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Savitsky calcs

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rynhardt
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Savitsky calcs

Postby rynhardt » Tue Dec 20, 2016 2:29 pm

I've been playing around a bit with Savitsky's planing hull formulas, and have gotten results that seem to match my own experience.

For example, the graph below plots the supported weight for a flat 1400mmx400mm plate at 4 deg AOA.

At around 15 knots (7.5m/s), my 90kg weight is nicely powered on my 1400x450 board. Of course, many other variables need to be taken into account, but as a rough guide the formulas seem to work nicely.

Anyway, attached is the original Savitsky thesis, and my little spreadhseet.
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SavitskyPlaningHulls1964.zip
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Savitsky board calc.zip
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weight vs velocity.png
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plummet
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Re: Savitsky calcs

Postby plummet » Tue Dec 20, 2016 7:26 pm

Is it considering board shape? Ie an ellipse shape like a mako gives away a lot of wetted surface areas compared to rectangular door shape.

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rynhardt
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Cloud C2 17
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Re: Savitsky calcs

Postby rynhardt » Tue Dec 20, 2016 8:49 pm

plummet wrote:Is it considering board shape? Ie an ellipse shape like a mako gives away a lot of wetted surface areas compared to rectangular door shape.
No. It assumes a flat rectangular plate.

But surface area and board width are the main determinants for the calculation.
I can do a sensitivity analysis on area and width, but I suspect area plays a bigger role.

What you can however do is take the results and scale it to your experience. Let's say you find a size and shape and rocker that works for your weight and conditions.
Now keep all the variables the same except for speed, and you should get a similar curve.

Or keep all the variables the same except for board length, and see at what minimum speed will it support your weight.

The idea is not to get "the answer", but to understand how speed, board length, width, rider weight etc affect each other.
Within a few reasonable assumptions I think Savitsky provides accurate results.


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