[brian eiland]

....guess I will have to continue this discussion in this new posting...

Originally Posted by YachtForums

On the subject of intake gullets, which are only one aspect of jet-pump integration and configuration, I should expand on the venturi...

Of all the components that make up a jet pump, the venturi is by far the most critical component in dimension, shape and size. It is the final stage of acceleration that water will receive prior to expulsion. The venturi, for those of you not familiar, is the shroud located just after the stator blades (directing vanes) and the part of the jet pump that the steering nozzle or thrust deflectors are most commonly connected to.

The exiting size of the venturi's orifice is generally half the size of the dimensional area of the intake gullet footprint, or a 2-to-1 reduction. Quite simply, the venturi is a reducer or compressor, and in the case of water, which can not be compressed, it is an accelerator. The venturi is one of the most important links or stages in jet pump design. Without it, the jet pump as we know it... would be rendered benign.

Increasing the venturi's expulsion size will decrease backpressure, and allow water to be processed more rapidly, thus moving the hull (mass) forward at a faster rate due to more available thrust, but sacrifices top speed because of reduced compression. Decreasing the venturi's expulsion size will create more backpressure, which results in less water being processed, but increases the velocity at which it exits. This results in higher speeds, but does not give the mass of water necessary for greater acceleration. Venturi designs are usually a compromise to give maximum acceleration and top speed.

The real reason that an adjustable venturi is necessary and holds so much value is that because pumps do not run fully loaded at higher speeds.

As I said before it does appear that the real secret to increasing jet-pump efficiency is to incorporate a varible inlet and outlet.

Originally Posted by YachtForums

In early 1984, our research team began conceptualizing and theorizing the potential of an adjustable venturi and later developed the V.G.V. (variable geometry venturi) This unit operated on the principles mentioned above but utilized hydraulics to control orifice diameter, which was necessary given the huge amounts of thrust created on the research vehicles we developed. In 1987, a very unique material was made available, current regulated (electrical stimuli), that lined the inner walls of a venturi (or bowl) and controlled exact camber and orifice dimension. This material has future applications i.e., artificial limbs, robotics, etc. Unfortunately, it is under regulation for now and there is no access to it.......
Inner wall flex and fluctuation is critical as well. The reason that I mention flex is because it is conceivable to utilize a material with built in flex to accomplish some desirable characteristics.

Here is the mention of that 'pliant material' again.

Is this material still so classified as to not be available in the commerical market??

Since it was a pliant type of material, was there some upper range of HorsePower that might limit the utilization of this particular material??

Originally Posted by YachtForums

One of our first VGV’s was an adjustable venturi that utilized inner bowl “feathers” actuated by an aperture that closes concentrically. While it was mechanically a very cool-looking contraption, much like the afterburning tail-feathers on a fighter jet, it was hydrodynamically incorrect. The reason is simple, while it reduced orifice size it also increased the rate of compression while failing to control trajectory. Properly configured and controlled, the device had great merit

Originally Posted by YachtForums

A properly designed venturi can yield significant acceleration gains and top speed gains. A really good design will become exponentially more efficient with speed. In other words, the faster you go.. the more efficient it becomes! Venturis work on thrust and pressure. Wherever you have thrust you have the potential to create vacuum. Wherever you have pressure, you have energy. And in the case of venturis, that pressure can control a multitude of variables… and this entire process can be executed with NO MOVING PARTS!

Here again is that "no moving parts" quote that caught my eye on two occassions. I have not had time to look at IntelliJET's patents yet, but I suspect they are an electro-mechanical device to control these orfices...usually complicated, and not all that dependable. I really want to know more about these pliant solutions, if possible??