Thread: more speed
01-06-2007, 12:48 PM #1
During acceleration, from idle to just after planing, you want to maximize
water flow, or fully load the pump. The greater the volume, the greater
the thrust. From midrange to top end, contrary to what you may believe,
the opposite is somewhat true. To achieve the greatest rpm's and top end
speed, you must reduce some of the volume the impeller receives. This
system works similarly to a surface piercing outdrive found on high
performance offshore race boats. At low speeds the outdrive is trimmed
down placing the entire prop beneath the hull line. This allows the
greatest amount of torque to be transferred to the prop, thus maximizing
acceleration. At operating and top end speed, the outdrive is trimmed up
to bring a portion of the propeller out of
the water, which in turn allows the prop to turn at higher rpm's without
the drag incurred of a fully submersed prop.
For example, when you're running at mid to top speed, on smooth water
conditions, in a straight line, with a stock or open grate, have you ever
had a cavitation problem? Of course not!!! Did you know that water is only
through the lower impeller housing? It's true!! Pumps do not run fully
loaded at high speed. It's physically impossible for water to divert to
the top of the impeller housing at 50 mph plus. Well, the same holds true
for rough water operation. It is not necessary to load the top of the
impeller housing as some designs do. This creates drag, reduces rpm's, and
thus decreases top end speed. Remember, water wants to flow a path of
least resistance, varying as little as possible from its course. All that
is needed is to enhance the dynamics that are already inherent within the
At the U.S. Navy's Large Cavitation Channel in Memphis, there exists a
flow track that was developed to analyze lift and drag on various hull
designs. This facility can accelerate water while holding a hull
stationary, duplicate the negative pressure zone at an intake housing, and
by use of flow inks, visually inspect laminar flow from below the surface.
Many designs that are prevalent today can give off a fair amount of
At the U.S. Navy's Flow Dynamics Research Center, a CRAY 9000 Super
Computer is used to aid in the development of some very advanced programs.
Specifically, it was used to analyize data on pioneering work in the areas
of Dual-Stage Axial Flow Pumps, Intake Gullet Enlargement / Reduction
Systems, Variable Geometry Venturi's, Surface Piercing Jet Pump Drives,
Duo-Delta Conical Hull Designs, Deployable Hydrofoils & Pumps, and a
variety of lifting bodies. Most of this work was geared toward a protocol
set forth by the Department of Defense for small waterborne tactical
assault vessel for the Navy Seal's. Very much like current generation
watercraft except much, much faster!
Given the parameters of today's personal watercraft configurations, i.e.,
weight, displacement, speed, thrust, and volume, it is possible to achieve
a design with little or no induced drag, and the same pump priming
capabilities that popular "scoops or loaders" possess, without the loss in
top end speed that some units can suffer from. Ironically, top loaders,
which were designed
for jet boats of the mid 1970's are not really the "hot set-up" for
personal watercraft. Here's an example: If you measure a traditional
Jacuzzi, Dominator, Berkeley or American Turbine intake gullet, you would
the length or "footprint" of the gullet is 22-26 inches long. With a top
loader installed, the leading edge of the scoop is about half-way back
from the upsweep of the intake gullet, this leaves another 12 inches after
edge of the scoop for water to turn up to the lower impeller housing. Top
loading works in this scenario because there exists ample room for water
to divert to the upper & lower impeller housing. HOWEVER, PERSONAL
WATERCRAFT INTAKE HOUSINGS DO NOT FUNCTION LIKE TRADITIONAL JET BOATS!
Watercraft work more like surface piercing drives, in that they are only
skimming across the top of the water. If you inspect the intake area of
your watercraft you will note that the length of the gullet is around 12
inches long. With a top-loader installed, there is only 6 inches left past
the leading edge of the scoop in which for water to turn up to the lower
impeller housing. At 50-60 mph, water simply cannot divert this rapidly
and a laminar seperation is created, resulting in turbulence and
The MAGNA-FLOW utilizes airfoils or "diverters" to help channel water to
the lower impeller housing. These diverters act very much like "stators",
which are directing vanes located just aft of your impeller within the jet
pump. An airfoil (a hydrofoil when beneath the surface) can produce
positive or negative pressure (lift) with a much smaller drag penalty than
a scoop. With proper diversion, the impeller can make the most use of the
incoming water. Too much water and you will overload the impeller and
reduce rpm's. Not enough water and cavitation results. The proper amount
of water entering the impeller will allow it to spread the flow evenly,
thus priming the venturi and maintaining the ideal amount of bowl
Under acceleration, when your hull is beginning to plane and you have not
fully developed lift (bow high attitude ) the airfoils or "diverters" are
at a zero degree angle of attack, creating an unobstructive path of flow
to the impeller while helping to produce lift coming on plane. As lift
develops, and your hull is waterborne and level, the diverters set angle
now begins to act as an enhancement to the natural and drawn course of the
water flow. By utilizing two diverters in tandem staggered placement, it
is possible for the first one (primary) to "preload" the secondary, thus
intensifying the density of flow the impeller receives. This allows a
positive water flow to both diverters and ensures complete saturation of
the lower impeller housing, where water wants to flow naturally.
The real advantage to airfoils is that water can be turned upwards without
incurring the high pressure zones (or drag) normally associated with the
shape of a scoop. As water turns upward with a scoop it creates higher
pressure until the water is released from the scoop and travels back into
the impeller. With diverters, water is turned upwards but is released of
pressure as it begins traveling over the airfoil towards the trailing
edge. At higher operating speeds, the diverters create more down force,
becoming more pronounced when encountering lift, such as that felt when
launching off waves. This aids in keeping the hull down on the water,
therefore helping to keep the pump primed. The resulting action reduces
cavitation tremendously and allows much greater speeds and acceleration in
rough water operation, with near zero loss in speed on smooth water.
Besides the performance gains, several other aspects of this design
contribute to overall handling and reliability. Deep side rails that hold
the diverters create leverage and grip during cornering, while deflecting
water to the pump (the rails convert any side slippage into deflection).
The rails also aid in straight line tracking and the depth of the rails
allow a recessed placement of the diverters should you run over any
objects. This placement also creates a grid, which aids in keeping foreign
objects out of the impeller housing while allowing water to pass freely.
This design is relatively free of molding fillets, thus minimizing frontal
area and parasitic drag.
Carl Camper, President
ULTRAC PERFORMANCE SYSTEMS
1500 N.W. 62nd Street, #510
Ft. Lauderdale, FL 33309
954-351-1943 / 1944 fax
Reply 136c/5ec974ce9d8b34d9?lnk=st&q=jet+boat+impeller+pitch+ &rnum=3&hl=en#5ec974ce9d8b34d9
Last edited by WATER WOODY; 01-06-2007 at 12:52 PM.
01-06-2007, 03:31 PM #2
01-06-2007, 04:03 PM #3
01-06-2007, 06:34 PM #4
there is more speed on the table folks!
01-06-2007, 06:35 PM #5
01-06-2007, 07:07 PM #6
Ive been studying these pumps for a while now and i have learned a great deal about them.I have some great ideas to improve them.
01-06-2007, 07:48 PM #7
- Join Date
- Aug 2006
woody,get the sheepstains off your intake also theres a velcro glove in the nozzle .there will be more speed found every year thanks for thinking out of box . now if there could ba a adjustable intake grate
01-06-2007, 08:03 PM #8
Nice post Wood!
I gotta reread it about 4 times.
01-06-2007, 08:27 PM #9
- Join Date
- Jul 2006
I've read it twice now and still pondering and letting it soak in. Lots of info there. I do wish the ULTRAC PERFORMANCE SYSTEMS site was up. I want to see more now. Good job wood.
01-06-2007, 08:33 PM #10
he he......... i hear something.........shhhhhhhhhhhh...! OH...thats the sound of more speed! Wood Dawg in da hayouse!
Last edited by WATER WOODY; 01-06-2007 at 08:36 PM.
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