[Kyfho]

These rim thrusters are already in a size and power for integration into mainstream yachting circles. Canyon ROV utilise these on their Schilling Quest electric work class ROV. Alstrom bankrolled the development with their eye on future markets. There were initial teething issues, mainly to do with material/lubrication of the ring bearing and adjacent surfaces, and these have been resolved. Cost is the prohibiting factor at present for the general public. Now that the idea is out there and proven, development by competitors is sure to reduce the cost to a more attainable level.
Regards,
C.

[YachtForums]

Came across a video of a rim-prop thruster being tested...

http://www.compositecarbonfiberprop.com/ring_prop.htm

[brian eiland]

Haven't heard much on this subject in quite some time, so I thought I might look thru the internet to see what might be found.

Found this PDF, Design of an Integrated 100kW Permanent Magnet Synchronous Machine in a Prototype Thruster for Ship
"An alternative solution is a rim driven thruster where the shaft and gear has been removed. There are only propeller blades in the water path and only electric cables go through the hull. This improves the efficiency of the propeller, removes the gear and reduces vibration. In this paper the design of an integrated electric machine is presented together with results from the testing of the electric machine. Bearings, hydrodynamics and noise are not discussed"

http://www.elkraft.ntnu.no/eno/Paper...vli-Sandoy.pdf

Can anyone add anything new?

[brian eiland]

Extracted this view of a rim drive unit from a document recently sent to me

[Kruse]

I see a lot of potential in these systems:
- The large diameter of the motor will produce a lot of torque.
- Potential for max efficiency with the direct drive (no gearing or gearbox).
- Minimal profile in water, the benefit of ducting (efficiency and build-in rudder function).
- The rim-mounting of the blades (no center hub) should make them much less sensitive to damage.
With somewhat flexible blades (less pressure on the blades in the center),
they could survive chewing on fishing nets, logs, big fish, terrorist divers and pirates etc.

The big question now is longevity, effectiveness, availability, and prize.

Any risk of a galvanic corrosion problem on metal ships with the Carbon/plastic?

[brian eiland]

Abstract

Rim driven thrusters with structurally integrated brushless PM motors are now an established technology with an increasing range of applications. In these thrusters, the stator of the motor is housed within the thruster duct, and the rotor forms a ring around the tips of the propeller. Such high pole number motors tend to be very thin radialy, have very small length to diameter ratios, and have relatively large airgaps to accommodate corrosion protection layers on the surfaces of the rotor and stator. The relatively large diameter stator laminations of such machines tend therefore to have very thin back of core and narrow teeth, which make them expensive and difficult to manufacture. This paper proposes an alternative potentially lower cost motor topology featuring a slotless stator whose laminations are manufactured from a single strip of steel that is edge wound into a spiral (like a “slinky” and then fitted over the windings that are preformed on the outside surface of a non-conducting former. The former is also part of the sealed housing that protects the stator from corrosion in seawater. The paper discusses the design optimisation of such a motor using analytical and finite element analysis (FEA), describes a demonstrator motor and reports experimental and FEA results.

(had trouble posting rest of article with small file size allowed...will try later to decrease size of file)

[Codger]

Perhaps someone can clear up a question that keeps coming back for me.
Perimeter driven props being more efficient makes perfect sense to me.
However, having sharp ended blades unconnected in the centre has me scratching my head. Wouldn't there be more flex and therefore loss of efficiency as the blades deformed forwards under load? Wouldn't having them connected in the centre make for one solid structure less prone to flex and fatigue?

[First Pericles]

Exchangeable blades. See Brian's post #19.

First Pericles

[Codger]

The blades shown in post #15 are connected at the centre so it's being done both ways.
Replaceable blades is a nice feature but is there a tradeoff in overall efficiency by not having them connected at the centre?

[Castlerock]

I think that having the added strength of the center hub would reduse blade flex and pitch change. Then again if you could calculate the load and flex you could design in more pitch. Now if someone would make a composite Pod Drive with this system for yachts I can see it being much lighter that the Schottel and ABB units.

[brian eiland]

Rolls Royce has posted a few new PDF documents

http://www.rolls-royce.com/marine/do..._rimdriven.pdf
http://www.rolls-royce.com/marine/do.../prop_broc.pdf

[Highlander]

The first thing that popped out is that the blade design can use much less material- less drag. The point of highest velocity/load is at the rim where support is best. The last picture shows a plug connecting the blades- vibration control?

The bearings are interesting too. By using water to generate a hydrodynamic film-the wear component can be less in steady state operation than in start-stop service like a thruster.

The only drawback is the drag caused by the tube/motor.
For commercial displacement use this has lots of promise.
How do you think the drag compares to the IPS design?

Carl

[Dan Evans]

I hope I am not getting too sidetracked here, but has anyone looked at putting these in a waterjet? I know that installing a waterjet with a rim drive means that the rim drive is now inside the hull so if it leaks its going to be a bad day... The drive is already in a tunnel so I dont see why it wouldnt be easy to adapt to a jet. I think it is a great idea not having a shaft turning in the water but I dont think it is a good idea to have the rim drive mounted under the hull. It is an expensive and probably sensitive piece of equipment.

Dan

[Highlander]

Sure it could work and work well.
The downside is that every major component is the most expensive way.
1- jet housing
2- rim drive pod, could be removable from the jet housing for service.
3- Variable frequency drive.

All this stuff works great and has an unknown service life in a marine environment.

Carl

[Dan Evans]

Originally Posted by Highlander

The downside is that every major component is the most expensive way.

...seems to be a common factor in this industry