Toroidal Props. Wow!

[Bowdrie]

Perhaps some variation/iteration of the design might be used on a tow-generator to gain some efficiency?

[fstbttms]

These props are designed for powerboats only.

[rslifkin]

Originally Posted by fstbttms

These props are designed for powerboats only.

How does a prop magically know what kind of boat it's on?

[AndyEss]

Thanks for sharing the article. Those props are beautiful, they look like Brancusi sculptures.

[fstbttms]

Originally Posted by rslifkin

How does a prop magically know what kind of boat it's on?

You think a prop made to fit on an outboard or outdrive splined shaft is going to work on your sailboat’s tapered shaft or saildrive?

[rslifkin]

Originally Posted by fstbttms

You think a prop made to fit on an outboard or outdrive splined shaft is going to work on your sailboat’s tapered shaft or saildrive?

Ah. That's a different problem. They're currently only making models compatible with outboards and outdrives. That doesn't mean the basic prop design isn't suited to a sailboat or inboard application, it just means they aren't currently selling them in that form (and may not have been tested enough to know if they're beneficial or not in those applications).

There's a big difference between "designed for powerboats only" and "only currently available in models that fit certain powerboats". The second statement is true, the first is not.

[wholybee]

Originally Posted by fstbttms

These props are designed for powerboats only.

They are currently in development, and currently being tested on outboards. That does not mean that they are developed exclusively for outboards, it just means that is what they selected for testing and demonstration.

If they make it to market, there is no reason to believe that they will not eventually be made to fit sailboats as well.

[fstbttms]

The point is, if you wanted one for your sailboat, you couldn’t buy one as a version of this prop for sailboats does not yet exist. Nor is there any evidence on the Sharrow website that indicates that there ever will be. My guess is that this type of prop works best in high speed, high rpm applications.

[AndyEss]

From the New Atlas article Chotu was so nice to post, there is an efficiency curve for traditional vs a toroidal propellor. I have unfortunately never figured out how to post photos on this forum.
That chart shows the toroidal prop to be clearly vastly more efficient from about 2200 to 4000 rpm. Great for fast running outboards.
I wonder if the toroidal designs can be optimized for about 1800-3000 rpm?
Those are the speeds my old inboard diesel engine spins at. I rarely go past 2500 rpm (assuming my tach is correct). Getting double the efficiency is something to consider -as soon as greater production decreases unit costs😄.
I try to sail as much as I can, so my dual diesel tanks last years on one fill up, so amortized fuel cost savings would have to be very substantial. I also need to consider that I am a bit underpowered, and have poor performance in strong currents, so 50-100% improved efficiency would solve that problem.

[StuM]

Originally Posted by AndyEss

I wonder if the toroidal designs can be optimized for about 1800-3000 rpm?
Those are the speeds my old inboard diesel engine spins at. I rarely go past 2500 rpm (assuming my tach is correct). Getting double the efficiency is something to consider -as soon as greater production decreases unit costs

I think you are mistaken, your figures would be engine RPM, not prop RPM. After going through a 2-3x reduction gerbox, most sailboat engines will go up to a maximum of around 1500 RPM and generally run at more like 800-1200 RPM.

[abarrow]

While it's clear that these props, as they are currently sold, are intended for outboards and planing hulls, someone commented earlier that this might be leaked submarine tech. I doubt seriously that sub propellers turn at 4000 RPM - more likely much lower. In their case, low noise might be more important than efficiency. In any situation where noise is lower, the energy used to create the noise is also no longer needed, so I would have to assume they would be more efficient.

[Bowdrie]

Originally Posted by abarrow

While it's clear that these props, as they are currently sold, are intended for outboards and planing hulls, someone commented earlier that this might be leaked submarine tech. I doubt seriously that sub propellers turn at 4000 RPM - more likely much lower. In their case, low noise might be more important than efficiency. In any situation where noise is lower, the energy used to create the noise is also no longer needed, so I would have to assume they would be more efficient.

Yeah, totally different from subs.
Subs have been using variations of this, (Ohio class sub).
Turboprop aircraft are also going this route, but with fewer and smaller blades that do turn fast.

[MicHughV]

It seems to me, that these props would incur a huge drag penalty when fitted to a sailboat. Might as well drag a bucket behind the boat.

[rslifkin]

Originally Posted by MicHughV

It seems to me, that these props would incur a huge drag penalty when fitted to a sailboat. Might as well drag a bucket behind the boat.

Any prop that isn't folding / feathering has that problem unless it has very little blade area for its diameter. It may limit the utility of these on a sailboat though.

[MicHughV]

Exactly my point, you can't feather or fold this prop.
In addition, with the shape of this prop, it's almost like having a solid disc there.

This prop seems to find it's niche in that 15" diameter range, whereas sailboat props are often of a much large diameter and operate at a much lower shaft speed.

Some might shudder at the price, but a max proo isn't exactly cheap either..

Innovative idea though.