Canting Keel Mechanisms

Discussion in 'Sailboats' started by SuperPiper, Dec 1, 2005.

  1. SuperPiper
    Joined: Jan 2003
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    SuperPiper Men With Little Boats . .

    I guess I have a personal bias against hydraulics.

    Car brakes are hydraulic. But, an automatic transmission is mechanically locked in PARK and a handbrake is always mechanical. I have seen those inexpensive hydraulic jacks creep down as fast as they can be pumped up. Ultimately, the entire system is relying on a rubber seal to hold 1000s of pounds of force.

    Mechanical systems just don't seem to leak into the bilge when you need them most.

    What do aircraft use to manipulate control surfaces?
     
  2. RHough
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    RHough Retro Dude

    But, an automatic transmission is mechanically locked in PARK and a handbrake is always mechanical.

    The requirement to lock the output shaft is completely separate from the drive function. In an auto trans, hydraulics are used for two functions, torque multiplication (inside the torque converter), and to engage mechanical couplings at different gear ratios.

    The hand brake is required to act as an emergency braking system. It is separate from the service system so it will operate if the service system fails. Using a mechanical system is cheaper.

    If hydraulics are less reliable, why are they preferred as Primary Systems?

    I have seen those inexpensive hydraulic jacks creep down as fast as they can be pumped up. Ultimately, the entire system is relying on a rubber seal to hold 1000s of pounds of force.

    Are you surprised when cheap junk does not work?

    Compare the area on the ram to the seal area. Where is most of the load? Most jack creep is not due to external leaks, but due to the failure of a mechanical valve.

    Mechanical systems just don't seem to leak into the bilge when you need them most.

    Please sight a case where a hydraulic system has evolved into a mechanical system for reliability reasons.

    What do aircraft use to manipulate control surfaces?

    I'll bite ... Pilots? :)

    I'm guessing that primary flight controls still have mechanical back-ups. I'm also guessing that flaps, spoilers, and wheel brakes are hydraulic.
     
  3. gonzo
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    gonzo Senior Member

    Aircraft systems are hydraulic. Most heavy machinery is too.
     
  4. SuperPiper
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    SuperPiper Men With Little Boats . .


    OK, I'm stuck.

    Maybe ask me again in 2009.
     
  5. usa2
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    usa2 Senior Member

    I believe it was mentioned earlier in the thread that a mechanical way of canting the keel was unsatisfactory due to no pressure relief. That is true, as i was involved in the design of a derivation of L. Francis Herreshof's Sailing Machine-a 42 foot sailing canoe with a canting keel. He had designed a worm gear system to cant the keel, and it was found that if a mechanical system was used instead of a hydraulic, the mechanical system would destroy itself and then the hull of the boat due to shock loadings.
    The boat was never built, but this was very insightful into one reason hydraulics are favored over mechanical means in canting keels.
     
  6. K4s
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    K4s Junior Member

    Hydraulics seems to be the answer to the canting motion,but,the problem seems to be with the amount of shock loading the systems have to bear.Is there not a suspension system incorperated within these canting systems,like the suspension on my mountain bike,to alleviate some if not all of this shock loading.If not why not.It may wiegh a bit,but less detrimental than total keel failure I would have thought.
     
  7. fcfc
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    fcfc Senior Member

    Shock limitation on a hydraulic system is just a pressure relief valve. Shock absorber on your car are nothing more hydraulic systems (with a calibrated one way valve).

    Hydraulic canting system can be safe. That s just any racer would laugth when he would weigth it.
     
  8. yipster
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    yipster designer

    records are broken but i still have to get used on this canting keel design, maybe i dont like asimetric, i dont know what it is...
    keel lift was discussed but i remain curious to see how little lift to area attached sketch is.
    how do ruddering keels compare to canting, dont think weve seen the end of this devellopment yet
     

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  9. Doug Lord

    Doug Lord Guest

    "ruddering keel"

    What is a ruddering keel? Whatever it is you're 100% right: there is a lot more development ahead in canting keel systems....
     
  10. yipster
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    yipster designer

    ai. by ruddering keel i mean a wide stern, pivoting keel, or keel with rudder like the pics in the keel lift thread
    when you take a good look you can see project amazon having a rudder behind her keel ( as in the drawing below it )
     
  11. Doug Lord

    Doug Lord Guest

    Thanks!

    Got it! I understand that (generally) as a trim tab though CBTFco has taken the concept one step further by using the "trim tab" to generate downforce with a high cant angle fin.Lot's more potential in the design of canting systems..
     
  12. usa2
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    usa2 Senior Member

    I actually dont think that is a feasible idea for racing sailboats, because the trimtab would be creating an enormous amount of drag while creating lift. So basically your boat would stay upright and go slower. CBTF and TMF or whatever you want to call it or probably the most refined systems you will get...now all the designers can do is cant the keel to a higher angle and/or reduce wetted surface if they want to improve the designs.
     
  13. Doug Lord

    Doug Lord Guest

    "trimtab" down force

    I imagine CBTFco, Alberto Calderon and a few others including me would say you're very wrong about that.
    ------------
    The Lift/Drag ratio of something like this is, of course, very important.The system has been tested
    and found to work well.
     
  14. RCSail
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    RCSail Junior Member

    When Hobie was working on their trifoiler they found that it was faster to have the upwind hydrofoil producing negative lift rather than to depower the sail, even though the hydrofoil was asymmetric and quite inefficient at negative AoA. At any given speed it would be faster to have the weight produced by a trim tab-equipped keel with more weight in the bulb, but using a trim tab would permit carrying a greater press of sail in heavy winds without undue weight in light winds.
     

  15. Doug Lord

    Doug Lord Guest

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