Jet Drive vs. Prop

electro-magnetic propulsor as part of a waterjet propulsion unit

Abstract

A concept investigation has been carried out into the possibility of using a tip driven electro-magnetic propulsor as part of a waterjet propulsion unit. The primary advantage is that there is no need to insert a drive shaft within the waterjet inflow. This significantly reduces cyclic variations in the propulsor inflow and removes an area of flow separation around the shaft. It also provides the designer with greater freedom as to the types of propulsion systems available and where they can be placed within the ship.

The viability of the concept has been examined by considering the performance of an axial flow electromagnetic thruster developed for the ROV market and numerically studying its performance within a typical waterjet inflow. A study was also conducted to examine the scalability of such propulsion units. It is concluded that for a typical size of waterjet with an input power requirement of 110 kW and diameter of 0.25m the maximum delivered power at 2,200 rpm would be 90 kW. This design would have the benefits of no shaft induced losses and reduced cyclic blade loadings and should deliver a higher thrust than comparable conventional waterjet units using geared electric motor drives
http://eprints.soton.ac.uk/22746/

Electric PWC, the Green Samba

Got a note from a fellow just today asking if I had seen this... I had not.

It's not the first to try its hand at an all-electric personal watercraft, but the Ohio-based Silveira Group is claiming that its new so-called Green Samba will be the first "viable" vehicle of its kind. To that end, the company says that the Green Samba will deliver the same 65 mph performance of the fastest 260 bhp sit-down PWCs, and do so while remaining completely silent thanks to a pair of twin direct drive electric propulsion pods. As the company is quick to point out, that also has the added benefit of eliminating one of the biggest complaints about PWCs from the public: their noise. Of course, the other key to viability is the price, and Silveira is unfortunately doing decidedly less talking about that right now, saying only that it will be able to "ballpark a retail price" when it finishes work on the latest prototype in August.......Gizmag

Wonder what the details are on the propulsion unit(s) ??

Unique Propulsion Unit(s)

...just found this:

When we wrote up the Samba in April 2009, it had already been through four prototypes, and several more have seen the water since then. The latest iteration has seen the shape and construction refined to such an extent that according to Rodrigo Silveira, just 65 bhp is now required to match the performance of the biggest 240-260 bhp Sea-Doo, Kawasaki and Yamaha designs. But the aim had also been to eventually replace the 800cc twin-cylinder internal combustion engines the company was using in the development process with electric propulsion.

In the last twelve months, the company almost gave up on that process. "I can tell you that making a green watercraft is not easy," Silveira told Gizmag.

"Our experiments were becoming more discouraging. We knew that the public would not accept lesser performance to go green – being a good citizen does not compensate for being ten mph slower than your friends on their internal combustion skis."

"We wanted to use an electric motor but the amount of energy required to get a jet ski on the plane was so large that it was using too much of the battery capacity. Combustion engines give you the torque you need to get to planing very quickly, without using too much of the available stored energy. We refined everything we could but to get the engine performance we wanted, and sufficient range, we would have needed 150 pounds of batteries which would have impinged on the weight and hence maneuverability too much. We had some sleepless nights wondering if our objectives were achievable with the current state of battery technology."

As the man who split the atom is oft quoted, "we didn't have any money, so we had to think" and it was in going back to the objective and rethinking it that the breakthrough came for Rodrigo. With limited resources and the high burn-rate of funds associated with intensive R&D, Silveira acknowledges that he was on the verge of giving up when the breakthrough came.

"We realized that we had been focusing on the motor, not the pump. In the same way that automotive electric propulsion is just about to go through a revolution of design because it doesn't require the same centrally located ICE we have had for the last 100 years, we began exploring what could be achieved with different propulsion methods."

"Once we began looking, we came across a propulsion technology originally developed for military applications that had not been previously used in watercraft and we have now acquired an exclusive license for using the technology on watercraft. After testing, we are now confident it makes our objectives possible both weight and price wise."

"With twin electric shaft-less drives of far less modest horsepower output, we are expecting about the same top speed as with the 65 bhp gas engine, which will give us 65 mph. In some ways the US Coast Guard's limit of 65 mph for watercraft has worked to our advantage as otherwise we'd probably be seeing 80 mph watercraft by now. Aiming at a non-moving target of 65 mph has been a huge advantage."

"The PWC is a huge water pump and the existing manufacturers have ignored the inefficiencies of the jet drive system currently in use by pouring horsepower and fuel on it. The inefficiencies in the horsepower-thrust conversion are quite obscene and that's were we've been focusing our energy."

"The propulsion pods we're using have an electric motor self contained within them. Each one has one moving part on the internal wall of the thrust pod, so it's a direct drive and it has eliminated many of the losses and made the system extremely efficient. What started out as a 6 horsepower motor became two 12 horsepower pods that are far more efficient."

"Our tank tests have proven to us that we can achieve between 34.9 and 36.5 pounds of thrust per horsepower compared to 28 pounds of thrust from a gasoline engine. By going electric and having a self contained pod that isn't connected to anything else other than a power source and a controller, we have achieved a similar freedom of design as automotive designers are now experiencing with electric motors. It means we don't need a big fat motor and a drive train in line with the motor."

"We started out with a single, centrally-located propulsion unit, but along the way, we realized if we made it into a dual pod system we would gain maneuverability by being able to get far more angle on the thrust pods than by using the traditional centrally-located nozzle steering. Then to take full advantage of turning the propulsion units, we had to completely different hull configuration."

"The redesign allowed us to put the pods below the planing line, which allows a more efficient intake and even better performance. With traditional design you can overload the pump, so you have a limitation on the amount of water going into the intake tunnel, but with these pumps we realized that the more we feed the pump, the better the performance.”

One of the benefits from using a lightweight, low-powered craft with such efficient drives is that the range of the unit has now skyrocketed and Rodrigo expects to get more than three hours usage from a full charge – well in excess of the 250 horsepower sit-down PWCs.

"Our testing so far shows that by getting the two pods on either side of the center line, you can get amazing turning ability. The first tests showed it was a bit too sensitive – it'd tip you off too easily because you just couldn't hold on. The prototype we have planned for August brings all the strengths into focus and… we're confident now we have a viable next generation PWC in every respect.."

http://www.gizmag.com/green-samba-first-viable-electric-pwc/15141/

...and some more pics
http://www.gizmag.com/green-samba-first-viable-electric-pwc/15141/picture/114776/

ahh, such an optimist you are

I was thinking it sounded more like these two subjects I brought up before:

Posting #31, Rim-Driven Impeller

Posting #47, Electro-Magnetic Propulsor as Part of a Waterjet Propulsion Unit

Links to Rim-Drive Propulsion Thread

Over in this subject thread on rim-drive propellers, have a look at postings #12 and #13

http://www.yachtforums.com/forums/technical-discussion/3961-rim-driven-propellers.html

Rim Drive Impeller OR Intregal Canned Electric Motor ??

Opps, I might have been too quick to suggest this new jet unit was making use of a rim drive impeller.

What if it is of a form of an 'intregal canned electric motor'?
http://v3.espacenet.com/publicationDetails/biblio?CC=CA&NR=2137607&KC=&FT=E