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  1. vibroman

    Canting keel forces

    I gotcha Seems like a single acting ram system would be more robust (only working in compression). Also hard to design a support structure that is equally efficient in both compression and tension. Are all the systems double acting or are the ABN boats using a single acting system?
  2. vibroman

    Canting keel forces

    Do we know the failure mode of the hydraulic systems? Are the cylinders bursting due to over pressure? Are the seals failing due to overpressure or are the rams snapping? Hard to see how a ram could fail due to pressure surges in the susyem as the load from the hyraulic pressure is all...
  3. vibroman

    Canting keel forces

    The accumulator itself usually consists of a nitrogen filled bladder inside a pressure chamber. This actually introduces a significant damping component to the system instead of stiffness (and therefore less response to external excitation). Accumulators also provide reserve pressure inthe event...
  4. vibroman

    Canting keel forces

    Possibly... is the keel coming clear of the water when they "launch" ? I havent seen pics or vids of anything like that but I suppose it does happen?
  5. vibroman

    Canting keel forces

    The only way that could happen is through a "beat" frequency. This occurs as the two signals alternately add to each other and then subtract. Based on the data from the video the beat frequency would be 63 Hz I did not see or hear that frequency. but that may be due to the frquency response of...
  6. vibroman

    Canting keel forces

    Good points all. The natural frequency would not change significantly with wave action. However the exciting forces (flutter vortex shedding or what ever you want to call it will) This could cause the structure to vibrate intermittently. Visualize running finger round top of wine glass. It only...
  7. vibroman

    Canting keel forces

    Let's not get ahead of ourselves. The analysis has probably been done by others, but I will do what I can and post it all. lemme know what ya find VM
  8. vibroman

    Canting keel forces

    Check the ABN audio again and right at the end of the clip there is another similar but lower frequency tone. Spectrum show it at 950 Hz. Possibly other RAM? Wish we new if they all "sing" and if they do could get audio..
  9. vibroman

    Canting keel forces

    Agreed but I heard (saw) talk somewhere that the ram failures were fatigue failures. Surely there have not been enough cycles due to wave action etc to cause a fatigue failure? However with 1000 Cylces per second contributing they might get there.
  10. vibroman

    Canting keel forces

    That is pretty close I'll have a look for more video/audio and compare Anyone have details on the hydraulic pumps ? RPM, number of vanes/pistons?
  11. vibroman

    Canting keel forces

    OK so having analysed audio from the ABN AMRO video the singing frequency is +/- 1011 Hz (cycles per second) or 60660 Cycles per minute. Thats a pretty high frequency and if it is resonance then the structure resonating must be very stiff. Possibly like a keel support structure or ram ?? Now If...
  12. vibroman

    Canting keel forces

  13. vibroman

    Canting keel forces

    I've got / can get the tools is there a link to the vids/audio that have the hum anywhere ?
  14. vibroman

    Canting keel forces

    Without data its tough... but without the magnification factor of a resonant condition I doubt the forces from cavitation or vortex shedding would be enough to make a large structure like that vibrate enough to be discernible. The cavitation / vortexes triggering a resonant response is more...
  15. vibroman

    Canting keel forces

    It would be real easy to prove/disprove keel resonance as the issue. We have a frequency of the "vibration" while the boat is moving...Run the audio track with the humming noise through a spectrum analyzer. Then it would be necessary to perform impact testing on the keel and other various...
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