Ringed propeller; if it looks like a duct and quacks like a duct

Simple is better… most of the time. My thoughts of the simplest; yet safe; thruster for an e-foil are 1) direct drive and 2) an optimized ringed propeller.

Some kind of duct or shroud is needed for safety. A well designed duct can increase static thrust but adds drag at speed. A simple safety shroud only adds drag. The drag is not just due to the ring portion of the shroud or duct, but drag is also created by the support struts.

The idea with a direct drive ringed propeller is to simplify the thruster, and also to minimize wetted surface area and drag at speed.

An optimized ringed propeller would probably have blades with a relatively small tip
cord…this allows a minimal safety ring.

The pros for the direct drive ringed propeller are:

  1. smaller diameter prop for direct drive (probably) = smaller ring, less wetted surface area
  2. much less wetted surface are than shrouded/ducted propeller, less drag whie at speed.
  3. cheaper and simpler implementation

The cons for the ringed propeller are:

  1. greater energy losses, more energy spent spinning water
  2. less prop guarding, but probably adequate

My gut feeling is the net effect on efficiency will make a well designed, direct drive, ringed propeller comparable to a ducted propeller while operating at higher speeds.

Looking forward to other’s thoughts on this.

ringed propeller with small tips and minimal ring, sorry about the poor sketch.

Yes, i posted this for 1 or 2 days ago.Hope someone vil pic it up.
Flex2d Peter
Hi Peter, like your build, i am from norway, my engles is bad, sorry. I was thinking about your prop. My idea is to put a ring on the prop. Not a duct.This has several benefits. I can absolutly nothing about props, but i read that alu prop has bigger “slip” because it is soft, 2 cavitasjon,3 some safty less than fix duct more than nothing, less parts. Maybe more. Anyway just some ideas, Please tell me what i am missig, i am learning. Love your work. se the picture.
Regards Aslak

imageimage.jpg800x600 153 KB


Some pic i find on in.image

Flex, yes the same idea you shared. The ringged prop will need to be optimized for e-foiling.

My prediction for the future of e-foil thrusters:

  1. Direct drive, inrunner potted, designed to run wet including bearings; no sealing problems, better cooling.
  2. Ringged propeller
  3. No motor enclosure

Winging it, agree, i have too thought about 2. and 3. No.1 I have not, is over my head, but i like direkt drive and as few parts posible. Two minds…hope there vil be several. This is fun:)
I just read this, very interesting, safty, cavitasjon,cost, speed, drag…
Pls read:

Sorry for my bad english, keep up the good work.:sweat_smile: Flex.

I’d like to test this idea in the near future. I’ll test in a tank and share results. I would need help from someone with fluid dynamic/propeller designing skills and also someone with cad skills to create a printable file. Any takers?

So far the best inrunner I can find is the SSS 360kV similar to the motor that pacificmeister is using. I’ve been searching for a similar but larger diameter inrunner, but no success so far.

My thoughts on the direct drive ringed prop design:

  1. Bullet hub to match motor diiameter.
  2. 2 piece hub to form a collet for easy attaching to the motor shaft, collet bolt at the pointy end of the hub to allow clamping of the collet.
  3. Airfoil cross section hoop.
  4. Optimized pitch and diameter for direct drive.

I’d also like to test this set up with the motor flooded and unflooded for comparison.

1 Like

@Flex @Winging_it

Any news on that front?
I was thinking ring propeller to … simpler than a duct and safer than open propeller.
And… it could fit around an out runner.

I haven’t tried this yet. My biggest concern is how much centrifugal pumping, and subsequent pumping losses would result from the spinning ring.

It also increases inertia and as there is more rotating mass at the max diameter, it needs to be well balanced.