Pivoting keel ideas?

Discussion in 'Sailboats' started by Roo2, Sep 8, 2014.

  1. Roo2
    Joined: Feb 2014
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    Roo2 New Member

    Hi,
    I'm looking for clever ideas for a fully retracting pivoting keel for my trailer sailer of 5.7m LOA. Fully retracting into a longitudinal trunk to make it easier to trailer launch, retrieve and beach. Ballast weight is about 200kg at 1.3m draft. I'm particularly interested in raising mechanism suggestions (e.g. cable, hydraulic).
    Thanks.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I think there are not any really new ideas. What do you have in it now?
     
  3. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Weighted centerboards have been around for a few centuries in this country and the methods to deploy and hoist are countless. A board as heavy as yours will need a self braking winch. You could use just tackle, but this is more trouble. There are other approachs, such as a ram, levers, actuators, worm gear, etc., but the best ones are usually the simplest as well. Which boat will this be going on?
     
  4. Roo2
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    Roo2 New Member

    The current design is an excellent and simple vertical fin with a torpedo bulb on the bottom that can be hoisted up with block and tackle from the cabin top. Very efficient but makes it harder to get on/off the trailer and beach because it still has draft when fully raised. I like the idea of using a hydraulic cylinder and hand pump but haven't found a neat setup yet so suggestions are welcome.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Hydraulic can work fine, but are more complex then necessary for the weight of this appendage. A simple winch is fool proof. You have a lifting keel, not a centerboard, so rotational hoisting isn't an option.

    Yes, these types of appendages do leave some draft showing, because the bulb can't retract fully, but without a garage, stub keel or other contrivance, you're pretty much married to it. The hoisting method could be changed, which can be simple or complicated.

    Which design are we talking about here?
     
  6. whitepointer23

    whitepointer23 Previous Member

    If you convert it to a swing keel it will suffer in performance as well as having an extra long center case in the cabin. When the swing keel is down you have a long slot behind the keel creating drag. With the drop keel you don't.
     
  7. PAR
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    PAR Yacht Designer/Builder

    It's a bulb on the end of a fin, so it's not possible to convert it to a weighted centerboard, unless the bulb was set on a pivot. This is an engineering nightmare, though possible, I'm not sure why you'd want this setup, as you'd still have the bulb tucked up against the boat's belly.
     
  8. whitepointer23

    whitepointer23 Previous Member

    Thats right. Am I correct in assuming the swing keel slot would cause extra drag. Because racing boats always have drop keels not swing.
     
  9. PAR
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    PAR Yacht Designer/Builder

    I saw a parallelogram sort of thing on a bulb once (two narrow fins), allowing it to swing up, with the bulb level, but what a contrivance.
     
  10. Jammer Six

    Jammer Six Previous Member

    The worst problem with hydraulics is that they can and will fail. Furthermore, they only fail in service.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Excellent point Jammer, though I've found hydraulics aren't guaranteed to fail so much as, guaranteed to not receive the routine maintenance they require, so they usually do die. If an owner is paying attention, he'll notice the symptoms prior to death and address them. This is the butt kicker with these systems, you have to stay after them or they'll pop a seal (or whatever) when you need them most.
     
  12. Roo2
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    Roo2 New Member

    Thanks for the replies. Sounds like I should avoid a hydraulic system. I'm prepared to compromise some performance for convenience. I'm wondering whether I can't get a bit back with a longer weighted centreboard and a trunk that goes all the way through to the transom...
     
  13. philSweet
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    philSweet Senior Member

    Roo2, without some photos of your boat, It is impossible to say more than already has been said.
     
  14. PAR
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    PAR Yacht Designer/Builder

    There's nothing wrong with hydraulics, if you keep up with them. In some cases, it's one of the few things that can work.
     

  15. philSweet
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    philSweet Senior Member

    As far as making life easier, I designed a fairly substantial weighted cb for a 40' sharpie. I planned to make the companionway frame a box that held a garage door spring on each side. One helped with the cb and the other helped with the mast which was carried on a tabernacle. I haven't ever seen it done, but pretty straightforward for a backyard builder, and yes, you can buy stainless springs. The mizzen had the spring in the mast tube. The weight of three springs wasn't much of a concern on this boat.
     
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