# Mathematically-designed prop

Discussion in 'Surface Drives' started by sandhammaren05, Aug 4, 2018.

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### sandhammaren05Senior Member

I worked out a complete set of equations for pitch with rake, blade shape, and camber. The only adjustable parameters are pitch, diameter, and aspect ratio. The camber is set from an empirical condition that I discovered in 1978. The equations are adapted from (generalized from) wing theory. So far as I know no one has done this before but we'll find out when we apply for a patent. Our son (Maschinenbau student at TUWien) has used CAD to implement the eqns. and print out a 3D model. The model is shown without cup, our way of doing that is optimal and easy to spot with the eye so I won't show that. What makes this prop different cannot otherwise be seen visually. Next step is to make a CNC prop and test it on our SST45 tunnel.

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### Mr EfficiencySenior Member

Well, only the test will tell if it is "good different".

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### fallguySenior Member

Good luck Joe.

Is this all done for speed, or if improved, would it be better for all?

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### sandhammaren05Senior Member

My propeller modification since 1978 increases acceleration without losing top speed.
I have 4 national championship wins and 4 APBA OPC speed records from the 1970s-80s
to demonstrate that. The key factor is built into the mathematics. Furthermore, the way
that the camber is built in will lead to better thrust/drag than when I merely use a hammer
on an already-existing prop. It will produce better surface piercing props for racing and sport boats,
i.e., for about every application. I'm in Austria for another week. We need some hub measurements
from an SST45 prop in Houston before we can CNC a prop so we will race the prop next year, not this Sept.

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### fallguySenior Member

In most modifications, something is lost.

Have you lost anything?

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### sandhammaren05Senior Member

Something gets lost when I hammer on an existing design to improve it. Everything
is built mathematically into our design. Nothing is lost.

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### fallguySenior Member

Would the prop be less efficient at lower speeds Joe?

i.e. less low end torque?

That is all I am asking; politely.

And partly because I know you are racing these, see?

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### sandhammaren05Senior Member

It's very good at low speeds acceleration-wise. It gets us off the start dock from a dead stop ahead of the
other boats. I use exactly the same idea to rework existing props for our 1968 Glastron and
1965 Power Cat, and also for a much slower rib-inflatable boat that we run in Germany with a 1989 Johnson 50. As surface-piercing
props go it's the most efficient design that you can make, it's made for both acceleration and top speed (via the correctly set camber).

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### TANSLSenior Member

@sandhammaren05, the truth is that all this is a bit mysterious. I understand that you need to protect your invention but, since it is not possible to design almost anything without the help of mathematics, I would like you to explain, without revealing any secret, why and how mathematics have helped you to create such a good product.

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### sandhammaren05Senior Member

We don't know how good it is until we produce and test it. I adapted ---------- to prop blades instead of wasting my
my time with lifting line theory, bvp for exit and reentry, and other red herings. LLT anyway can't work for surface piercing, the bvps require hokey assumptions and results do not lead to better design. The complete math is in my book, which I will publish after we apply for a patent. I built into the math an important factor I've known since 1978, which gained me 4 national championships and 4 speed records in racing. Everything will look very nonstandard from the standpoint of a naval architect.

Last edited: Aug 9, 2018
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### TANSLSenior Member

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### gonzoSenior Member

At the end, the proof of the pudding is in the eating. It is hard to argue with race wins. I look forward to seeing your propeller design.

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