Chine at bow

Discussion in 'Sailboats' started by frank smith, Oct 23, 2009.

  1. frank smith
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    frank smith Senior Member

    I notice that there has been a lowering of the chine at the bow on sailboats over the years. In the past there was much effort into fairing the chine into the bow a smoothly as possible . but chine designs that I see today seem to have a rather straight level chine from midships forward .
    How is this an improvement ?

    Frank
     
  2. gonzo
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    gonzo Senior Member

    There aren't really many new modern designs with hard chines. Some designers that cater to DIY still work on them, but they are rare.
     
  3. Paul B

    Paul B Previous Member

    You need to get out more.

    Many modern designs, especially ones aimed at fast reaching and running, have chines.

    Everything from I14 dinghys, to Sportboats from 5.5 meters to 9 meters and more, to fast IRC boats in the 40 to 45 foot range, the TP52 fleet, the Volvo 70 fleet, the Mini Maxi fleet, and even the latest 100 foot canting keel weapon (pic attached).

    Your location says you are in London. Pick up a copy of Seahorse magazine from a local magazine stand and flip through it.
     

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  4. frank smith
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    frank smith Senior Member

    because of the inherent qualities of damping and construction I am thinking of chine hulls made from sheet material . Thus the question of chine action at the bow.
    Frank
     
  5. gonzo
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    gonzo Senior Member

    I understood it is a question of hard chine hulls with rather flat panels.
     
  6. apex1

    apex1 Guest

    Hmm, and when you would tell me where you see any chine at the bow of the boat shown? (above waterline of course)

    Can we see that when going out more?:D
     
  7. Paul B

    Paul B Previous Member

    I'm not the one who made the claim that chines seem to be running all the way to the bow more often in modern designs, am I?

    Some do, like the Humphries Volvo 70 design, others do not. The photo of Speedboat was handy to illustrate the use of a chine on a modern design.
     
  8. apex1

    apex1 Guest

    Nono, you did´nt, but that was the issue, was´nt it?
     
  9. Paul B

    Paul B Previous Member

    No, that wasn't the point I was taking issue with. There was a claim that "There aren't really many new modern designs with hard chines."

    The fact is, there are.

    For example, this sportboat design by Paul Bieker is currently in build in Houston, Tx.
     

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  10. frank smith
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    frank smith Senior Member

    That is a nice boat with a nice chine . Dose that help with separation?
    But that is still not what I am getting at

    Yes, flat panels . It could be multi chine or single chine . What would be the best way to shape it so as to have the best effect on water flow.

    In days of old the ides was to have the chine disappear after it left the water.
    think in terms of an origami design . Now it is the current fashion to leave the chine in the water , more or less parallel to the water line .
     
  11. Guest625101138

    Guest625101138 Previous Member

    Frank
    If you look at the waterlines on a hull with an immersed chine the angle of flow around the chine is not very severe. Once you bring in the boundary layer it is softened further. The water does not mind if it is making a slight turn or following a very gentle curve.

    An immersed hard chine can improve the block coefficient so you get more displacement for the beam and this will reduce wave drag for any given displacement.

    Then there is the benefit you get from the better planing ability of a flatter surface. Works better reaching and going downwind than a rounded section.

    The more severe immersed hard chine also provides a cushioning deep "V" when heeled going to windward.

    Post #71 on this thread is a good example:
    http://www.boatdesign.net/forums/sa...-sides-flat-deck-flat-everything-26770-5.html
    A boat like this is simple to build and will perform very well. You see the trend to length and slenderness as this equates to easily driven. Curves are harder to make and add no performance advantage.

    At displacement speed there is very little advantage to a round section hull over a rectangular section hull - of the order of 1 to 2%. At speed the flat sections will provide lift much earlier so the boat will get up and go faster.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    "..An immersed hard chine can improve the block coefficient so you get more displacement for the beam and this will reduce wave drag..."

    er.....so let me get this right. More displacement for the same length, ie decreasing L/D ratio improves the residuary!!!

    Wrong.
    Increasing the L/D ratio decreases the residuary.

    "..At displacement speed there is very little advantage to a round section hull over a rectangular section hull - of the order of 1 to 2%..."

    At low Fn's a bilge with a hard chine can add as much as 10% to the total resistance compared to a soft round bilge. But of course does depends on the size of the radius and the Fn.

    A hard chine is ostensibly only for 1) higher Fn's or 2) ease of construction hulls. There are other minor benefits, as noted for yachts - if at 'ideal conditions' when reaching (since the chine is still underwater and creating drag, but now offset by some minor lift), but these are not the principal reason for going hard chine or not.
     
  13. gonzo
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    gonzo Senior Member

    Some old chine designs, like the Sea Bird, would plane at over 12 kts. The chine is hard almost to the bowstem .
     
  14. frank smith
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    frank smith Senior Member

    Heeled over the flat bow panel would provide a lot of lift . It is also a LDB ,
    so the chine may help to control water .

    Ben Seaborn , the designer of the Thunderbird 26 said that he used paper to rap around an existing hull model to see how it might work . Ther have been versions scaled up to 32' that worked well .

    But the question remains . How would it be done today ? would you pull the water line out and lower the chine.
     

  15. gonzo
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    gonzo Senior Member

    I think that all the successful hulls have the chine above the waterline. Some, like Frer's Supercadete, had a chine in the center which faded fore and aft.
     
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