A canting keel with a hollow bulb?

Discussion in 'Boat Design' started by trip the light fandango, May 28, 2018.

  1. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Junior Member

    After reading the post on canting keels and how weight stops planing, I began to wonder why there aren't keels with torpedo shapes hanging off the end filled with air/ or water ballast ratio if needed. I have a mate that reckons every 5th idea I have is a ripper, I guess that makes me dull company.. it's a long wait...ha ..err. My first feeling is that the pressure of the bulb wanting to rise to the surface would be greater than any forward momentum gained by the sail, so the yacht would end up tipped to the lee side abeam of the wind stopped dead,or would just circle the bulb/ float[not so sure about this now]. Secondly that the keel would cease to act as a keel and would become an attached float which may be feasible if it can reach an angle that sets it on the waters surface[proa]. this may work but it would need fins or dagger boards to gain direction... One interesting point is that it swaps sides depending on whether it is filled with air or weight. Also that if it can reach the surface the yachts draught would be more like a shoal draft at anchor. Lastly 1 tonne of displacement [35ft yacht] in a torpedo tube is a sizeable thing..lets say 1 cubic metre plus the weight of the torpedo itself is significant drag, extra length having a few issues too. Does this make the craft not a monohull? I suppose if the bulb reaches the surface it becomes afloat ,then it's a proa.

    I would consider making a model but I stumble reconciling how water can't be scaled down in density[fresh would help a bit] so tests won't achieve much or maybe anything ,in this case. I'm a little befuddled ,surely someone must have thought of and made this.
    ed, thanks Doug for the input.
     
    Last edited: Jun 1, 2018
  2. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    You must have miscounted. :D
     
  3. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    on one hand lighter is better than heavier

    on the other, lighter only gets you density of water, where as lead gets you 11x that and hence less surface area

    on the other hand hollow wont drag you straight to the bottom if things go sideways
     
  4. trip the light fandango
    Joined: Apr 2018
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    trip the light fandango Junior Member

    The idea hasn't been chopped down yet...and besides more will pop up,..like the flywheel positioned midship along the keel, solar driven..ha ,cheers
     
  5. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Junior Member

    I suppose the float/ torpedo wouldn't affect the mono's ability to reach unless it is running on the surface., answer ,- until a 45degree angle the canting works as a keel, thanks Dolfiman.
     
    Last edited: May 29, 2018
  6. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Junior Member

    Asking a question like this and getting no clear negative response reminds me of playing Cluedo..
    As a community it seems no one has Colonal Mustard in the billiard room with the revolver.. It seems like this idea floats ,, someone definitively sink it please..
     
  7. CT249
    Joined: May 2003
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    CT249 Senior Member

    1- water's density is so low that a useful bulb would be enormous and therefore have vast drag.

    2- If the fin and bulb are strong enough for the structural load, they will be heavy even if filled with air.
     
  8. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Junior Member

    I suspect you are correct, using a gas might change the weight issue a little but I'm not really interested in carrying another gas that is probably flammable or poisonous to breathe in. I don't have the money to spend on carbon fibre either. I haven't completely given up , there may be a way still,.. thanks for the frank assessment. But the fin and mechanism need serious strength, but not quite so much the bulb.but it would need to be quite long ,..more strength required.. still thinking ,.. ha ..regards .
     
  9. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    On the IMOCA raceboats the canting keel pivot axis is angled up so that the front end is higher than the aft end. This changes the angle of incidence of the canting fin so that it creates vertical lift. The vertical lift slightly reduces RM but in combination with the lee hydrofoil the net effect is to reduce displacement and wetted surface.
    You could consider a version of your concept with the pivot axis angled the opposite way so that the keel fin produces downforce the more the keel cants which would increase RM and, at the very least, reduce the amount of ballast required in the canting keel bulb.
    Keep this in mind: the use of lift(downforce) from foils on keelboats has NOT been fully explored yet.
    In case you haven't seen this:

    IMOCA sketch from yachting world.png

    Stravaganza with flying canting keel:

    Canting keel-Flying Canting keel.jpg
     

  10. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Fandango,
    How about pumping mercury in and out of the bulb?
    Or pushing it out with helium...?
    You go you outside-the-box thinker!
     
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