Canting Keel Mechanisms

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

  1. SuperPiper
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    SuperPiper Men With Little Boats . .

    This was discussed during the Vendee Globe.

    Why rely on hydraulic rams to cant the keels? Why not use a mechanical system? A rack & pinion? A lead screw? Pawl & ratchet? These devices could be hydraulically driven but once positioned, the keel would be mechanically locked. No "Free Willy".

    Is the degree of keel cant variable? Or, are there just 3 positions: centred, hard to port & hard to starboard? I would think that a system engineered to be driven and locked would be more reliable than a system engineered to be driven and held!

    Am I missing the big picture?
     
  2. the_sphincter
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    the_sphincter *

    with hydraulics, when they work properly, there is a pressure relief if the load gets too large for the structure or hydraulic system. With a screw, the friction effects would be tremendous
     
  3. fcfc
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    fcfc Senior Member

    In cars, mechanical brakes have been superceded by hydraulic ones more than fifty years ago. They only remain on bicycles. And not even all ...

    Hydraulic system are the simplest. (see chinese hydraulic jack prices). If you cannot built such system reliable, do not expect to have ballscrew, gears or other precision mechanical devices reliable.

    Do not forget that on theses race boats, one of the goals was that the canting mechanism do not weight way more that the ballast it lifts.
     
  4. usa2
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    usa2 Senior Member

    i think what they should do is have a hydraulic system for canting the keel, and a hydraulic system for holding the keel at the selected cant angle.
     
  5. cyclops
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    cyclops Senior Member

    When it gets rough and choppy ,a human can start the ram to the new correct position long before anything automatic could.
     
  6. RHough
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    RHough Retro Dude

    It is also a power required vs weight vs speed issue.

    In a small boat, a traveler type system might well be lighter and faster than a hydralic system.

    I think the VO70's are allowed to use an engine driven pump to move the ballast, in that case hydraulics win hands down.
     
  7. gonzo
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    gonzo Senior Member

    Check out this 1930's system
     

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  8. dougfrolich
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    dougfrolich Senior Member

    Canting systems can and are made to be reliable:
     

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  9. skiff sailor
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    skiff sailor New Member

    im not sure if many people here are femiluler with the sydney to hobart yacht race in australia but in the most recent race 6 out of 9 boats with canting keals failed and a 66 footer called aapt that has water ballests instead of a kanting keal and it was keaping up with boats 30 foot longer so i dont really see the problem with water ballests especially since there so much more reliable.
     
  10. RHough
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    RHough Retro Dude

    The quest for speed under sail has always created extreme machines. Solutions that work at one scale may not work at another.

    Moving ballast has been around for 100's of years. It's not a new concept. Every design is a compromise, the design that wins on a given day is the one that works the best under that days conditions.

    The only requirement that all race boats must meet is to float, after that its all debatable.

    As a skiff guy, you know that any form of ballast at all slows the boat down. Sailing speed only equal to windspeed would make a skiff a sure looser, yet it is a break-through for ocean racing.
     
  11. SuperPiper
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    SuperPiper Men With Little Boats . .

    The engineering paradox: hydraulic is best; but it ain't good enough?
     
  12. dougfrolich
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    dougfrolich Senior Member

    Robust and reliable canting and lifting and lifting/canting systems have been used in cruising boats with a very good service record for 5+years. Failures in race boats are a high profile event. Remember though, race boats are allways going to dance on a thin line, reducing safty factors to save weight, and sometimes that is done too aggressivly. The cruising boat is not under the same pressure, and therefore you have not seen catastrophic failures. So in my HO Hydrolic systems can be, and are engineered to be reliable, but race boats are allways looking to save weight and that has led to failures- which proves not that theses systems can't be made reliable but, that there is still alot to learn about dynamic loads in sailing yachts.
     
  13. dougfrolich
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    dougfrolich Senior Member

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  14. RHough
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    RHough Retro Dude

    Well said.

    When a yacht is sailing at speeds so high that little or no empirical data is available to base predictions on, the same light weight required to achieve those speeds is the safety factor's enemy.
     

  15. dougfrolich
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    dougfrolich Senior Member

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