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Sharrow props

$5k is almost nothing when people are dropping 50k on a motor. I am sure these might start coming standard on higher end motors eventually.
 
adrianp89 said:
$5k is almost nothing when people are dropping 50k on a motor. I am sure these might start coming standard on higher end motors eventually.
Click to expand...

I posted in another thread about Yamaha signing on as a producer and supplier of Sharrow props.


Typical gains thus far are a 40% increase in mpg / range, that’s huge. My friend and I are starting a multi year refit on a 1984 Wellcraft 228 Sportsman that was gifted to my friend from his uncle, part of that project will eventually be a repower with twin outboards and a set of the Sharrow props will be put on those outboards.
 
I would hope that with Yamaha making them, they'd at least check them out as determine if they'd help in our boats.....

Scream And Fly Magazine - Propeller Test: Sharrow vs. Standard Prop on Robalo R302

Robalo R302 Center Console / Twin Yamaha 300HP Outboards ▼ The conventional props tested on the Robalo R302 were stainless steel 15.25 x 19 (38.73 cm x 48.26 cm). The Sharrow props were 15.04 x 19 (38.02 cm x 48.26 cm). One of the most critical aspects of every center consoles performance is...
www.screamandfly.com
 
Julian said:
I would hope that with Yamaha making them, they'd at least check them out as determine if they'd help in our boats.....

Scream And Fly Magazine - Propeller Test: Sharrow vs. Standard Prop on Robalo R302

Robalo R302 Center Console / Twin Yamaha 300HP Outboards ▼ The conventional props tested on the Robalo R302 were stainless steel 15.25 x 19 (38.73 cm x 48.26 cm). The Sharrow props were 15.04 x 19 (38.02 cm x 48.26 cm). One of the most critical aspects of every center consoles performance is...
www.screamandfly.com
Click to expand...

I barked up that tree last month and, well, no. Fingers crossed that it's actually, not yet.

1661984302530.png
 
Good on you for writing them!

I didn’t think there’d be an application for our boats since the impellers are ducted and don’t, at least I don’t think they have the cavitation issues in the blade tips like a conventional prop does, but hey that would be something if they did make impellers that would get the same true advance that the props do.

We shall see!
 
I’m sure it won’t be cheap unless.. you would be doing some testing for them.
 
closed surface no tip to shed tip vortices...
 
If they made impellers with similar features / functionality I bet a lot of us would be all over it. Well a bunch of us anyway if the prices were similar as well.
 
I sent them an email inquiring about impellers this morning… we‘ll see what the response is.
 
As I mentioned in another thread, when I tested Skat Trak impellers the noise reduction was very noticeable at the helm, and when sitting in front of the CC, the reduction in cavitation was also very noticeable.
 
Pretty sure Sharrow magic isn't to useful in axial flow pumps... no to say there are not improvements to be had for the jet pumps...
 
84rzv500r said:
Pretty sure Sharrow magic isn't to useful in axial flow pumps... no to say there are not improvements to be had for the jet pumps...
Click to expand...
Agreed. The premise of the Sharrow is to reduce vortices produced by the tips. Shrouded axial flow pumps like ours don't have that issue because the water is forced axially, and has nowhere to flow radially. Sharrow is solving a problem that shrouded propellers don't have.
 
2kwik4u said:
Agreed. The premise of the Sharrow is to reduce vortices produced by the tips. Shrouded axial flow pumps like ours don't have that issue because the water is forced axially, and has nowhere to flow radially. Sharrow is solving a problem that shrouded propellers don't have.
Click to expand...

I agree with your assertion about “ducted” impellers and them having less tip vortices due to their ducted design, but our boats do have issues with cavitation for varying reasons, sometimes it’s bad sealing around the intakes that cause aeration, and other times like in my case where I reduced pitch for high altitude operation I get cavitation if I use too much throttle off the line. I have to wonder with what appears to be greater surface area in contact with the water if these props as impellers would not improve performance.

As I have said in another thread, Skat Trak impellers with their longer leading edge and greater impeller blade length are noticeably quieter via less cavitation. Sadly Skat Trak is closing their watercraft division.

The other area where the Sharrow props shine is less slip, or what Sharrow likes to call true advance. Sharrow props in some cases have a 70% improvement in advance when comparing same vs. same pitch rates.

I‘m not an engineer, but if the ducted impeller design could be improved by 10, 20, 30% that would be huge.
 
impellers-19.png
 
water has mass and the axial flow pump is accelerating that mass so at the expense of more parasitic drag more area getting the water moving will be better... also modifying the intake grate to top load the pump better is what the ski guys do..
 
Fun thing about the our pumps. They aren't what cause forward movement of the boat. They only generate a pressure differential. The nozzle does the work of generating the moving force. Jet nozzles (either liquid or gas) work under the premise of conservation of mass. If you put 10 units of water in the front, then you must have 10 units of water come out the back. NOW, if the density of the water doesn't change (which at our pressures and temperatures it is considered negligible change) then this assumption holds true.

Now consider that the nozzle has an inlet diameter and an exit diameter that are different. The inlet is larger. So you can move so 10units/minute of water through it. If those same 10 units of water must leave the exit that is a smaller diameter, then it must do so at a faster SPEED. it's the same 10units/min of water throughput, however it must speed up to escape through the smaller diameter. So, what we've done is add kinetic energy to the water.

Energy is equal to one half the quantity of mass times velocity squared. Momentum is described as mass times velocity (found in the kinetic energy equation). So you can see that adding that kinetic energy has essentially allowed us to "throw momentum" out of the back of the nozzle. This set of unequal forces is what drives the boat forward in a jet propulsion system. It's not the "grip" on the water, or the dynamics of how the propellor (impeller in our case) moves through the water.

As a thought experiment, say you're standing in a jon boat floating in a still body of water holding a cinder block. If you throw the block out of the back of the boat, which way does the boat move? opposite direction right?!? What happens if you throw a larger block? What about a smaller one? As you vary the mass you vary the amount of momentum you throw out of the back of the boat. Same premise with a jet boat, we're just throw a LOT of water out of the back instead of cinder blocks.

With that said, there is some additional interaction between the water stream from the nozzle and the surrounding water mass the boat is floating in; however this mostly goes away at high nozzle velocities. As noticed by the nozzle literally being out of the water when on plane. This interaction however, is how reverse and low speed movement works (which is also why it's so sluggish at low speed compared to high speed).

SO, the Sharrow prop really doesn't hold a ton of promise for us. We have an axial flow PUMP that generates a pressure differential for a nozzle. Additional grip or other thoughts are somewhat inconsequential. Those impellers above with long leading edges, and additional blade area are generated from dealing with cavitation and non-laminar flow issues that arise from either high horsepower application through undersized pumps, or poor flow characteristics into the pumps (like from light vessels in less than ideal water conditions and high speeds). The sharrow prop increases traction with the water, and eliminates the tip vortices that shed energy when you spin a fan in a fluid. Ducting an impeller (or propeller) has largely the same affect. Spinning that massive prop to 8k isn't exactly reasonable either. Most outboards and I/O setups have a gear reduction in the lower unit. Sometimes as deep as 2:1. So a Sharrow prop is likely spinning in a max range of ~3k or so. We spin our impellers well into the 8k range on modified boats. The physics of keeping that shape consistent at that rotation rate is likely a significant limiting factor.
 
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