[brian eiland]

Originally Posted by YachtForums

NEW TECHNOLOGY...
Aftermarket impeller manufacturers are somewhat limited in what they can develop. Their primary goal is to make impellers that offer better performance than the impeller included with most of the O.E.M.’s, which are now using some form of stainless and or progressive pitch impeller that was chosen to give the best all around performance for a given craft, based on the torque available and the rpm produced by a given powerplant. In most cases, engine modifications will dictate the need for an impeller better matched for the torque and rpm available from said modifications. This will result in increased speed and/or acceleration in most circumstances.

However, current generation jet pump configurations and placements are the real limiting factor. When the leading transportation manufacturers begin incorporating more advanced pump designs, i.e., dual-stage axial flow pumps, surface piercing jet pump drives, variable geometry venturis, vacuum enhanced intake gullets, and some of the other technologies that we pioneered into production vessels, we will begin to see an entirely new era of impeller designs, sizes, materials, applications and results.

A more important area to examine for now, regarding current generation impellers, has not been addressed by any of the manufacturers. Here are some of those areas...

1) The pressure differential between the area located immediately in front of and directly behind the leading edge of every blade at the root. This problem manifests itself in the form of cavitation burns in this area.

2) Controlling hydraulics where the outside edge of the blades meet the inner liner wall. Remember, water is not just forced backwards on a blade, but travels outwards as well. It is the impact of water against the inner liner wall that substantially reduces the over-all efficiency of current single stage axial-flow pumps.

3) “TRUE” Variable Pitch Impellers. This can accomplished via mechanical means and activated by variables in hydrodynamic pressure. Centrifugal force can activate blade rotation and hydrodynamic pressure can control the angle of attack.

Originally Posted by YachtForums

In order to accommodate the mechanism/gears/cams for controlling pitch, the size of the impellor hub must increase in size proportionately. The larger the hub, the greater the obstruction to flow. In an axial flow pump, this can be a problem. This is the main reason a rim-driven prop is a more effective design

Originally Posted by Innomare

One exception is the jet drive, though, where the propeller (actually impeller) is so efficient because it hardly has any blade tip losses. I wonder when, or if they'll come up with an electrically driven rim-drive waterjet propulsion. It seems like the best of both worlds to me. No shaft going into the waterjet…

It certainly appears as though the rim-driven propulsor concept has a lot of potential as a component in a jet pump drive system……ie, a rim driven impeller (“a new era of impeller design” as noted by YachtForums). Now we know there is considerable work being done on rim-drive technology, particularly those incorporating permanent-magnet electric motor components to power-up the rim. These electrical driven rim-drives may prove too advanced, overly complicated, and/or too expensive for small PWC or RIB jet applications.

So what if we look back at mechanically driven units. I would imagine it would not be too difficult to design up a kevlar-belt driven unit similar to either of those depicted at Peripheral Journal Propeller Drive utilizing suitable bearings and minimal water seals as the whole ‘rim cylinder’ and belt-drive mechanism might be contained in a ‘water box’ as noted in AIR Fertigung product info.pdf. The input drive shaft would exit the ‘water box’ to be hooked up to whatever motor was chosen to drive the jet pump unit. The water seal incorporated at the drive shaft’s exit point would guarantee the ultimate water integrity of the boat in case of failure or slow leak of a seal at the rim itself. And the water box concept would allow for the removal of the whole impeller drive unit for inspection or repair even while the vessel was afloat. Kevlar belt drives are a proven entity as I note at RunningTideYachts/Power.

One variation of the rim-driven impeller itself might consist of a fixed-bladed model where the blades were ‘fixed’ to the inner circumference of the ‘rim cylinder’. Per note:

Originally Posted by YachtForums

Over-lapping blades are one of the most beneficial ingredients in pump efficiency, along with radial edge (swept) blade designs.

So I assume these fixed blades might best appear a bit more elongated or ‘screw like’ to obtain some overlap, maybe??

My next thought went to why not add a progressive pitch to these fixed blades, so that the water was accelerated some additional amount. Refer:

Originally Posted by Ben

Has anyone considered using a screw instead of a blade for accelerating the water? In my mind it could offer more bite with less revs…

Originally Posted by YachtForums

In reality, impellers are essentially a worm (screw) drive, on a shorter scale. There has been substantial research in the area of worm drives, but not for performance. It’s greatest value was in reducing acoustic signatures. A shrouded drive with an expulsion point far aft of a stator section resulted in an unturbulated flow that was hard to detect. But, worm drives are not good accelerators, because you cannot progressively increase the pitch. As the volume between the blades increases, there is no source of fluid to draw from. Unlike a turbine that can compress air via a system of increased blade rpm and pitch, water cannot be compressed… only accelerated. However, it is conceivable to “feed” or draw in water at specific points on the exterior of the worm drive to fill the void. The SR-71 Blackbird used a similar system to draw air into the afterburner, because the amount of air present at higher altitudes was reduced.

The rim-driven impeller may offer some alternatives to this equation that might allow for progressive pitch of the blades. My first thought was that the inner circumference of the rim drive ‘cylinder’ might be constricted in diameter along its length to compensate for the change in volume between the progressively pitched blades. Next I thought, maybe some sort of inner hub attached to the blade tips configured as a cone to account for the volume changes.

But wait a minute, both of those solutions restrict me to only processing the same volume of water that I would with the non-progressive pitched blades. How about making use of that that ‘center channel stream’ of water that would exist in the free space between the inner blade tips of the rim drive impeller? Could this be the source of my extra ‘feed water’ to fill the void crated by the progressive pitch?? This ‘free space’ down the center channel of the rim drive impeller might offer several virtues;
1) provide ‘feed water’ for progressive pitch blades
2) provide extra water to stave off early aeration of the total flow
3) provide a path of less resistance for ‘excessive’ flow that the inlet gullet might have allowed, thus cutting down on resistance to the boat’s forward progress, and making adjustments to the inlet gullet volume less critical.
4) provide for a greater overall water processing capability than a same diameter hub driven impeller jet pump (more water = more thrust)

With respect to the aeration I mention in #2, I reference this quote:

Originally Posted by YachtForums

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. They ventilate, thus inducing air into the equation. Because the amount of water available for compression at higher speeds is reduced, due to the introduction of air, there is less water density available for thrust

Besides the hydrodynamics of the situation, the rim-driven impeller obviously offers a lot less potential for fouling at both its hub-less center and at the zero-gap, blade-to-rimwall area of a jet pump unit.

Those are some thoughts of mine on fixed-pitched blade rim drive impellers at the moment. There may be some arguments for variable-pitch blade impellers, but that complicates matters for the ‘small jet pump units’. (maybe not as much so as in the case with hub driven jet pumps, but more complicated, never the less).

I look forward to the comments

[brian eiland]

BTW, Carl I’m still looking for more discussion on that ‘pliant material’ you’ve mentioned on several occasions

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.

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.

Were those both the same material for the inlet gullet and the venturi? Is it, or are they, both still ‘classified’ ??

[brian eiland]

Just ran across this on-line design process

http://www.marinejet.com/view/53

quoted....
Over the next few weeks NAMJ will show you the entire process of producing a new jet from scratch.

NAMJ will go through the entire research and development process of design, building test models, testing, outcome of testing and then to production.

We will try to post the results as they happen.

Monday (5/15/06) will be the first day of posting.

So keep coming back to the web site to see the progress of the new low horsepower small jet line.

[wdrzal]

I read that too, I was thinking of EAP (electro active polymers) or EPA' s (electroactive polymer acuators) when current is applied they get shorter and fatter. A lot of reasearch is being done because they are promising for artificial muscials in artificial limbs.

NASA has the patent but released a lot of info so more private reasearch can be done.I can't recall the name that program is under right now.



there a movie there it takes awhile to download
http://ndeaa.jpl.nasa.gov/nasa-nde/l...-EAP-books.htm

http://electrochem.cwru.edu/ed/encyc...-elact-pol.htm

If I,m correct that will get you started, if not its a intersting subject.

[brian eiland]

From another forum I ran across this posting that I thought might be interesting to this thread discussion.

Originally Posted by Riverjet502

Gentelmen, When you are talking about preloading an impeller you are referring to an inducer. This does help your hole shot especially when working with a loader in the intake, but doesn't always produce a higher top end. This works very well at reducing cavation. One thing to remember or think about from the above posts is that there were three styles of pumps mentioned above; axle flow, mixed flow, and centrifigul pumps these are not apple to apple comparisons. Each has its own nitch so to say where it works best for the craft it is installed in.

[brian eiland]

Been quite awhile since I revisited this thread, and don't know that I have that much time to pursue it now. But I did happen across another 'pliant material' research;

"Agile new plastics change shape with heat"
Researchers have invented a class of materials so remarkable for their agility in changing shape as they react to heat, they might be described as acrobatic plastics. The new materials, known as "triple-shape materials," can assume three different shapes, each shape depending on how much heat is applied.

http://www.manufacturingcenter.com/dfx/news/stories/feature-2.asp?

[brian eiland]

Redmond, WA September 11, 2007 -- IntelliJet Marine, Inc. has been granted U.S. Patent # 7,241,193 for its Variable Marine Jet propulsion technology. The company believes the IntelliJet™ technology will answer the expressed desire from boaters for greater reliability, more economical operation, and increased maneuverability and safety.

The company is currently testing the IntelliJet™ and preparing to go into production.

The technology incorporates continuously variable power transmission (CVT), now becoming standard in automobiles, and simplifies operations by eliminating the need for reverse gearing or a reversing bucket. "Existing boats utilize a fixed drive system that hasn't been seen in automobiles since the Model T. The IntelliJet™ is naturally expected to enhance fuel economy and engine life in boats, just as transmissions have in automobiles," says Jeff Jordan, President of IntelliJet Marine, Inc.

Management expects the IntelliJet™ system to offer better efficiency than conventional jets and propellers over a wide range of operating speeds and loads.

The technical details are well documented in issued patents, white papers, demo videos, and PowerPoint presentations to industry groups, available at www.iiJet.com.

....previous background
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.

[Highlander]

WOW, What a lot of discussion about jets from many people who have experience with them.
I have run a whisperjet 40 for 8 years and 17,000 NM.
Yes it is not efficient at displacement speeds and requires attention steering when going slow.
But as soon as it gets on plane you get 1 mpg from 20 to 30 kts
Lobster pots slide under without a worry. The boat is smooth and quiet.
No boat (including the new volvo drive) has better manuverability.

[LibertyCall]

Since electric motors make full torgue at all RPMs, wouldn't Diesel-Electric make good sense paired with jets?
Doug Underhill

[Dan Evans]

Diesel electric to waterjets would work, but it would be very heavy. With any diesel electric system you would need the diesel engine, a generator then an electric motor and the waterjet. All of these are very heavy including the waterjet since it is full of water. What I would like to see is a fuel cell coupled to a superconducting electric motor either podded or turning a waterjet. A search on this forum for "fuel cell" will turn up more results than you can expect. Fuel cells; clean, quiet, no moving parts and a good source of fresh water for your yacht! Actually I am not sure about the drinking part, does anyone know if fuel cell exhaust is potable? I don't see why not...

[Garry Hartshorn]

I believe that drinking pure fresh water ( less than 50 ppm ) will cause extreeme diarrhoea.

[Dan Evans]

Okay, so no drinking fuel cell exhaust...
I am very interested in the idea of electric motors, especially superconducting motors, turning waterjets. Are there any thoughts on this?

[BMcF]

Originally Posted by Dan Evans

Okay, so no drinking fuel cell exhaust...
I am very interested in the idea of electric motors, especially superconducting motors, turning waterjets. Are there any thoughts on this?

There certainly is..much more than just thought going on within the USN and ONR on exactly that configuration. A great deal has been spent on developing what has been called the 'AWJ' advanced waterjet, a 35MW motor to drive it, and similar high power density, high-efficiency power generators. It's going to be a while before it all reaches the point where it is mature and then scaled down for application in smaller vessels..such as megayachts... but not that far off.

Interestingly, at the very 'low' end of the power spectrum, there are simliar solutions (similar in terms of motor/generator technology and control..not in size) on the market for electric drive. It will be interesting to see how fast the two solution sets, at opposite ends of the future continuum of solutions from small to large, 'converge' toward each other to meet at sizes that cover the typical megayacht's requirements.

[Marmot]

"I believe that drinking pure fresh water ( less than 50 ppm ) will cause extreeme diarrhoea."

Why would you believe that?

On steamships we make between 10 and 20 thousand gallons a day of the purest distilled water known to man and the high quality distillate that becomes boiler feedwater is the same stuff that fills the potable tanks.

There are thousands of very healthy seafarers who have sailed on high pressure steamships for the past 50 years and suffer no ill effects. We simply do not make two versions of water.

[K1W1]

Hi,

Marmot- At what temp are you making this distillate( I assume you are using a flash evap here) and how differently do you treat what's going into the potable vs whats going into the feed water?