Automatic keel trim tab?

Discussion in 'Boat Design' started by BTG YACHT DSGN, Dec 22, 2009.

  1. BTG YACHT DSGN
    Joined: Oct 2008
    Posts: 104
    Likes: 3, Points: 0, Legacy Rep: 38
    Location: Poland, Warsaw

    BTG YACHT DSGN -sailing is believing-

    My idea is to attach to the keel's trim tab a lever ended with some lead. As the boat heels the lead according to gravitation moves to lover point (somewhere in the keel space, between frames) and by the lever rotates the tab in order to generate higher force on the keel...

    I'll try to make a 3D model of my idea soon, but now I'd be grateful just for your first imression on that concept...

    Primarily I'm going to use it in a scale RC boat.

    Regards,

    Kuba
     
  2. mark775

    mark775 Guest

    My impression is that it may flop around, it won't do much until a high rate of heel, then it will interrupt and make turbulent the water flow. In all, a detractor. Good luck and keep innovating!
     
  3. Tim B
    Joined: Jan 2003
    Posts: 1,438
    Likes: 59, Points: 0, Legacy Rep: 841
    Location: Southern England

    Tim B Senior Member

    You could do it with an electric servo and a tilt indicator, though you may need to apply some clever electronic trickery to ensure that you get a pure tilt angle.

    In theory it's a good idea, but I suspect it will take a little while to make it reliable. You also need to remember that gaps in foils destroy L/D performace, but making the gap as small as physically possible, whilst fine on a model yacht causes problems with fowling and cleaning on a full-size yacht.

    Keep coming up with plans though!

    Tim B.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I don't think it'll flop around, but it does have to be fixed or it will just follow the streamline flow paths of the boundary layer. If it was fixed it would "wander" around as the pressure gradient rose and fell on each side, but the keel wouldn't be terribly affected.

    You need a way of fixing it in position so the flow over it can use the tab as leverage, rather then just push it aside as it moves over it. This could be as simple as a fluid dampened coupler (shock absorber) to slow the reaction of the counter weighted tab or a full up mechanical linkage that is helm controlled like that on 1967 AC winner Intrepid (US 22).
     
  5. Doug Lord
    Joined: May 2009
    Posts: 16,624
    Likes: 305, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Couldn't you use a switch at the boom to activate a servo upwind with a radio circuit to center it downwind? See if Lester Gilbert has looked at this-design of the keel fin and trim tab will be critical at the low RE's of models:
    http://www.onemetre.net/
     
  6. tom28571
    Joined: Dec 2001
    Posts: 2,471
    Likes: 113, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    What is your vision of what the tab will accomplish if it can be made to work as you wish?
     
  7. BTG YACHT DSGN
    Joined: Oct 2008
    Posts: 104
    Likes: 3, Points: 0, Legacy Rep: 38
    Location: Poland, Warsaw

    BTG YACHT DSGN -sailing is believing-

    Thanks for your opinions.

    I 'll try to put a quick render of my idea as soon as possible.

    Regarding servo- the reason of this lever and weight lead and or other ,,mechanic" not electronic stuff is considered because of maximum simplicity I want to achieve in work of this mechanism.

    The general assumption is (not completely but quite logically true) that the the more yacht heels the more power from keel it needs (counteracting the power of sails) -----> so the tab need to act at greater and greater angle changing the profile from symetric to asymetric.

    Clever, huh :D (Who am I trying to impress..? ;/)

    -.- Ok, back to 3D modelling of this keel...
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A simple "on/off" switching system wouldn't offer the full benefit of this gadget. The trim tab's angle of incidence would want to be different depending on heel, boat speed, etc. to be most effective.
     
  9. BTG YACHT DSGN
    Joined: Oct 2008
    Posts: 104
    Likes: 3, Points: 0, Legacy Rep: 38
    Location: Poland, Warsaw

    BTG YACHT DSGN -sailing is believing-

    I'll see how simple mechanical solutions can control the correct position and amount of rotation (angle of attack)...

    I have to think about this...:idea:
     
  10. Doug Lord
    Joined: May 2009
    Posts: 16,624
    Likes: 305, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

  11. tom28571
    Joined: Dec 2001
    Posts: 2,471
    Likes: 113, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    As I see it, the function of the keel is to stabilize the boat with its weight and to counteract the side force of force of the sails. In actuating the tab as you intend, it may add a bit to the righting moment but it would also detract from the leeway resisting force. Not a good trade off, I'm thinking.

    Previous use of tabs on keels have been to counter leeway while the small reduction in righting moment was ignored. Keel mounted rudders have always acted this way.

    Maybe I'm not seeing your system correctly, but it looks like a no go to me.
     
  12. Doug Lord
    Joined: May 2009
    Posts: 16,624
    Likes: 305, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Tom, I may be wrong but I read it that he is talking about moving the back end of the trim tab to leeward? That would be the right direction... I think that by "power from the keel" he means greater resistance to leeway is required with more heel, correct BTG?
     
  13. BTG YACHT DSGN
    Joined: Oct 2008
    Posts: 104
    Likes: 3, Points: 0, Legacy Rep: 38
    Location: Poland, Warsaw

    BTG YACHT DSGN -sailing is believing-

    Yes, it should move to the leeward. How could it go otherwise ;).

    Anyway- I made a quick sketch, I hope that you'll read something from that...

    [​IMG]

    After all I started to considering putting, instead of these double lever as on the sketch, some lead into the trailing edge of the tab. The effect should be the same, but I'm not sure wheter the weight of the lead in the trailing edge would generate enough moment for tab to work properly (act stable).

    But the double levers seem to work better and should be more reliable...
     
  14. Doug Lord
    Joined: May 2009
    Posts: 16,624
    Likes: 305, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I was wondering how it was going to work-good idea but you might want to consider the other points that have been made. You know gybing boards are used on some dinghies- using the side force itself to move the whole board. You might consider a pivoting ballast keel -since it is for a model- that works on the same princible as the gybing board on a dinghy. Might be simpler and more robust.

    check this out: http://www.boatdesign.net/forums/boat-design/gybing-daggerboard-5783.html
     

  15. BTG YACHT DSGN
    Joined: Oct 2008
    Posts: 104
    Likes: 3, Points: 0, Legacy Rep: 38
    Location: Poland, Warsaw

    BTG YACHT DSGN -sailing is believing-

    So, you mean, that the hole keel should act like a gybing board? I'm afraid that the side force will be too small to ,,twist" the keel and additional vortices may occur on the ballast bulb... but perhaps some calculations will clear my way of thinkicg on this... :)
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.