[brian eiland]

Originally Posted by orion

Has anyone experience of this jet system? www.marinejettech.com

I thought it might be worthwhile to post some text portions of their website here since they are relatively brief, and too often in the past I have had occasion to try and link to a website for more info on the subject matter only to find it no longer available for one reason or another.
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…from www.marinejettech.com

Existing jet boats have the identical problem as the first generation of jet airplanes. Although they are fast and maneuverable, their initial acceleration is so poor they can barely pull water-skiers out of the water. They can be designed to either go fast with poor acceleration, or to provide acceleration at the trade-off of low top speed.

If it were not for these operating range restrictions virtually all boats would be water-jet powered. Jets are safer than outdrives (no prop in the water). They are mechanically simpler than outdrives. They are more maneuverable than outdrives because the jet outlet is directionally controlled. But, historically, the jet was sized for speed and lacked the low speed thrust required for docking and acceleration.

IntelliJet Marine answers these needs. And the result is just as revolutionary as it was in turbo-jet airplanes. Their innovative technologies improve jet performance by up to 80% at low boat speeds, while also increasing top speed, fuel efficiency and cruising range. These patented methods mark the most significant advance in marine propulsion systems in many years.

The intelligent inlet duct adjusts to recover the velocity head of the incoming water at all planing speeds and at all throttle positions. This higher inlet efficiency is most important in designs based on larger jets. Larger jets, in turn, are desirable because they produce more thrust at low boat speeds. This parallels engine development in commercial aircraft where high-bypass turbofans move more air through a larger jet for shorter takeoffs.

This combination of larger jet size, efficient inlet duct, and variable nozzle allows a 50 to 80% increase in low speed thrust, while increasing top speed and maintaining higher propulsion efficiency at all boat speeds and accelerations. These three innovations work together to approach the limits of propulsion efficiency.

Larger Jet Size
increases propulsion efficiency using technology demonstrated in development of larger jets in aerospace industry.

Intelligent Inlet Duct
automatically adjusts to recover the power of the incoming water at all planing speeds and at all throttle positions

Variable Rectangular Steering Nozzle
allows simultaneous control of nozzle area and steering direction to maintain peak efficiency over wide ranges of boat speed, pump shaft speed and steering vectors.

Why It All Works Together
Bigger jets are desirable because they create higher thrust. But the bigger the jet, the more power that is lost in the ordinary inlet duct. This power loss has to be made up by the motor and the pump.

The adjustable inlet duct reduces this power loss. And, as the inlet duct becomes more efficient, it increases pressure on the nozzle, which results in higher flow through the system.

But, higher flow through the system results in reduced pump efficiency. Hence the need for the variable nozzle to regulate the system flow for pump efficiency.

Summary: Using the combination of these three innovations means a high volume of water, an efficient inlet duct and an efficient pump operation under all operating conditions.

The Patents

To view the patents, go to: http://www.uspto.gov/patft/index.html

Click on Patent Number Search.

Enter a patent number noted below.

#5,658,176 “Marine Jet Propulsion System”

#5,679,035 “Marine Jet Propulsion Nozzle
and Method”

#5,683,276 “Marine Jet Propulsion Inlet
Duct and Method”

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So next I went looking for more info on this ‘adjustable inlet and outlet’ subject as related to waterjet propulsion, and found some very nice discussions right here on this forum, and by our webmaster Carl. He begins with some jet-pump fundamentals http://www.yachtforums.com/forums/13462-post27.html
……some excerpts…

Originally Posted by YachtForums

Impellers (and jet-pumps) work on the principal of positive and negative pressure, or a push/pull concept. As a blade rotates, it pushes water back (and outwards due to centrifugal and accelerated force). At the same time, water must rush in to fill the space left behind the blade. This results in a pressure differential between the two sides of the blade: a positive pressure, or pushing effect on the blade face and a negative pressure, or pulling effect, on the backside of the blade. This action occurs on all the blades around the full circle of rotation.

Thrust is created by water being drawn into the impeller and accelerated out the back. To further enhance velocity, water passes through the venturi before finally exiting the pump as thrust. The venturi works on the principle that a restriction or reduction in line size will cause water to accelerate if the same volume is to be realized at the other end of the restriction. This is where you get the "jet" in pumps. Finally, a steering nozzle is used to vector or deflect thrust for yaw direction.

Impeller design and efficiency is strongly linked to the other components that make up the jet-pump, i.e., the intake gullet, its volumetric area, the laminar transition of the intake housing, stator blade area (including angle of trajectory), venturi rate of compression, venturi "bowl" area, exiting orifice dimension, mass and weight of the hull, and pump placement or depth within the same.

The intake gullet is the recessed area within the hull leading up to the entrance of the jet pump. This area plays a vital role in jet pump efficiency. There are a multitude of factors that determine its length, size, shape and depth. For instance, a larger vessel with greater displacement may choose an intake gullet design with a more gradual rake leading up to the jet pump entrance. This maximizes the amount of water available for acceleration. In this scenario, intake gullet vacuum is not as critical because the weight of the hull (and the depth of the pump) will keep the intake cavity primed. In contrast, a light, high speed hull that rides closer to the water's surface, may use an intake gullet with a more aggressive rake and a reduced intake gullet area. This decrease in cavity size, increases the vacuum (or negative pressure zone) at the intake, which helps reduce ventilation brought on by a higher speed planing hulls that operate near the water's surface.

Ultimately, the best intake gullet design would be variable in size. In other words... larger for acceleration and smaller for high speed operation, to maximize intake vacuum when aeration is present.

Originally Posted by tantetruus

Do varible gullets exist??

Originally Posted by YachtForums

Not really, although it is possible to mechanically reduce the volumetric area of the cavity without having having an adverse effect on laminar flow. I've done a considerable amount of analysis in this area and it yields great improvements in efficiency, but the mechanical means of altering the gullet would not prove economically viable.

Originally Posted by Codger

There was a variable intake for waterjets in development during the mid 90s. All that I saw of it was a paper-napkin drawing during a conversation that I probably shouldn't have been having. Looked like a NACA duct with a flush spring loaded slider. As speed increased the plate moved aft and reduced the opening size. There was a drag vane inside the throat that was part of the actuator mechanism. Sorry, that's all that I recall about it.

Originally Posted by YachtForums

Yes, I'm familiar with the system. In the end, we developed an inner liner that was positioned on the top of the gullet (and only the top). It used a soft durameter plastic that was flexible enough to pull away from its seated housing as vacuum increased, creating a bubble shape. Because pumps run fully loaded at idle to medium speeds, the pressure of the water kept the "skin" pressed firmly into its housing.

As speed increases sufficiently, water can not make the abrupt turn into the intake gullet as quickly as it can at slower speeds. The result is, a negative pressure air pocket is formed on the top of the intake cavity. This negative pressure zone pulled the skin away from its seated position, thus reducing the volumetric area of the intake cavity, which ultimately increases vacuum and therefore efficiency at higher speeds. The beauty of the system was... no moving parts.

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.

Brian observes: Now this is getting real interesting. We certainly have agreement from all parties that a variable inlet and outlet can remarkable improve the jet-pump performance!!

I must leave this posting unfinished for a few hours while I do something else.