34th America's Cup: multihulls!

34th AC on Foils!

==================
Stephen I don't know much about wings-they should have done whatever Steve Clark says.
However, this boat was on foils when the incident began and with a foiler you want to keep the hull(s) out of the water! Resistance at that speed is not just frictional resistance its wavemaking resistance as well. I feel like if they could they would have wanted to increase lift on the lee hull using the manual control of the main foil(assuming that had not failed). Simultaneously, I would think the windward foil(at a positive angle of attack) should be dropped right then. Altitude is your friend. I think this would have worked if done immediately.
But they would have had to think about and plan for this.....

 

i Agree, "of course its operator error - it always is" - the boat cant capsize itself, nor can guns kill people all by themselves - someone has to pull the trigger...

The point is, looking at the video, those bows were submerged for a very long time - giving the crew adequate time to react - before the pitchpole reached the point of no return. So something could have failed that prevented them raising the bows and regaining control...

Does anyone have anymore videos of this boat actually sailing, before this crash or on a previous day? The only video i have seen shows it very unstable in flight - just like most other foiling cats that arent sorted out. They leap high into the air, bows pointed skywards then crash down for no reason, its all over the place...

And can someone explain how they can hope to control both foils, with different amounts of twist in the platform changing the AoA of the ww foil and lw compared to one another? How is this going to effect the pitch of the boat, when one hull is lifted clear of the water and dips back in, compounded with twist and 4 different angles between all 4 foils? Seems like a bloody designers nightmare to me...

 

=================
I have complete confidence in Oracles design-when they learn to fly it it will be very fast. As to controlling both foils-piece of cake- IF it is planned for. There is plenty of pivot to the Oracle foils. One thing that is not clear is whether the two foils are linked to the "joystick" at all times or do they disengage the windward one when they pull it up? 10 years ago a couple of guys flew Bradfield Raves in races using manual control of the two main foils and they had to control lift and platform roll(RM).
I imagine that if the linkage(whatever it may be) is disengaged to the windward foil, then they would have to have an emergency plan that one of the guys would deploy that foil in the blink of an eye if he gets the word or on his own authority thought a pitchpole was imminent. To hell with rules-keep the boat in the air at all costs!

 

Not particularly. Similar ideas apply in fast monos.... not even just in fast ones really, in really scary stuff in a Laser you are sometimes purposely over-sheeting the main to depower while trying to keep the bow up through waves. Tom Slingsby is a keen windsurfer (as well as someone who has lead the A Class worlds fleet IIRC) and as such would probably be very familar with oversheeting as a way to depower, as it's a standard technique in gybing boards. And techniques like oversheeting the kite through nosedives were run through over a decade ago in 49ers etc, as Nicho will tell you.

Just as some of these guys DO have experience at 30+ knots and yet still love sailing at 6 knots (contrary to the implication in your post in another thread) they also have experience with techniques like oversheeting and bearing away.

 

I've sailed a Catapult catamaran a lot, but with the older, smaller sail. It was light and fast, and would accelerate hard when bearing off, but the mast was short enough relative to the boat's length that I was never in much danger of sailing the bows under. I've sailed Hobies a couple times and once with the whole family aboard brought a 16 careening into a harbor with the leeward bow entirely immersed (the entire leeward hull almost immersed) with just the spray coming off the forestay bridal as it cut through the water. I've hit a moored boat with the Catapult because the Catapult accelerated faster than I could complete my turn downwind to duck behind the moored boat owing to my failure to pay the sheet out fast enough (stalling the rudder), but I've never pitchpoled or capsized a catamaran. So I agree that plenty of space should be allowed when bearing off, but I don't recall ever having the experience that releasing or paying out the mainsheet caused a problem (other than slowing down and dropping the windward hull) when sailing a catamaran. When sailing a Laser, yes (death roll), but when sailing a catamaran that's outside my experience.

I've done preliminary design work on two catamarans, the first being a 33 footer. Influenced by things I'd read about the Brendan Dobroth Canada's Cup winner Coug II (monohull) and the catamarans of Richard Roake I put the hulls' BMAX forward of the deepest section so the LCF would be forward of the LCB/LCG. The boat was never built, but we built and towed a model. The bows were very bouyant without being overly full.

I've had conversations with Richard Roake (when he lived in Newport, RI) who claimed he had a more informed approach than other catamaran designers concerning to how to keep the center of lift (by which I mean a hydrodynamic vertical vector on the bottom of the boat, as in planing boat design) forward when it needed to be forward. At the time Richard's Hardcore Hurricane and the custom 21' Worrell 1000 winner he designed for Randy Smyth had pioneered egg-shaped sections that were relatively fat & flattish on the bottom. Here's a recent design of Richard's: http://lindahlcompositedesign.weebly.com/lr4-build.html. He's an interesting guy, and in my opinion could contribute to a well run America's Cup campaign as long as there are others to keep him from straying too far from the evidence. He tends to put too much faith in his software and has not had as much success in A-class catamaran racing to date as, say, Pete Melvin. So far the cup teams seem to have stayed away from him, as far as I know.

 

Okay, gust is near or above 30 knots, boat is near crappy falls and current area; you've got an exceptionally high Bruce No. AC72 monster (around 3, maybe more, and that's to windward) whatever, extreme high sail area to weight ratio, huge flap mainsail ... you're going to sheet that in towards central with that load of wind in it, to stall rig out, quickly? - as the low bows disappear. Really!
Actually IF they could have sheeted in a little, a little, when the windward hull bashed down, maybe, maybe they could have lifted that hull out again - and maybe saved the disaster.
Carrying that extra area headsail in that wind strength was also asking for it, didn't help. Ask the high (but not extreme) Bruce No A and C Class sailors, they learn to tack with main only. And what is preferable - a few seconds slower tack ... and retaining a complete and un-wrecked boat?

 

Remember, the rules dictate the windward foil must remain raised. See post #649 this thread. Note that Tom Speer is a member of the Oracle design team.

 

That’s not correct. A gust is not a simplistic as that. There is a more defined and proper definition of a wind gust, which is:

"...the maxima that exceed the lowest wind speed measured during a ten-minute time interval by 10 knots...."

But it is also more complicated than that. Here is a table showing how to “convert” wind speeds into gust speeds:



So, for example, in the wind is “at sea” and say a 3 second duration over a 10minute period of sustained wind, you multiply the mean wind speed by a factor of 1.23, and so on.

 

34th AC on Foils

I think the foils should have kept the boat from pitchpoling as the foils were designed to be able to do. There may have been a failure in control of the lee foil and they may not have considered that they'd need to use the windward foil in a situation like that. The problem was a control issue-human and/or mechanical failure. The foils have the power to send that boat up at an almost 30+ degree angle so they should have been able to prevent that pitchpole. see pix below--
Why didn't they work?

from Scuttlebutt tonight
Witnesses say the team appeared to be wisely cautious, using only the small
headsail and keeping the hulls in the water rather than foiling.* The
defender had previously demonstrated their foiling ability, but had yet to
exhibit the same foiling control as the Kiwis. And with a strong ebb
pushing against winds estimated to be in the mid-20s, maintaining control
in the steep chop at this early stage of training was prudent.

But herein, quite possibly, lied the onboard conflict. Observers have noted
that the defender's AC 72 opted for a narrow bow shape design, which is
good for reducing weight and windage but does not prevent a pitch-pole like
a fuller shape. So how did the designers expect their AC 72 to avoid
pitch-poling in strong winds?

As team engineer Dirk Kramers explains, their AC 72 is supposed to be
foiling when they bear away. "Our hull is quite small, much smaller than
Team New Zealand's, so we are reliant on the foils to keep it from
pitchpoling in a bearaway," explained Kramers.
==========
*The boat was on foils when the incident began.

click on image:

 

34th AC on Foils

================
Thats true but yesterday deploying the windward foil in a planned way in response to that kind of emergency might have saved a lot of hassle. It would have been used to lift not pull down.

 

Doug,
Watching the video you posted at http://www.youtube.com/watch?feature...&v=drgglIebuQY I see the windward hull lift, but not the leeward hull, and I don't see anything about the boat foiling in the description you posted from SA. At what point do you think they were foiling?

 

Does any one know if a foil did break, was it the replacement or repaired one?

 

34th AC on Foils

---------------------
At about 7 seconds in: http://www.youtube.com/watch?feature=player_embedded&v=drgglIebuQY

 

Jeez, Ad Hoc, we're talking about an overpowered AC72 capsizing in "strong" winds and in a falls area ... and you come up with this pedantic, picky stuff, (but admittedly, academically correct) however in reality, veering BS.

 

Ah - the hull toward us is to WINDWARD! Clearly I was not watching carefully first time through. So it's the windward hull that never gets clear of the water. Perhaps that's what you've been saying all along...