Inertial driven fin stabilizers

Discussion in 'Stability' started by wheels, Jun 28, 2010.

  1. wheels
    Joined: Jun 2010
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    wheels Junior Member

    has anyone tried anything like this? it would be a weight suspended low in the hull connected to stabilizing fins. it would have fluid dampeners (think automobile shocks but longer) to control swing but allow the weight to counteract roll

    I was sitting thinking of a way to counteract roll without using power from engines and this is what I came up with. (if its been done before great but I haven't seen anything like it)

    [​IMG]

    if the boat rolls to the right the weight would kick the fins over and it would force the boat to right itself if hit by a wave from the right it would force the fin to the left pulling the weight to the right aiding in stability and moving the weight towards the wave shifting center of gravity into the impact helping to keep the boat level
     
    Last edited: Jun 28, 2010
  2. CDK
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    CDK retired engineer

    Your construction corrects roll by changing direction.
    In a choppy sea that would mean the boat would feel out of control: nobody likes that feeling.

    To stabilize a rolling hull, horizontally rotating fins are needed. They should act immediately, when a correction is made by a moving weight, the action is too late.
     
  3. wheels
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    wheels Junior Member

    Ok. I think i understand.

    Even if the fins are mounted more horizontally than vertically? It does make sense that there would be a "lag" in response but it wouldnt help? If it's a space issue for the weight, that's not really an issue for what I have in mind. But again thankyou for your input.
     
  4. tom28571
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    tom28571 Senior Member

    The idea does seem to have merit but I would use the energy to operate a trim tab rather than the whole vane. That would make the system much smaller and more sensitive. Vanes near the CLR would minimize steering moment. The damping action would be somewhat delayed but still could be effective to some degree.

    CDK, I think some hulls do counter rolling at sea by responsive steering. Looking at how the big cross (English) channel cats handled waves, it seemed that they did just that. Just my observation though.
     
  5. CDK
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    CDK retired engineer

    Yes Tom, you also do that yourself at the helm when something big is coming your way.
    But if I have a stabilizer system, try to keep a steady course and the boat ignores the steering wheel, I'd be quite upset, especially if the boat would wait until the wave hits and it already rolls before steering into the wave.

    With the sea coming from port, the boat would automatically steer that way after each wave hits, ends steering right into it and I'll never reach my destination.
     
  6. jonr
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    jonr Senior Member

    Various roll stabilizers have been done - gyroscopes, powered fin stabilizers, sails, weighted keels, weight aloft, etc. Your idea would be a non-powered fin stabilizer, which, IMO, limits the ability to optimize the control algorithm - computers can learn from the speed of roll onset, previous waves, etc to predict the correction needed before the roll fully develops.
     
  7. FAST FRED
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    FAST FRED Senior Member

    Not using "power" from the engine while underway is a strange goal as most engines have huge power to spair.

    Using 5A of 12V DC isnt going to slow most boats a bunch.

    My thought for stability is a center board , mounted in a wider than usual trunk.

    A near balanced trim tab at the rear would cause the board to pivot a few dig to create a good angle of attack for the well shaped board.

    Yes some power will be required for the surface area and working drag of the stabelizing board, but not much weight .

    A sailboat tiller cheapo ram style autopilot would be the actuator (OR ?).

    And running aground would NOT knock holes in the boat , or cause the separation of a $10,000 fin.



    FF
     
  8. BMcF
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    BMcF Senior Member

    Fundamentally, to reduce roll angle the force produced by fins must be responsive to and in opposition to roll angular rate. Rate preceeds angle by 90 degrees of phase lead. Any system like the pendulum system depicted is actually lagging even the roll angle, forget roll angular rate! As such..there is, in fact, the high probability that such a mechanical system would increase the magnitude of resonant roll in some vessels.
     
  9. daiquiri
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    daiquiri Engineering and Design

    Well said.
     
  10. Bubblehead
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    Bubblehead Junior Member

    Possibly a gyro could make sense? E.g., a single, vertical fin extending downward from the keel at the center of yaw. The post forms a yoke with a gyro wheel running (axis of rotation abeam at rest). Roll rate would cause the gyro to precess, turning the fin. Crazy?
     
    Last edited: Jul 8, 2010
  11. BMcF
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    BMcF Senior Member

    Now yr on to something. In fact, the original (no longer produced but still supported AFAIK) VDM/Naiad stabilizer systems for decades used that principle, although the gyro caused fin motion via hydraulic means, directing pressure to move the fin. The reaction force from a gyro is proportional to/resisting changes in angular rate; just whatcha need. ;)

    Modern stabilizer systems using MEMS motion sensor technologies and digital controllers have far surpassed the 'mostly mechanical' predecessor systems in terms of performance...but there was something to be said about the pure simplicity of some of the early solutions based on true spinning gyro solutions.
     

  12. BMcF
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    BMcF Senior Member

    The 'master-slave' fin or trailing edge flap actuation method that you describe is quite valid and, in fact, was 'invented' and proven out some decades ago by the same guy that built the stabilization system for the USN prototype SWATH, SSP Kaimalino. The large power requirements for moving large unbalanced fins was exactly what drove the solution.

    That last time I saw that master-slave tab 'trick' used in practice was on the huge 'lifting body' foils that were installed under the USN HYSWAC testcraft about 10 years back. Without the master-slave balance tabs, the loads on the control surfaces would have been astronomical at higher speeds.
     
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