ballast hung on a flexible keel...

Discussion in 'Sailboats' started by Schoonner, Jan 24, 2012.

  1. Schoonner
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    Schoonner Senior Member

    This is my idea, I want to make a boat like the K800 that can do well in waves.

    Think about this, I want t make boats like the K800 be like a live-aboard you can go to Hawaii on.

    How about a long mast like keel that is flexible like on a thick rubber daggerboard that is 20 ft long. You could support the mast with removable rigging, make an extra couple of layers of fiberglass on the hull and deck inside and out, and then raise and lower the ballast when hove to or not going anywhere and it would come up on either side of the mast you wanted. That way it would be like pulling around a suspending fishing lure attached to the bottom of the boat and exert force to keep it trimmed.

    Humm, Don't try going fast with it down too far or you might break it off.... Have to do something about that too.

    Maybe make the equivalent of brakes... YEAH! don't want to hit something with the hull? just drop down the keel and split the front open along it's length stopping the boat. humm might sink her... not a good idea. =0)
     
  2. gggGuest
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    gggGuest ...

    Well, it would be a formidable engineering challenge, but I guess those are there to be solved, but for some reason, given the thought of a ballast weight moving separately to the hull movement the words "horrendous seasickness" came to my mind.
     
  3. Schoonner
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    Schoonner Senior Member

    Actually, I think, that at the right length and stiffness it would probably damp the roll and trim motions more than usual.
     
  4. gonzo
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    gonzo Senior Member

    If the keel flexes the righting arm shortens. In other words, the more you heel the less righting moment you have. It is the opposite that you need on a sailboat.
     
  5. Schoonner
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    Schoonner Senior Member

    if the keel is as long as the deck it would have to flex right?
     
  6. gonzo
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    gonzo Senior Member

    Maybe I am not following. Can you post a drawing?
     
  7. Schoonner
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    Schoonner Senior Member

    This is the idea:

    A slanted daggerboard that can be raised and lowered. All it does is provide extra balance way down low changing the vertical center of balance. Because it can be lowered to about 20 ft below the hull it doesn't have to be more than say 500lbs so it keeps the boat light. It has to be able to flex a little though because if it doesn't it will probably just break off or crack the hull.

    I angled it back a little thinking that if the bow wants to raise up a little it would pull in a more straight up and down manner so it would be able to trim with the waves better. Then again, if it was not angled, it would not have the mast in the way. It might make the boat slower, but it would add considerable stability in big waves and maybe allow a harbor queen some coastline activity. You could just raise it up if you wanted to put the boat on a trailer and then you could remove it and install a more normal daggerboard for regular harbor cruising.

    Here is a pic, the darker part would be the lead ballast sticking out of the rubberized daggerboard and would be the part that would be submerged if just cruising around the harbor.

    It's kinda like a guy on a tight rope holding a pole. Whether or not it is all the way down, it will provide roll damping. You would have to stop to raise it up because the flex in would jam it in it's housing, but maybe be able to lower it while moving slowly.
     

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  8. gonzo
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    gonzo Senior Member

    It should flex the least possible. If it breaks or cracks the hull there is a structural defect or a bad design. At 20 feet it will get in the way of the rigging, create windage and make the boat unstable when it is up. The rake won't make much of a difference on the pitching. That is more a function of hull shape. A canting retractable keel would be a more efficient system. Also, it would allow you to sail the boat in shallow water. With this design once the board is up, It will interfere with the rigging and you'll have to motor or row.
     
  9. Schoonner
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    Schoonner Senior Member

    Okay, Thanks.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Dss

    -------
    Schoonner the best system I've seen so far that increases righting moment(RM) while keeping the weight low is Hugh Welbourn's Dynamic Stability System. It is a foil located about just below the waterline that extends to leeward and creates vertical lift as speed picks up. Adds RM equivalent to or in excess of any canting keel system.
    http://www.boatdesign.net/forums/sailboats/quant-28-foil-assist-keelboat-dss-38421.html
     

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  11. Schoonner
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    Schoonner Senior Member

    COOL!! I like that one! It requires speed and I want my boat to be more passively stable though. Humm... Maybe if they curved making shallow angles and float like little fin shaped amas it would be cool. I think that is the right name... The result would be a mix between.... HUH! I just thought of something that might even be better... Kinda a compromise if you will... wait, aren't ALL boats Compromises between opposing qualities?:D

    I'll have to draw a picture. :D
     

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  12. Schoonner
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    Schoonner Senior Member

    Okay, so mine are way too high... I just looked at the other ones and they look like they would be near the waterline.

    Is there a way to make epoxy not get too hot for a foamular rigid foam so I could make a pair with a foam center? I think I remember reading about a hull that was foam sandwiched in flass, but then I read how hot resin is supposed to get and I don't think that is a good idea for something like a foil that you want the exact perfect shape.
     
  13. Schoonner
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    Schoonner Senior Member

    Here, these are better. They are what I would call a laminar flow foil that is extruded outward and then curved as if starting to curl into a tube and pointed downwards with the ends trimmed into an efficient shape.. I will call them amas, but I don't know what they really are, and this is not really a good shape yet since they would try to tear themselves off the hull. I want them to fold downward having a strong hinge so that when the boat is launched with a trailer they will swing upwards and do nothing but float along along side of the boat and are not too wide to go down the road when she is hoisted out of the water letting them hang. (Probably a good idea to tie them down, they are foils that generate lift afterall:D) They are foils bent into a vertical in the picture, but they will see forces trying to pull the hull apart or downward when heeled over so it is not realistic!!! Do NOT try to make them from the picture! They just might,however be perfect closer to the boat. Idk, I don't know how to use a good hydrostatic program or even know if this could be accurately modeled.

    EDIT Humm, the pics did not post...

    Trying again
     

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  14. Schoonner
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    Schoonner Senior Member

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  15. harry cassin
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    harry cassin Old Salt

    Very Speedy looking :D
     
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