Hi Jeroen. I’m thinking a duct is a good idea at least for learning. I imagine I’ll be keen to loose it when I’m confident enough. So I’ll start with the PM. Thanks for the advice. Matt
Another question here, the prop below seems to generate some attention on thingiverse but untill now there is no feedback of someone actually flying it in this topic. Please give your comments, maby we can improve the design.
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I came across this radical new prop design…
Reading and watching the video links, the boat version offers a 20% ish increase in efficiency.
“Speed at all RPM’s” improved etc.
Developed originally for quieter drones, it seems radical enough to be considered a breakthrough. It would seem to be a little safer prop design too (for our feet) as it has a “fold back” rather then “knife blade”.
I’d imagined there was a way to get rid of the cavitation (vacuum bubble from the trailing edge at high RPM’s) Greg Sharrow’s design is a reality. Tested and reviewed. “Ya can’t make this stuff up”.
Unfortunately the $2,000 usd price (for my boat) is not sustainable. My suggestion would be to use light weight materials (not SS). Without cavitation (vacuum and ensuing vibration) lighter materials could surely be used. What do you think?
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The only tests you’ll find are carried by Sharrow Marine themselves with other companies / universities making the reports doubtful to me.
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This design is protected by lots of different patents. Take care while replicating it, even for hobby grade use. Not sure how they would react if a community start to use it (or a variation of it), even for “non commercial” purpose…
Here are some of these patents :
Patents apply to commercial use. You can design it and print it and use it
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Looks interesting , I stared to play.
Then the last post from @Sliman_O came up . Guess I will read a bit before doing more
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That’s true, but what about designing it and posting it so that a whole community can use it ?
I was just playing to see how it would be done, I do not have the ability to do the hydrodynamics required.
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Here is video about the Sharrow prop.
I don’t think you have anything to be afraid of. What I ment is that Sharrow have put lots of ressources in R&D for this prop. I was also tempted about making a variation of it then read the patents which really covers from A to Z how to make it.
I am no patent expert, maybe can @pacificmeister chime in ? What do you think Merten ? Is it safe to replicate and post it so everybody can benefit from it ? My guess is that it’s still tricky
Anyone can copy the design of a patented product and share it if they want to. You just can commercialise it. No one can stop a DIY builder doing their thing. If they could, the 3D printing sites like grabcad would be in violation of loads of patents.
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Yes! All good, I am not worried about patents, All I was saying is I will read up about the design a bit more. I was just playing as the shape intrigued me as to how it could be achieved. As the propeller is effectively six blades not three I am not sure what the two pitches should be vs the offset between them vs surface area etc. Hydrodynamics is not a subject I can contribute with. All I did was I spend 15 minuets after seeing the post to see how to loft the ~shape. Any suggestions as to the required parameters ? Note I only used 3 sketches but if this was done for real >5 planes & sketches would be required.
In the video I posted you see a drawing of the blade angles
If a lift board costs 12000usd then a prop for 2000usd with 20% higher performance would be an easy spice to a diy build if you’ve got too much cash. It would be great to see it 
What is this?? A concrete mixer?
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Right and in addition, you can commercialize it and pay the piper when they come knocking for patent infringement. Good luck enforcing any patents on a bunch of DIYers. Even if commercialized, make enough changes and it should not be an issue.
Does it work?
So what do you think for dimensions? Keep the hub 65mm and make the blades have an outside diameter of 140mm?
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I am getting ready to pull the trigger on the Maytech motor myself. I would love the opportunity to print your prop as well. I just requested access via google. Thanks in advance!!!
Here’s a sharrow prop fusion 360 file:
Any input on what to do next is welcome.
In fact, there is a design error. A sharrow propeller is made of N loops (2 to 9 in the patent). Each loop creates a pair of blades that interestingly share the same leading edge. To understand this, you need to take a 1"x5" strip of paper (10cm x 2.5cm), make a cylinder making each extremity touch each other (no twist) and shift extremities on the same line.
In reality, on pict 3 below we can see that :
1- the two roots of each blade within a loop are not on a straight line
2 - the top of each loop is pinched
You must also read @Sliman_O patent information post 115 above. eg doc n°2 gives rake/roll/skew angles plus Alpha (angle of attack).
