Bolt-On Chine

Discussion in 'Sailboats' started by SuperPiper, Sep 23, 2021.

  1. SuperPiper
    Joined: Jan 2003
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    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    All the recent fast boats have chines. But, my old girl has a round bottom.

    Is it feasible to bolt a spray rail to the hull (above the DWL) to trip the flow as the boat begins to heel, or starts to generate a quarter wave?
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    It would probably help if you identified the boat
     
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  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    SuperPiper, are you referring to your 'radically modified' Sandpiper 565?
    (I had a look at your profile notes, and there is a choice of the Sandpiper, a 10' dinghy, and a J 35).

    Here is some reference info on her for other readers -
    https://sailboatdata.com/sailboat/sandpiper-565

    I really don't think that bolting on appendages to your hull is going to improve matters - you might even make things worse overall.
     
  4. HJS
    Joined: Nov 2008
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    HJS Member

    The purpose of the chine is mainly to place displacement where it is useful to increase stability.
    JS
     

    Attached Files:

  5. SuperPiper
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    SuperPiper Men With Little Boats . .

    HJS, sweet ride! What is it? Your design? Your build? Is she as quick as she looks?

    Yes, the original post was made with the 'Piper in mind. But, I'm sure the answer could be applied to any round-bottomed boat.

    So what exactly does the chine accomplish? Is it just to move the displacement outboard? Or, is there a hydrodynamic benefit of having a sharp edge along the quarter?
     
  6. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Chines are frequently used to provide for clean separation of the water from the bottom while planing.
     
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  7. CT249
    Joined: May 2003
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    CT249 Senior Member

    Depends on the boat and intended purpose, as D Cockey notes. In most Australian performance dinghies and skiffs, for example, the chine is mainly to prevent water wrapping around the bilge, and therefore increasing wetted surface.
     
  8. SuperPiper
    Joined: Jan 2003
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    SuperPiper Men With Little Boats . .

    Yeah, that's my understanding too. Hydrodynamics For Dummies suggests that allowing the wave to cling to the trailing rocker provides some suction and pulls the transom down, causing the boat to squat. Tripping or ventilating the flow would let the hull pop free. Yes? No? Have I got that all wrong?
     
  9. Steve Clark
    Joined: Jul 2004
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    Location: Narragansett Bay RI

    Steve Clark Charged Particle

    Chines are given credit for all sorts of benefits, few of which are attributable to the chine itself.
    When you build with sheet goods, plywood or foam, you have to go to some trouble to avoid having sharp corners.
    As these are useful light materials for boat building, many fast light boats have chines because it’s the easy way to build.
    Otherwise, many boats have chines because there are measurement points. The International 14, for example, has measurement point to enforce a minimum waterline beam. This is just above the load waterline, and so almost all boats have a sharp change in section curvature (is a chine) exactly at that point.
    Many modern cruising boats have a chine aft to permit a larger bunk in the owners cabin.
    Spray drag increases with speed, and you have to stop it from sticking to the hull. Testing showed that this becomes a dominant source of drag at about 20 knots. Which explains spray rails on motorboats and seaplane floats, and why most fast sailboats get close to 20 knots but seldom go faster. Spray drag is kind of like hull speed in this regard. To shed spray, the chine has to be at a fairly large angle to the flow.
    As far as stability goes, waterline beam is waterline beam and the water really doesn’t care what shape that beam is. A chine hull form may be wider at the waterline, or have a momentary increase in waterline beam compared to a smooth cross section, but the chine itself has nothing to do with it.
    SHC
     
  10. wet feet
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    wet feet Senior Member

    Westerly used to incorporate a moulded knuckle in the forward sections of their boats to deflect spray.Not that any of them would have had a problem with the drag increasing at a boat speed of 20 knots....
    Bolting on a spray rail might be feasible and bonding one in place might be even better as you would avoid adding holes through the hull.Bolting on chine that fairs into the surface would be altogether more challenging.

    [​IMG]
     
  11. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    I think the chances of a grafted on chine making a noticeable improvement in the performance of that Sandpiper range from slim to none. My guess is worse performance is as at least as likely an outcome as better.
     
  12. SuperPiper
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    SuperPiper Men With Little Boats . .

    Steve, that makes a lot of sense. You are a beacon and you're shining light on this issue. Thanks.

    Just to be clear, I was considering adding the spray rails along the aft 1/3 of the hull. Perhaps they are no longer called spray rails. Is there a better description of the rails in that location?
     
  13. Steve Clark
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    Steve Clark Charged Particle

    It’s a chine.
    It will not improve your boat.
    In order to deflect flow, the chine has to be at an angle to the flow.
    All you will be doing is adding wetted surface area.
    SHC
     
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  14. SuperPiper
    Joined: Jan 2003
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    SuperPiper Men With Little Boats . .

    Well don't you know? I was sailing a neighbour's Hobie 14 today. Each hull had the deck flange typical of many dinghy designs. Are deck flanges similar to spray rails?
     

  15. gggGuest
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    gggGuest ...

    They are primarily there for ease of construction and to a lesser extent off the water handling.
     
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