Toroidal propellers

[Thrutch]

I've been seeing these toroidal propellers pop up all over the place over the past few months. Seems like they would be amazing for dpvs. Anyone know if any brands are messing around with them yet?

 

[MidOH]

Dpvs are a bit noisey.

 

[greeniguana]

Boat version will set you back a cool $5000.

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[The Ruttmeister]

I'm not a aerodynamics/hydrodynamics engineer... But as I understand it, toroidal propellors improve efficiency because they don't produce tip vortexes. Correctly designed ducted propellers shouldn't produce tip vortexes as the duct stops them from forming.

So while these propellers are significantly better than conventional ones, they shouldn't make a huge difference on a well designed DPV as they all have ducts...

I could be wrong though.

And it shouldn't be terribly difficult to 3D print some prototypes to find out.
Going to need to get a license if you want to sell them though!

 

[Jon Nellis]

There are propellers for speed and propellers for thrust. Toroidal props, like most open boat props. are made for speed. Ducted props are used for higher thrust at lower speeds, with the efficiency difference based on how well and for what speed the duct and prop are designed. As speed increases the drag of the duct becomes more detrimental than advantageous and at around 8-10 knots the duct will generally have more drag than the increased thrust it produces, making open props a better choice. Putting a toroidal prop in a duct would be a clear sign the person doing so, has no clue or that they are marketing to fad following people with no clue.

 

[Thrutch]

There are propellers for speed and propellers for thrust. Toroidal props, like most open boat props. are made for speed. Ducted props are used for higher thrust at lower speeds, with the efficiency difference based on how well and for what speed the duct and prop are designed. As speed increases the drag of the duct becomes more detrimental than advantageous and at around 8-10 knots the duct will generally have more drag than the increased thrust it produces, making open props a better choice. Putting a toroidal prop in a duct would be a clear sign the person doing so, has no clue or that they are marketing to fad following people with no clue.

Speaking as someone with no clue, thanks for the info!

 

[fishy.22]

Thrutch,
That is a great question. As mentioned above, the toroidal props used on outboards are beneficial due to the outboards not having the duct that DPV's have. In short, the toroidal part, is effectively creating a duct for outboards. Again, both of these methods increase effectiveness of the props by eliminating slippage from the under/over sides of the ends of the propellers, termed either slippage or tip vortices depending on the field of use.
The use of these ducts around propellers is most commonly called a Kort Nozzle, commonly used in the marine industry. As John pointed out, best used in low speed, high thrust designs.

Another form of improved thrust efficiency is the use of pre or post swirl recovery devices. Basically vanes that counter the direction of the rotating propellers thereby straightening the waterflow.