This comes at a hefty price, but seems impressive.....

Discussion in 'Stability' started by Mr Efficiency, Sep 11, 2020.

  1. BMcF
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    BMcF Senior Member

    You've hit upon an interesting aspect of the active motion control solutions; all of them perform better and do more amazing things with hulls that are more tender, statically, and more lightly damped in pitch and/or roll, dynamically. The SWATH is an iconic example of that, taken to the extreme. While very tender statically, they become phenomenally stable platforms when underway with a well-designed active stabilization system. We've also provided stabilization packages to a number of slender high-speed mono hulls that produced very good results and excellent overall vessel performance.

    The downside, of course, is what happens to such tender and marginally stable designs when the stabilization system quits working for any reason..... There is an analogy in the world of fighter aircraft. Highly agile aircraft have been made possible by incorporating features that make them aerodynamically unstable or marginally stable except for the highly complex real-time flight control systems they rely on. At least in the vessel world, we do not have far to fall when the stabilization quits.... ;-)
     
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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    How much power do they draw, as in the case if the boat shown at the beginning of the thread, and is it variable according to water conditions ?
     
  3. BMcF
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    BMcF Senior Member

    I don't know off the top of my head, since we've never worked with any of their gyros directly. I'd bet the specifications for weight, power and physical envelope are found on their web site though.
     
  4. missinginaction
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    missinginaction Senior Member

    See my post (right after your original one). The larger models must draw somewhat more power. You'd need at least a small generator to keep a Seakeeper going at anchor. Based on Seakeeper's website it works on the gyroscope principle. I believe it would draw the most power as it spools up to it's operating RPM. The little one looks to draw about 600 watts as it gets going and then less as it stabilizes.

    The power use I quoted you is for the small Seakeeper 1.
     
  5. BMcF
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    BMcF Senior Member

    The key to how effective their gyros are is the "active element" where they rotate the entire gyro ball with a cylinder, to create an even larger force opposing roll rate and roll motion than a simple spinning gyro would/does. I'd guess that the power required by that servo-mechanism is the driver behind the continuous total power required.
     
  6. missinginaction
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    missinginaction Senior Member

    There's a flywheel in there. It's horizontal, anchored at the top and bottom of the ball. More complex than a simple gyro but the laws of physics are what they are. They explain it (sort of) at their website. Seakeeper says that its gyros spin at "up to 557 miles per hour". That works out to 49,000 feet per minute. Say the flywheel has a diameter of 2 feet (I'm guessing but it's in the ballpark). That gives us a circumference of 6.28 feet. 49,000/6.28 gives us a maximum RPM of about 7,800. I don't know why they forced me to do the math to get an RPM figure. Maybe some marketing guy thinks 557 miles per hour sounds more impressive.

    It looks to me as though the hydraulics are there to dampen the fore and aft pitch, keeping the Seakeeper as level as possible as the flywheel resists the rolling tendencies side to side. I'm not a physicist but I believe that if you keep the spinning flywheel in the same plane as the boat you'll get better stabilization. In addition you wouldn't want to inhibit a boats ability to raise it's bow into the waves or recover from a following sea.

    I'm not knocking the product at all. If you get seasick a lot this is going to be a game changer for you if you can afford it and fit it into your boat. My problem isn't seasickness. After a couple of days on the boat I'll get off and when on solid ground the whole world feels like it's moving for about a day. I don't get "landsick" but I notice it. Maybe I should just stay on the boat? Self isolation?

    MIA
     
  7. BMcF
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    BMcF Senior Member

    No, that is not how it works.

    The gyro force opposing the roll motion is proportional to the roll rate imparted on it. The key to the effectiveness of the Seakeeper gyro is how they measure roll rate and use that, processed through a control system, to amplify the roll rate the gyro experiences, thus creating a much larger roll damping moment than would be gained from a gyro that is simply bolted down and spinning.

    Back in the mid-90s, when the developer of the Seakeeper and I were part of the same company, we'd started noodling the design that is now that gyro. A Dutch colleague named Theo Koop had experimented with a number of "active" gyro and pendulum ship motion control inventions and that was where some of the ideas for Seakeeper came from. Me....I ultimately continued on with the development of flight control systems for hydrofoils and ride control systems for SWATH and SES primarily. I thought the gyro looked "boring" technically....little did I know what a success it would eventually become.
     
  8. missinginaction
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    missinginaction Senior Member

    OK, but help me out here. The hydraulics appear to adjust the orientation of the flywheel relative to the fore and aft pitching motion of the boat. The flywheel itself is horizontally oriented. I can see how the spinning flywheel dampens side to side motion.

    Where I'm confused is in regard to fore and aft pitch. You wouldn't want a device to prevent your boat from rising into a wave? You would not want a device to try to hold the stern down in a following sea either? I just thought that the hydraulics would allow the gyro to operate in a way that allowed a boat to pitch for and aft as necessary, yet dampen side to side roll. If I'm wrong about that maybe you could explain what it is that the hydraulics are actually doing?

    Maybe I used the word "level" incorrectly. Do the hydraulics attempt to keep the flywheel in the same plane as the hull of the boat? Not side to side but fore and aft. As the hull rose into a wave for instance, would the hydraulics pivot the flywheel so that it's position remained constant relative to the angle that the boat was at? In other words if the bow rose 10 degrees to climb a wave would the Seakeeper's gyroscopic flywheel assembly be rotated up ten degrees as well?

    Just trying to understand this.

    Thanks,

    MIA
     
  9. BMcF
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    BMcF Senior Member

  10. missinginaction
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    missinginaction Senior Member

    I did, but it's an advertisement. Again, I'm not knocking the device but would just like some additional detail on how it actually functions. I'm sure that in due time more user reviews/information will come out.

    Regards,

    MIA
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Gawd, I did read that post, but didn't remember the amperage mentioned ! :rolleyes: It does seem they would chew some power, so that has to be considered as part of the deal.
     
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  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Are we to understand these things work to keep the boat level, regardless of what axis ? Obviously in resisting athwartship tilt, it needs less ability to do so than in the long axis, to get the same correction, as most boat can be made to heel a lot easier to x degrees, than to change fore and aft trim by the same x degrees.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Another thought, could these devices be helpful in limiting hobby-horsing in slim-hulled catamarans ? They certainly do appear to offer new possibilities that otherwise would not exist.
     
  14. BMcF
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    BMcF Senior Member

    I'm not aware of the Seakeepers being marketed for or applied to damping pitch motions. Not that they couldn't add pitch damping if installed in that axis on a pitch-tender vessel.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Would it help a sailboat to keep the mast more vertical ?
     
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