Ultra-efficient toroidal propeller gets contra-rotating double upgrade

https://newatlas.com/marine/sharrow-contra-rotating-toroidal-propellers/

by Brajeshwar • 2 years ago

23 15 2 years ago

I can see $9000 as a fair price, but also expensive enough to buy one, scan it, and then CNC one of your own. I also wonder why it isn't coming out for two years, when they can already make them via CNC?

icegreentea2• 2 years ago

I think the prop includes the gear box needed to making it contra rotating. I also think the lifetime warranty being a pretty decent reason to not try to rig your own.

I imagine it's the gearbox that they're sinking engineering and testing time into. They don't have any other contra-rotating products on market, so the gearbox will be new to them.

SkyPuncher• 2 years ago

If I’m not mistaken, these shapes are rather difficult to CNC. Particularly, the inside of the outer part where a traditional CNC would be blocked. I think this might require robotic-arm CNC which is much slower and much more expensive.

I suspect they need two years to scale production

serf3• 2 years ago

I also wonder why it isn't coming out for two years, when they can already make them via CNC?

conditions testing and certification is a likely reason.

I can see $9000 as a fair price, but also expensive enough to buy one, scan it, and then CNC one of your own.

the gearbox and the process itself are expensive. the materials analysis and selection are expensive. the cfd is expensive. You're going to need a 5+1 axis machine at the least to perform the manufacturing.

fwiw I think the price is ridiculous, but normal, because unfortunately I have experience with the marine prop market and realize that anything 'marine' or 'yacht' labeled has a 250% markup by default.

a line from a sitcom occurs to me : 'This boat shit is expensive.'.

getwiththeprog2• 2 years ago

What is the potential savings on diesel though?

Can these be adapted to larger ships?

UncleEntity• 2 years ago

I can see $9000 as a fair price, but also expensive enough to buy one, scan it, and then CNC one of your own.

Ironically, that also includes the price of purchasing the CNC machine to machine it on.

To me this looks like it would be very beneficial to research the viability of lost-casting from a 3d print and do away with even needing to CNC machine anything aside from the precision bearing surfaces. Though, admittedly, I don't know how viable cast propellers are.

serf3• 2 years ago

Though, admittedly, I don't know how viable cast propellers are.

the vast-vast majority of marine propellers are cast first and then machine-finished.

the typical materials for marine propellers are usually very casting-friendly.

imtringued• 2 years ago

Ironically, that also includes the price of purchasing the CNC machine to machine it on.

You mean ordering a part on Xometry or what? A CNC machine capable of this type of work will cost more than a house boat. For your budget you would be able to afford a pocket NC at best. Have fun trying to machine a propeller with that.

westurner• 2 years ago

Beyond a general promise of better efficiency, agility and maneuverability, Sharrow doesn't dig too deep into how its toroidal blades might improve upon the benefits already inherent in contra-rotating propulsion.

Contra-rotating: https://en.wikipedia.org/wiki/Contra-rotating :

Contra-rotating, also referred to as coaxial contra-rotating, is a technique whereby parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. [...] Planetary gear

Epicyclic gearing (planetary gearing) https://en.wikipedia.org/wiki/Epicyclic_gearing :

By choosing to hold one component or another—the planetary carrier, the ring gear, or the sun gear—stationary, three different gear ratios can be realized. [3]

Other things boats and motors:

[Radial] Axial Flux motor: https://en.wikipedia.org/wiki/Axial_flux_motor

Koenigsigg Raxial Flux motor latest spec from YouTube, originally; 800 HP, 922-lb/ft or torque, under 40kg, but 750A800V=600,000W=60kW

https://www.thedrive.com/news/heres-how-koenigseggs-dark-mat...

Photos of the drive motor next to a roughly 11-ounce (330 mL) beverage can show just how tiny the Quark motor really is for its power output*

By comparison, a Panther Jeep Wrangler water car has a 4-speed manual "(3,664 cc) 24 valve SOHC V6 VTEC engine which produces 305 HP engine" with an engine weight of 160 kg out of a curb weight of 1,340 kg; and it looks like she drafts about ___ parked and ___ at 38 knots or pulling a waterskier.

Honda J engine: https://en.wikipedia.org/wiki/Honda_J_engine

Panther Jeep Wrangler watercar: https://en.wikipedia.org/wiki/Panther_(amphibious_vehicle)

But Axial Flux motors and geared toroidal propellers do not make MHD drives, which have no moving parts by comparison.

/? mhd drive: https://youtube.com/results?sp=mAEA&search_query=MHD+drive

MHD: Magnetohydrodynamic drive > Typology > Marine propulsion: https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive#Mari...

polishdude20• 2 years ago

Could you make a three stage cotra rotating prop? How about four? At some point it becomes almost like the compressor of a turbojet without the compression.

serf3• 2 years ago

it's usually about how much energy your setup takes to recapture turbulence into useful energy after the first spin, and it's a tight-rope act trying to figure that stuff out.

So yes, I imagine you could, but at some point those hydrodynamic gains run into the physics problem of spinning mass even if you can walk the turbulence tight-rope.

schiffern• 2 years ago

I wonder how contra-rotating schemes compare to something like PBCF?

https://www.youtube.com/watch?v=a8PjWSeLUzY

It seems like it should achieve almost the same de-vortex efficiency gains, but without all that added mechanical complexity, skin drag, and underwater noise (PBCF is actually quieter than having no fuel-saving device).

Honestly I'm surprised Sharrow doesn't already use it on their regular toroidal propellers. I notice a lot of hub vortex in their underwater videos...

dTal• 2 years ago

What would be the point? Contra-rotation has limited use as it is. In this case the stated reason is to ensure the axial flow has no energy wasted in twisting (though this can also be achieved with a stator) - in any case two stages are enough for this. The other main use is dissipating more power when you are up against some sort of limit on prop size, but this is not a common problem underwater.

getwiththeprog2• 2 years ago

I would like to see a desktop fan made from a toroidal propeller!

jakedata• 2 years ago

Given the number of times we ding a propellor on the plentiful rocks of the Maine coast, a generous warranty might make the $9000 price reasonable.

Ultra-efficient toroidal propeller gets contra-rotating double upgrade

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