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safety dance/speed kills

Post of the Week

We like Anarchist RHough’s assessment of  wind limits, design and where it’s really at…

I cracked the books a bit and ran some numbers yesterday. I think I have a good reason for the wind speed limit being set where it is. Wow was I wrong. The boats ended up being faster than they predicted, i.e. the designs were too good. :-) This put them dangerously close to putting the foils into cavitation speeds (~50+) that could have lead to real control problems.

Basically they want to limit boat speed to under 50 knots to stay safely out of foil cavitation speeds. The boats can sail over 2x wind speed and in some ranges are close to or at 3x wind speed the TWS needed to keep them below 50 knots is in the 22-24 knot range.

The wind limit for safety was not a reaction to the Artemis disaster as I assumed incorrectly. I had assumed the limit was for structural concerns not an unforeseen design challenge.

If they want higher wind speed limits they have to lose the foiling to remove the “50 knot barrier” or they can lose the wing to reduce the top speed of the boats to under 3x wind speed.

If they want to keep the full foiling and hard wings they are stuck with a low wind speed limit until they solve the cavitation issue. Sort of ironic that the faster the boat is relative to wind speed the lower the safe wind speed becomes. If indeed the wind limit was lowered due to concerns about foil cavitation then they got it right and the engineering math supports it.

It is not about being pansies, or poor design, or reaction to the Artemis disaster. It is about unforeseen design success.

Stop bitching about the boats being to fragile to sail in 30+
Start celebrating that they are too fast to sail in over 25.

I’m surprised that none of the SA techies from AC33 had done the figures to reach this conclusion.

Cheers,
Randy

Jump in, people.

 

September 19th, 2013

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