America's Cup Disaster

Regarding tacking time and turn rate, allowance has to be made to get all the mechanics on the wing adjusted.

Not wanting to get into the cat vs tri thing but I suspect the cat with a wing-sail would have given the tri more of a challenge.

Duplication of controls? I have only crewed one performance cat but there was no such duplication.

In the end you sail in the conditions of the day. If you want media interest you declare the day and time well in advance and delay only if necessary to save lives, but if you have millions to throw around ...

 

I didn't think Ernesto was any sort of royalty. Is he really?

I don't understand the comment about taking the event far afield. Seems to me there was going to be a challenger series, same as the previous event that was so successful.

So what specifically was he doing that required one team to upset the apple cart and shut down all the other teams?

Seems to me sponsors were lined up and happy before the lawsuits started.

Without the Ellison lawsuit it would have already been at that place, it seems to me.

I don't think anyone is under the impression that LE is a model human being. At least I hope not.

 

Someone who knows

This would be a good time for someone with high speed multihull design experience to comment. Otherwise I think we descend permanently into discussion of history we can't change and the ethics of people we don't know.

Even uninformed technical speculation seems better than that. What is the name of this forum again? What did Bill say his intent was when he started this thread?

Maybe I should shut up. I'm sounding a like the PC police.

Peter Raymond

 

I agree it should be possible.

One way, (probably impractical), would be to run the races over a number of different courses, e.g. (just for sake of argument) announce 5 "candidate" sites along the east coast of the USA, and then choose 3 from those 5 by ballot.

Leo.

 

These boats have loads measured in tons. USA has one set of winches. Alinghi has one full set in each hull.

The power for the deck is centralized on USA, on Alinghi the power unit is in the middle of the rear beam, all the hydraulics must be duplicated for each hull.

It is not a matter of just having a set of switches in each hull, this is big, powerful, heavy stuff. Alinghi has almost twice the weight in deck gear due to the lack of central control.

USA's trimmers stayed at the centre hull, that is why you didn't see them having to run to centre to make adjustments.

R

 

Multi sanity

Hopefully, from now on, the AC will stick with huge multihulls.

They are everything the AC boats of the past were.

Big, grandiose, expen$ive, and the fastest type around.

The ACC monos they were using were flat out ridiculous.

Now it is essentially a 'Deed of Gift' race.

One with essentially no design rules.

It will take the return of 'progressive' taxes here in the States to bring back the design rule limited AC boats.

 

To add to the speculation on design hits and misses ...

Water Ballast ..?

One reason that Alinghi looked so hard to control is that they might have been trying to sail partially ballasted ...

That could be a huge free surface effect that tends to upset the boat. Could this be one of the reasons they started off demanding a wave limit of 1M. Simply the kinetics of the ballast system?

Smaller tanks or heavily baffled tanks increase the time to alter ballast. Did they take a chance and under baffle the tanks?

R

 

which raises the question of when the Alinghi team will spill the beans and give us the full scoop at to what was going on on there boat and why. They were desperate to halt the start of that second race

 

Now that's something I had not thought of, but I can see it is a real potential issue. Balancing movement predictability with reaction time could be a real nightmare. You want fast reactions, but you don't want your stability aid to become a liability in the same department. That may explain a lot of the ballast adjustment going on in fairly stable conditions.

--
Bill

 

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Waterballast has been used in ocean racers for decades-I'm quite sure that Alinghi's designers would have known how to design an effective system w/o free surface effects. I think that sailing without lifting foils(probably because of the negative effect on stability), having the boat too narrow and sailing w/o a wing were the causes of her control problems. See this thread: http://www.boatdesign.net/forums/multihulls/americas-cup-2010-race-thread-31452-4.html#post345707

 

Are you thinking transverse or longitudinal free surface moment? I don't know the boat's ballast tank arrangement, but if the tanks are completely within the narrow hulls the transverse free surface moment should be relatively small.

I read that Alinghi has 5 water ballast tanks. Smaller separate tanks should help to minimize the longitudinal free surface moment.

 

Longitudinal ... fore and aft movement amplified by a 75 foot lever would create a yaw moment that would alter the Angle of Attack (and thus drive/heel) from the rig.

surge forward = bow down yaw = increased AWA = more heel = need to dump power and steer up

steer up to course ...

surge aft causing overshoot on steering correction = lower AWA = less heel = hull in water = slow = need to power up and steer down ...

it could become an unstable cycle ... which is pretty much what we saw in Race 1 and to some extent on the reaches in Race 2.

Now I think it would be a pretty big miss to not have considered this.

It could be no more than the helmsman being behind the boat and over-correcting ... the result would be the same.

R

 

These would be the same designers that chose to hold their boat together with exposed struts and wires and didn't bother with a wing?

How about those "S" foils?

It could be that the sailors could not get the tanks full or tried to sail with tanks part full or just didn't get the memo "Ballast tanks must be 100% or 100% empty. Operating vehicle with partially full ballast tanks can lead to a loss of control."

What designers know how to do and getting it done are very often two separate issues.

R

 

Agreed. Minimizing the free surface effects is a naval architecture no brainer. The free surface moment due to movement of liquid in the tank is dependent on the dimensions of the tank and the density of the fluid. However, the amount of ballast and position of the ballast tanks will effect the mass gyradius of the vessel. That is much harder to assess than free surface moment and may have more influence on yawing and pitching motions than the free surface effects of water surging in the tanks.

 

Motion of the water and the effect of the increased mass moment of inertia as water is added might have made it harder for Alinghi to steer the boat, but that wasn't my impression as I watched. The rapid changes in direction were not continuous as you would expect if it were a yaw stability issue and if it happened going to windward, I missed it.

It looked to me like Alinghi was having problems controlling the height of the windward hull. It looked like as they lost pressure they were trying to keep the hull up by heading up. To convince myself I ran some numbers. If you were going 25 knts at 140 degrees with a 10 knt breeze, the apparent wind would be 18.5 at 21.8 degrees. This is close to an ice boat wind angle, but it's probably not hugely off. If you head up 10 degrees the apparent wind speed increases to 20.1 and the apparent angle goes to 24.4. Yes, better strength and better angle.

It didn't seem to be working very well for them though, because they would head up and the windward hull would still come down. If it were a dynamic yaw stability problem, I would expect unintended heading up to be matched with increased heel, not less. Also, they never seemed to have problems with the boat suddenly heading down.

Everything observed is consistent if you assume there were times when the pressure was dropping and they couldn't respond quickly enough. I doubt you can dynamically balance the boat by pumping water ballast. I just don't think it's fast enough. That leaves the sails. It's particularly tough to balance as the wind drops, because as the wind drops ahead of boat speed, the pressure drops and the angle moves forward.

If they could both depower quickly, but only USA-17 could power up quickly, or if USA-17 could power up further, that would explain what we saw. And this seems like the most reasonable explanation, especially at the speeds they were traveling.

Peter Raymond