 4.55' (1.39m) overall, or 2.28' (0.69m) from the center-line.

    Yes, it's a new design, and my fixation is to be more involved in the process.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Maybe best to wait and see, rather than be the guinea pig.
     
  7. bhnautika
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    bhnautika Senior Member

    Mcm how about this shape. Heave can be influenced by more than just mid section shape , L/B ratio, L/disp, radius of gyration and wave spectrum. Then there is heave and stabilty. Top side flair may add resistance to heeled waterlines if they are to asymmetric, if you have concerns talk it over with the designer.
     

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  8. nzboy
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    nzboy Senior Member

    My take on this design is its very similar to racing designs of late 70s and 80s
    before canting keels and all the volvo stuff. You actually need a wide shear beam .As the boat heels the waterline beam increases and increases stability but draught decreases hence less resistance in theory
     
  9. mcm
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    mcm Senior Member

    So what you're saying is that; in your opinion, a wide shear beam won't stop the boat's momentum as it heaves, but rather, it's stability will increase as it heels and it's momentum might even increase with less resistance due to decreasing draft.

    I am not so sure. It's a double ended design so the lines won't change that much as it heels. The draft may decrease some, but the sectional drawings at 25deg heels doesn't show much if any decrease in wetted surface area at that angle of heel.

    I have the designer's opinion, but I want other opinions as to whether a narrower beam can create a more sea-kindly, motion comfort despite the light displacement.
    I want to avoid the structural exposure of a wide stern to breaking stern seas, as well as the pounding across wave crests of a wide dish speed-sled.
    And yet, hopefully with this light displacement, not get left too far behind.
     
  10. bhnautika
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    bhnautika Senior Member

    mcm as the hull is a double ender I am guessing its water plane area will be less so heave will less for its displacement. B/T (wl beam/draft) of 3.2 is ok for up wind also.
     
  11. nzboy
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    nzboy Senior Member

    Its fairly hard to comment on a design without seeing This link maybe of help
    http://sailingtrivia.ravenyachts.fr/2012/04/volvo-ocean-race-yacht-designs-by.html
     
  12. nzboy
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    nzboy Senior Member

    Francois_Chevalier-VOR2001-VOR2012.jpg These diagram shows evolution of designs
     
  13. nzboy
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    nzboy Senior Member

    chevalier - taglang, lines, maxi racing, naval architecture, sailing, volvo ocean race, yacht design, yacht lines, yachting If you copy these tags into google you
    will come up with the page in question as the address I posted wasnt specific enough
     
  14. CT249
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    CT249 Senior Member

    If the shape is like BHNautica's last sketch then it's similar to many existing boats that work well; the J/35, Davidson 42 are just two products of well respected designers that spring to mind.

    I've never been in a light boat that had its stern exposed to significant breaking wave impact. Maybe I've just been lucky but they tend to move quickly and don't create much of a fuss in the water that could "trip" a following sea.
     

  15. CT249
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    CT249 Senior Member

    Well, evolution of a sort. Arguably it's only positive evolution if your desire is for a monohull that is ever more complex and ever more expensive for its size and performance.
     
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