34th America's Cup: multihulls!

I think I just heard from the on board microphones on Oracle, at 3:18 to start, "Who are we kidding"...

 

Looks like the wind picked up quite a bit!
Could be another shopping day.

 

34th AC

TNZ incurred a penalty seconds before the last race was postponed. The penalty isn't carried over to the next race. Racing postponed until tomorrow.
Damn wind limits.....

 

...

Iain Murray saying the day will be called off in a few minutes, probably.

The Artemis Curse.

Remember how Artemis always stabbed her suitors in the back?

Actually she was more vindictive than that, and she found more cruel things to do to them. This wind limit is her latest infernal notion.

...

At least I poured a great whopping tumbler of Black Label, a few minutes before this start. Too late to put it back in the bottle I suppose.

No more racing today; What a tease he is, Iain Murray.

 

Are you sure that the penalty was against NZ?
I reckon the Orcs dodged a bullet.

 

Serious shopping!

I read somewhere today that Louis Vuitton has a million dollar shopping bag, on display in their pavilion there.

Cheaper than sailing!

 

That could be an omen that we'll see giant spinnakers at the next AC in
Auckland.

 

Is this thread a good place to talk about what went wrong between the stated goal of no race cancellations and a 33 knot upper wind limit and the reality of the teams agreeing to a 22-23 knot limit?

The easy and obvious answer is that they simply erred on the side of safety after the Artemis disaster?

If this topic needs a thread of its own we should start one.

 

Nah, it's too late to worry about.
Start a thread about the next AC in Auckland instead

 

NO penalty incurred.

 

No new threads please.
That subject ought to be perfectly suited to this thread,
where we have these continual 23 hr intermissions between the races!

 

...

Photo tweeted by VSail/Pierre.

By the time ETNZ confound the safety regulations and win this, the Prada guy carrying the letter to challenge will have forgotten in which pocket he stored it.

Other interested challengers could then do a flyover with a banner they can drop upon the Prada Rib?

 

The answer is imo different. Back when the original speed limits were agreed nobody could foresee that design teams would soon find a way to make these boats sail at 45 kts in a 20 kts wind. It means that they ideally might be able to exceed 55-60 kts in a 33 kts wind, at which point the danger becomes a matter of physics - and not an opinion.

At very high speeds (which is generally above 50 kts, but in case of foils working close to the surface - like these - the limit is much lower) the foils enter in the zone of extensive cavitation, which breaks the lift force and can cause structural damage.

Should the rudder elevator start to extensively cavitate at high speeds (and, as said, above a certain speed they necessarily will), it's lift force will dramatically decrease and it will lose a big part of its pitch-control authority. It means that the boat would be left without it's only effective mean of countering the pitch-down moment from the sails. The pitch-pole would be non-avoidable, and at those speeds it would be dramatic.

The below graphs, for example, show how lift and drag coefficients of a flat plate vary at various cavitation numbers (the smaller the cav. number "sigma", the more severe the cavitation):



The strong drop in lift coefficient is clearly visible towards the left part of the graph, for any angle of attack. The situation is very similar for airfoil shapes too, such as the ones used for AC72 foils and elevators.

So, I believe that design teams and people in the AC Committee have actually realized that the speed potential of these boats has become so high that they would go into a self-destruction, unless a severe limitation on maximum wind speed is enforced. It is a fact based on physics of hydrofoils, the Artemis accident was imo just a trigger which served to put the new (and necessary) wind-speed limits into practice. The 23 kt limit imo comes from the talks with the teams, through which they have established that 50 kts is probably the max. safe racing speed for these boats.

Cheers

 

From "The Australian" :

'On Monday, Oracle Team USA officials proposed increasing the wind limit from 23 to 24 knots, saying the crews were capable of starting races in those conditions aboard their high-performance, 72-foot catamarans.

Team New Zealand declined.'

 

34th AC

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That's about this America's Cup and ok by me-but for future reference it might be a good idea to have a thread dedicated to that discussion....