Probably far from a new idea

Discussion in 'Boat Design' started by Southern Cross, Apr 1, 2013.

  1. Southern Cross
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    Southern Cross Senior Member

    To me, the IMOCA 60's strongly resemble the Aussie 18 skiffs. I used to race the 12' version as a kid. One of many obvious and discernible differences is the ballast systems. Both are moveable, however, in the case of the IMOCA 60, ballast is in the keel and contributes to drag (unless when hiked out and your *** drags through the water). I'm sure if the designers could figure a way to hike out ballast on a 60 they would have done it by now. It seems like Speed Dream is attempting a compromise between the two.

    I feel instinctually that extraneous and superfluous appendages on a boat will become a thing of the past. I cant imagine foils hitting a UFO at the speeds that are being made. But that goes more to my other post about "morphing hull forms". This isn't an argument about the benefits of foils and multihulls, though. I just wonder if it is possible ...

    Say you started the design process with a ballast system, a moveable but internal ballast system and then built the hull form and designed the sail/wing plan based on the weight of the ballast system and all other components (if a boat has little to no displacement what is the total weight of the boat called?). This is probably a common approach to design. I don't know...

    If you could put the canting keel ballast inside the boat, pivoting from a lever at deck level, riding on a track from center line all the way up port or starboard, below deck, wouldn't this, to some degree replace "rail meat"?

    I'm just thinking that if you removed 15' of keel and so much ballast on a bulb, you could eliminate some form and frictional drag. Lateral resistance and steering could then be accomplished with chines and removable fore and aft foiling dagger boards or just stick with the same dual rudder systems already being used.

    Safety. The canting keel would have to be enclosed in a carbon case probably just aft of the mast. Accommodations would be limited to the space aft of that. The keel could be locked into position to gain access forward through hatches which would be limited to repair and other similar situations.

    There is a whole lot of math needed to find the optimal size boat for this configuration, the perfect balance. Clearly, you don't have to be big to be fast. A hull with less drag would need less energy to move it, no?

    Lets say you start small, with say 2000 lbs of lead ballast (10 big dudes) incased in a carbon cylinder riding on rails. The cylinder would have to accommodate 5,128 cu. inches of lead? If the cylinder was 36" in diameter it would have to be around 90" long, yes? The hull form would have to accommodate 90" + at this particular point in the beam. 2000 lbs plus the weight of the hydraulic arm and the carbon case = ? ( I apologize in advance for my wretched math skills). Also, the hydraulic arm would have to telescope to accommodate the shape in the hull (greater distance from center to beam than center to floor).

    So, then ... how long would the boat have to be, 20' or 40', how big of a sail plan, what sort of dagger boards and where would they be positioned to keep this boat upright and planing across oceans? Would you need any keel at all? Could you foil a boat like this?

    Sorry for the sketch. Using my kids colored pencils.

    Don't shoot the dreamer!!!
     

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  2. messabout
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    messabout Senior Member

    That is an idea that contains some degree of logic as well as fertile imagination. Whether practical or not is to be determined. There will be wicked structural problems to overcome while attempting to keep the weight and complexity of the considerable mechanical components to a reasonable minimum. If that 2000 pound thing ever got loose it would be hell to pay, so it had better be a failure proof mechanism.

    Where do we get the hydraulic power?.....From a substantial pump no doubt. The pump would need a lot of volume per unit of time if we are to tack or maneuver reliably. On a smaller scale this could be done mechanically of course....winches, blocks, lines and so on.

    This is a modernistic upgrade of the old time sandbaggers methods.
     
  3. Southern Cross
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    Southern Cross Senior Member

    Thank you for being open minded. I think I have been put on every ignore list in the SA forum for discussing things like this.
    Speed Dreams ballast is not that much further outboard...
     
  4. Doug Lord
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    Doug Lord Flight Ready

    =============
    Don't let the naysayers get you down: I was very pleasantly surprised when after publishing my ballast "wing"(Trapwing) on SA and being ridiculed by people who ,for the most part, didn't understand it, Julian Bethwaite published a design for a 60fter using a system for on-deck movable ballast for his "Pterodactyl" concept. He later encouraged me with the Trapwing like the first class guy he is. I'd suggest that your idea would probably work but would require some of the same mechanics that would be necessary to move the weight much further to windward. There could be designs where your system would be ideal in that it reduces drag a lot, but the problem with making it self-righting would be difficult. You would still need a daggerboard and rudder. You might be able to use a very small keel bulb just enough for self-righting and use your system for "rail meat". I don't see the complications of your system as too great at all considering some of the canting keels systems I've seen. Don't hesitate to build a model to test it-that system would be able to be tested in a relatively small RC model. Keep thinking!

    Not exactly what you're talking about but some ideas for high performance disabled sailing including on-deck movable ballast that slides in a sealed "wing":
    http://www.boatdesign.net/forums/sa...isabled-physically-limited-sailing-37048.html

    And a relatively new take on the canting keel: http://www.boatdesign.net/forums/sailboats/flying-canting-keel-extraordinary-innovation-30806.html
     

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  5. TANSL
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    TANSL Senior Member

    I do not know if I have misunderstood this but I think the keel, as well as a counterweight, is used to prevent drift. I do not think it's good to eliminate them, in monohulls. Furthermore, the fins articulated at its base and there. I apologize if what I say is a too big nonsense.
     
  6. Southern Cross
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    Southern Cross Senior Member

    It is really something not be shot down. I think about this stuff all the time and/so it's nice to be able to share it.

    As I have zero training, I don't have any answers to any of the engineering issues. If someone wants to run with it, please do. All I ask is to watch and if ever it comes about, go for a ride.

    Is making leeward less of an issue at speed? So a thinner, shorter foil type dagger board or two could compensate for a keel?
     
  7. Southern Cross
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    Southern Cross Senior Member

    Doug, thanks for pointing those things out and the other post. Hmm. More to think about.
     
  8. DCockey
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    DCockey Senior Member

    A disadvantage of having the movable ballast inside the hull is the maximum righting arm of the movable ballast is limited to less than half the beam.

    My understanding is most boats with swing keels, including SpeedDream have separate apendages to counteract leeway.
     
  9. Southern Cross
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    Southern Cross Senior Member

    You are referring to the ability to right itself? Yes, that's a big problem. Thinking about it.

    Could this system replace a water ballast one? Lead heavier than water etc
     
  10. TANSL
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    TANSL Senior Member

    The general idea of the PO seems good but I want to expose a pair of points for your consideration :
    - The liquid ballast can be tricky to handle. (free surfaces effect)
    - Solid ballast inside: how to handle the inertia of the moving masses?. In trying to control the inertia can cause the ballast stabilizing effect is not instantaneous
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ===============
    It probably could but it wouldn't have one of the advantages of water ballast: being able to get rid of it.
    --
    You would definitely need a something like a daggerboard and rudder.
     
  12. DCockey
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    DCockey Senior Member

    Usually the reason sailboats carry ballast is to counter-act the heeling moment from the sails.

    Internal lead ballast could replace a water ballast system. One disadvantage of an internal movable ballast system is the compartment containing it would probably divide the interior of the boat.
     
  13. gonzo
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    gonzo Senior Member

    Internal water ballast has been used for a long time, and all the bugs are pretty much worked out for them. A sliding solid ballast is not a bad idea at all. It could be worked with block and tackle and a ratchet system. The ratchet to let the ballast free fall to the center as the boat tacks to speed up the change.
     
  14. Southern Cross
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    Southern Cross Senior Member

    I like the practical application of it.
     

  15. TANSL
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    TANSL Senior Member

    The liquid ballast is used only when it comes to maintaining a certain depth or some trim, when the ship carries no load. When the boat is loaded, the ballast is removed. This is the only reason that justifies the liquid ballast. Effectively exist stabilizers devices based on liquid ballast. When used in this way, you need to place special devices (connected vessels, valves, longitudinal bulkheads, to prevent or reduce the free surfaces). When used to get a specific trim or depth, should be avoided ALWAYS the effect of free surfaces. A fixed ballast weight should NEVER be done with liquids. It is nonsense because with much less volume, about 7 times less, a solid ballast has the same effect.
    An internal solid ballast can be controversial, since its conditions can adversely affect the stability of a ship. You have to make the move the ballast towards port side when the ship heeling to starboard and vice versa. It is not easy and, of course, impractical.
     
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