Toroidal props, what do y'all know about them

[Tobra]

I was not hip to the magic of a toroidal prop until recently.

The shape of the blade is such, that, rather than bubbles tending to form in a concentrated area at tip of the blade, it spreads out this area, and greatly reduces bubble formation and cavitation. I watched a video of a prop in the water going 40 mph. The difference in cavitation was striking. Upshot of this is that a toroidal prop is greater than 100% more efficient that a regular prop. From a practical standpoint, you get double the thrust from the same power, which also would be expected to result in much greater fuel economy.

Downside is cost, as they are much more expensive to manufacture. Over time, I would expect to recover this expense through improved fuel economy.

Standard prop $500

Toroidal prop $5000

I don't know if this would scale up from a 1' diameter prop to a 30' diameter prop. If it would, seems like the Navy would be all over this. Oh yeah, they are super quiet too.

I have no doubt someone will be along presently who either wrote the book on this, or edited the book for the guy who wrote it.

[island911]

The biggest drawback to toroidal props is that you cannot (AFAIK) dynamically vary the pitch. Which is a big deal for air propulsion.

[cstreit]

Last Youtube video I saw priced them at 10x a standard prop. Cool design though... Definitely quiter and more efficient in certain ranges.

...but will they save you $4500 in fuel costs per the 500 vs 5000 dollar cost?

Great idea but the people making them don't understand economics.

[A930Rocket]

What shape props do submarines use nowadays? They are definitely not your standard looking prop.

[island911]

Originally Posted by A930Rocket

What shape props do submarines use nowadays? They are definitely not your standard looking prop.

[MBAtarga]

I'm not sure about the shape(s), but I do recall years ago someone (perhaps a European mfr?) got in trouble for selling machinery to some country (China? Russia?) that gave them the ability to make props to such tight specs that they ran more quite and hence more difficult for the subs to detect.

[wilnj]

Here is why military submarine propellers are kept secret

https://youtu.be/vA90DdR8KRY

[island911]

Here are some very interesting drone prop's that are designed (MIT IIRC) to be exceptionally quite...





https://fpvitalia.com/nuove-eliche-super-silenziose/

[911_Dude]

I believe these new props are nothing more than a fad. Throw them in the pile with Turbo Twister exhaust tips you see on trucks. Not a lot of cost effectiveness. Who cares if your boat toy's prop cavitates? It still goes plenty fast. Be on the lookout for these to be installed on boats with owners that have more money than brains, like the center console fishing boats with 4-5 450 HP outboards lined up on the transom. My .02

[Norm K]

Chinese knock-offs: coming soon to an Amazon distribution center near you!

_

[fireant911]

My professional background is in brass castings AND I served in the US Navy AND I have a 3D printer... but I know nothing about toroidal propellers except watching a video!

The toroidal design is amazing and has MUCH potential; however, other than this being a totally new design, I cannot see why the cost for manufacturing would be 10X the current cost. One of the current methods of producing a regular propeller (for recreational watercraft) is using the ‘lost-wax process’. This works very nicely and some very intricate designs can be made that cannot be produced using a traditional sand cast process. Still, there is a considerable amount of manual work that must be done while preparing the wax components as well as detailed finishing work to the casting itself. This new toroidal propeller would presumably be made using a lost wax or lost foam process AND certainly require some new procedures but NOT at ten times the cost, at least in my opinion. Tooling is expensive but that is offset once the volumes increase. Here is a brief video showing the procedures of how Yamaha makes their propellers using the lost wax casting method - https://www.youtube.com/watch?v=bnBFm9Xc5DE.

Naval ships are another beast! Their massive propellers are most likely sand cast using a technique of airset casting – airset uses chemically-bonded sand, almost like an amalgamation of sand and super-glue to make some really, really strong molds. A video of this process is here: https://www.youtube.com/watch?v=Di6fu7F2BxQ. The manufacturing of the controllable reversible pitch propellers are probably made with airset castings as well because the huge size and weight of the individual blades and then machined and assembled. Of course, no one knows how submarine blades are made… while in the shipyard the sub’s propellers were always cloaked under a HUGE cover. Attempting to make a toroidal propeller the size needed for naval ships and cargo carriers would be nothing short of EXTREMELY challenging… if possible, at all??? I bet some very creative minds are already exploring this avenue.

Off topic but interesting tidbit… in regards to Naval ships and boats, each ship and boat can be identified by their unique propeller noise by the enemy. To aid in hiding this ‘propeller signature’, hundreds of small holes exist on the leading edge of the propeller blade whereby air is ejected that aid in camouflaging this noise. I have no idea of how these holes are cast into the part as machining them in after the casting is produced seems impossible.

Toroidal blades for toy/hobby drones - this is an ideal application for 3D printers. Folks wasted no time creating and sharing designs of this (for example, https://grabcad.com/library/toroidal-propeller-2). This is great because 3D modelers can be some very inventive folks and will certainly be tweaking and experimenting with designs – this may very well be the same people that help lead a breakthrough for creating a design for toroidal-like blades for large seagoing vessels.

I think we will see a significant reduction in the price of manufacturing toroidal propeller blades because they can provide so many advantages.

[Seahawk]

I sent the link to my partner, who designs propellers (Michigan BS in aero/Stanford MS in aero) for a lot of what we do:

"I’m pretty close to calling BS on the toroidal propeller. I can see where they get the noise reduction, but there is no way it is as efficient. I believe the noise data, but the scale they are working and how they are doing the measurements makes me very suspect."

Much more but I didn't understand it...he'll get into the weeds faster than a Ferrari with bald tires.

Quick Sea Story:

In the 80's DESRON 32 was the surface group that chased Russian subs in the Bering Sea...I did one detachment for a month and we had a lot of contact time of their Yankee-Class submarine with the SH-60B helicopter.

The amount of data that is known based on the noise ant submarine puts in the water is incredible. We knew their side numbers

[cstreit]

Originally Posted by fireant911

The toroidal design is amazing and has MUCH potential; however, other than this being a totally new design, I cannot see why the cost for manufacturing would be 10X the current cost.

Yes exactly.

There's just no reason for it to cost so much.

[Norm K]

Originally Posted by Seahawk

Much more but I didn't understand it...he'll get into the weeds faster than a Ferrari with bald tires.

Okay, as soon as I get the opportunity, I'm going to steal this line.

_

[A930Rocket]

Originally Posted by fireant911

…Off topic but interesting tidbit… in regards to Naval ships and boats, each ship and boat can be identified by their unique propeller noise by the enemy. To aid in hiding this ‘propeller signature’, hundreds of small holes exist on the leading edge of the propeller blade whereby air is ejected that aid in camouflaging this noise. I have no idea of how these holes are cast into the part as machining them in after the casting is produced seems impossible.

In addition to how they get the holes in the blades, I’m wondering how they get air to the blades. I can only imagine there’s a compressor inside the ship, air is pumped through the shaft and distributed to the blade, somehow…

[fireant911]

Originally Posted by A930Rocket

In addition to how they get the holes in the blades, I’m wondering how they get air to the blades. I can only imagine there’s a compressor inside the ship, air is pumped through the shaft and distributed to the blade, somehow…

Bleed air was extracted from one of the stages of the gas turbine engines used for main propulsion (we had four LM2500 gas turbine engines - two in each main engine room). This pressurized air was cooled and then routed to the controllable reversible pitch propeller. This was 30 years ago though I imagine that similar methods are still employed by the Navy. Here is a quick read that talks about the systems but, unfortunately, does not explicitly address your questions - https://www.globalsecurity.org/military/systems/ship/systems/prairie.htm

[nota]

Originally Posted by MBAtarga

I'm not sure about the shape(s), but I do recall years ago someone (perhaps a European mfr?) got in trouble for selling machinery to some country (China? Russia?) that gave them the ability to make props to such tight specs that they ran more quite and hence more difficult for the subs to detect.

https://en.wikipedia.org/wiki/Toshiba%E2%80%93Kongsberg_scandal

race boats both drag and offshore depend on their props
I have NOT seen this new ghimmic win races