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1010Re: Home Page Pix

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  • Jean-Yves Renaud
    Aug 4, 2007

      No Pete, we are not all sleeping. See hereafter a cut and paste of today's report about the

      Experimental proof (one more !) of the dissymmetry of a propulsion by reciprocating waterjet.


      Purpose of the experiment: to show that sucking water on the bow of a ship has a negligible impact; though a jet backward propels.


      Principle of the foresee assembly:

      A symmetrical hull (according to transverse and longitudinal axis) to avoid endless discussions.

      Electric pump located in the middle of a pipe of ID « d ».

      Internal diameter of the cross-over equal to more than 2xd.

      Thus, on one hand the pressure drops upstream and downstream will be nearly unchanged. And on the other hand, the speeds inside the cross-over will be very low and the resulting forces being opposed they will cancel each other.


      Measurement of the boat velocity in both cases: sucking and delivering.


      Practical results:

      Measurement of the boat velocity when propelled by jet. Result: 72mm/s.

      Measurement of the boat velocity during sucking. Result not measurable. Velocity lower than 1mm/min.

      Knowing that the thrust evolves as the square of the velocity, one can calculate the ratio between pushing and pulling forces. The pulling force (when sucking) is roughly 20 millions times weaker than the pushing one.


      Conclusion : this experiment confirms the theory. Sucking ahead has a negligible effect, and the related assumptions used in other documents are justified.

      For more details see www.eclecticspace.net .  ...when Loïc have found the time to do the job. 

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