Toroidal props

[sammdawson]

This just popped up in my news. The difference on the outboards is insane!!! Is anyone spinning one of these props on an inboard? We cruise at 3000 RPM, looks to be the ideal point of efficiency gain. I'm curious..

Toroidal propellers: A noise-killing game changer in air and water

 

[sammdawson]

 

[Captinlon]

Don't think it would fit on most down east boat. Something like that would be into my rudder.

 

[El Mar]

Smoke and mirrors. If Sharrow props were so great, you would see them come standard on high end boats or as an option.

So either they have a terrible business model or the props don’t work as advertised.

 

[sammdawson]

Nope not smoke and mirrors .. the article is from Jan 2023 about an R&D award to a team at MIT

It seems the minimum size for inboard is 25" diameter and the added length may be problematic w rudder shafts. I'm going to do some more digging, will share what I find

 

[Canyondiver]

Smoke and mirrors. If Sharrow props were so great, you would see them come standard on high end boats or as an option.

So either they have a terrible business model or the props don’t work as advertised.

My buddy’s dad has them on a Hatteras 65, and they work very well.

 

[Brooksie]

Very expensive. I'd move my rudder in a minute if true.

 

[BB_Offshore]

Sounds like Yamaha is onboard and casting them now for sales.

https://boattest.com/article/yamaha-cast-and-sell-sharrow-propellers

 

[ccc]

Biggest market = outboards. Very expensive, so only high $$ outboard guys can consider them at the moment (and then you have to buy 3-5 at a time…) As I understand it, they do very well at fuel efficiency and other things but lose a little at top end speed vs standard props. High $$ outboard guys giving up top end bragging rights = difficult marketing road ahead.

And yes, many / most modern inboard boats are drawn with minimal removal clearance behind the props, so any extra length required is a bummer. Especially if it means you might need a longer shaft also(?).

All of which is kinda funny when you consider the market is tripping all over itself finding space for 1,000-lb $50k hunks of spinning metal (and the genny to run it) to keep the boat from rocking; god forbid you spend money On something that only saves fuel at reasonable speeds.

And they look kinda funny. Sort of like 3-5 outboard motors on one boat used to.

 

[Roccus7]

The outboard video may be misleading since they're not reporting RPMs for the speed. I wish they did, because IF the sound drop was truly due to the props spinning at the same RPM, I would be interested. I'm thinking the noise drop is because of the efficiency of the prop, so the engines are running at a lower RPM to get the 40 MPH. I'd love to find something to "quiet" my boat starting at 1500 RPM, but it seems to be a function of the long, hard top canopy funneling in the engine noise to the helm.

However at $5K, and my habitual habit of putting the boat where 22' boats don't belong chasing stripers, it's probably not a good idea. I'll stick with aluminum props to save my drive train, and either spend the $100 to repair or the $200 to replace...

 

[RobBaker]

Take a look at the chart at 01.47
Videos — Sharrow Marine
at 3500 rpm the difference in speed is amazing. 20 vrs 32 mph They don't make a prop for my Yamaha 115 yet but I'd be all over this if they did.

 

[WoundUpMarine]

Take a look at the chart at 01.47
Videos — Sharrow Marine
at 3500 rpm the difference in speed is amazing. 20 vrs 32 mph They don't make a prop for my Yamaha 115 yet but I'd be all over this if they did.

60% more efficient at 3000rpm is wild. All I can think is the sharrow prop is getting the boat up on plane way earlier, allowing it to get all that speed. It must create a ton of stern lift.

 

[Roccus7]

Take a look at the chart at 01.47
Videos — Sharrow Marine
at 3500 rpm the difference in speed is amazing. 20 vrs 32 mph They don't make a prop for my Yamaha 115 yet but I'd be all over this if they did.

I rarely run over 2800 RPM for keeping my fillings intact, along with motor longevity and gas savings. So yeah, there may be gas savings involved. Additionally, those stats are on planning hulls and with my semi-displacement hull, the curve is completely different.

To me, if it really reduced noise across the mid-range RPM spectrum, I'd be inclined to look at it, but then there are those pesky ledges I deal with all the time. There are boatyards here that will NOT install SS props without reading you the riot act and warning you about all the money you will be spending in the future on drive system and lower unit repairs when that SS prop meets up with a ledge. As my boatyard said to me when moving here, "No matter how careful you are, it's not IF you hit a ledge, it's how many TIMES you will hit a ledge."

 

[RobBaker]

I wouldn't do it for the speed difference. My Sisu is fast enough I would do it for the reduction of noise at cruising speeds. If I could cruise at 20 mph with a significant reduction in noise I would be thrilled.

 

[Roccus7]

I wouldn't do it for the speed difference. My Sisu is fast enough I would do it for the reduction of noise at cruising speeds. If I could cruise at 20 mph with a significant reduction in noise I would be thrilled.

That's we we'd need to see the speed and noise vs RPM analysis on both planning and displacement hulls. Since we both have non-planning hulls, the noise reduction would probably less significant than the video of triple 300 HPs Yammies on a planning hull. That graph you cited is not what you'd see for you boat since our speed as a function of RPM is far more linear than a planning hull's.

 

[sammdawson]

Yep, I agree w much of the above. Most of my noise above 2700 RPM is engine vibration resonance in open spaces below deck. I've been looking into ways to quiet the propeller, and this seems legit, but like others have said, outboards seems to be where the biggest gains are.