Foiler Americas Cup

[Chris Ostlind]

I stumbled onto this bit this evening and liked it a lot.

http://www.sail-world.com/USA/Americ...d-Weight/58754

[schakel]

Originally Posted by bad dog

I get a "Forbidden" message to that photo link Schakel - is there another? Thanks!

The last photo was on the front page of BYM and they change that every day.

Here is the permanent gallery:
http://bymnews.com/photos/thumbnails.php?album=246

Very nice and enthusiastic pictures: Huge crowds, happy faces. Especially of Rolf Vrolijk (the head designer of this project of Judel & Vrolijk)

[schakel]

A very good interview on the design of the Americas Cup multis:

http://www.bymnews.com/americas-cup-33/nigel-irens.php

And what I make of it:

He leaves awful lot in between:

About the bows that both changed into wave piercing: An inshore bow instead of a classic of shore bow.
Well they both adapted to Valencia as sailing water. I still find it strange because on the other hand the Tornado is being called as most successful catamaran ever. And those bows are slightly upward. I do not know I would not be surprised if both team shows up at the real cup with conventional bows.

About cavitations: He admits that when a hydrofoil starts to cavitate it loses its lifting power and then the whole thing ends up in a big crash. Game over!
Believe me: that is a very likely outcome of the match. And when the Multi is bigger the chance that this will happen is greater from my intuition.
But I will have to do some calcs on that.

About the motor: Both teams really push the envelope in their designs so why not. On the other hand: I would be surprised if you hardly need them. Those who ever compared the amount of power on the sheets between a cat and a mono know a cat is almost nothing in sheet tensions. My guess is both team leaves them out.

About trimaran versus catamaran: He points out that speed is more important then manouverability. But when it comes to the last part: Then the tri will win.
My guess Alinghi wins with 5 minutes in advance in the first race. Then the second race is the same. Then BMWO throws the towel. Until it starts to blow real hard: The team that keeps the boat together and doesn't lose much speed will win. In that case the tri might have an advantage.
The legal part about the maximum amount of wind will be a mess.... I am looking forward to that part as well.

But there is nothing much to be said in advantage of this match except that the most part of the match will be about design and not about tactics.
We will see:
I know there were speculations about the date of the match and since both multi's are not in Valencia I guess the date will be far of.

Can’t wait to see that happen

[xarax]

Originally Posted by schakel

when a hydrofoil starts to cavitate it loses its lifting power and then the whole thing ends up in a big crash. Game over!
Believe me: that is a very likely outcome of the match.

Why is this so ? The whole structure can not withstand the fall so that cat continue sailing on both hulls until it is lifted up again?

[schakel]

Originally Posted by xarax

Why is this so ? The whole structure can not withstand the fall so that cat continue sailing on both hulls until it is lifted up again?

In a previous discussion with Rhough he pointed me out that the banana-foils are for about 40 % responsible for the uphold of the bow. The buoyancy is by far not enough to withstand the load and unless the crew doesn't react instantly by easing the sheet the chance of the whole thing flipping over is possible and fatal for the match. So this is the case where the cat is with one hull out the water.

As you point out this is changed as the cat is out of the water on both hull and drives entirely on the foils
This is the case in this movie of Hydroptère where you can see the cat going nearly horizontal when on both foils:
http://www.youtube.com/watch?v=xFJocBvj-_w
But when it lands on both hulls however the decrease of speed might be fatal.

These are the dimensions of both competitors:

SUI100 lenght 25m, mast length 32.5m (top to deck (strange) instead keel)
gives:
A5 length (LOA hulls) around 36.65m 120'
mast around 54.3m 178'.

Somewhere in these forums I read that an increase of 1 ,5 % is calculated as fatal But the chance increases when the size is bigger. And of course I can start of the changes in the Reynolds numbers in case of turbulent or laminar but I guess we all know that.
I am pretty sure we are not going to get to see the calculations both teams made.

I have a feeling the bigger guy doesn't win this race. But I heard they have until February 2010 to fine-tune the whole thing. Where replacement of hulls and masts are within the rules of the game.

[Doug Lord]

She sailed today first time:

[TeddyDiver]

I love gaff cutters Thou a "bit" modernized version.. But seriously, I wouldn't call these mains as a "bermudan" anymore..

[Doug Lord]

Another spectacular picture from SA:

[EdgewaterMD]

i understand wave piercer to have benefits of reducing pitching of boat and resultant variations in apparent wind over sails. in monohull speak, this is popularly known as 'mmmmmm,..., flap,flap,flap,flap,mmmmm,..., flap,flap,flap,flap,flap,'.

fast multihulls' lee bow may want to dive/trip as opposite-direction hull drag and sail's lift forces increase with speed.
but let's separate 'diving' from 'tripping' bow.

now, imagine designing/trimming the boat to handle the diving problem for the design speed in flat water. but then, here comes a wave,..., trip. with a large bow having lots of 'reserve' flotation in its flare (to correct a diving problem that should have been dealt with in design/trim as noted above), the boat may have a Large increase in the skin,wave,and shape drag as the oversized bow hits the wave! just the opposite of what we want whereas reverse bow has more modest increase in each drag component as it punches through the wave. no trip, no problem. but who knows, maybe destructive wave interference (think Inui bulbous bow) has some effect?

a-class catamarans have been abuzz with this for some years now. the nacra a2 site has some content and a-class racing results back up the talk.

[Doug Lord]

The gist of the judges ruling today is that-apparently-Alinghy's engine is legal. I think it is a positive development for high performance big boats-and as Hydroptere has shown can lead to extraordinarily high performance.

[EdgewaterMD]

couple questions - i've seen that trend has been for increasing percentages for the amount weight carried by foils of ORMA 60's for example. i saw mention of a number above, and would not expect either BMW or Alinghi to even consider getting lee hull out of the water, onto foil. is that correct?

i liked the link to sail world article above. if everything i said regarding piercer bow is true, wouldn't it apply to monohulls? someone go out on a limb here if that's what it takes and say when or why not fast monhulls will have the reverse bow!

is there an 'easy' link to the rules regarding design of the AC boats? besides overall dimensions, various mentions of rigid wing and water ballast, the engine thing has me pretty confused.

re revolution - i think best part is the well-deserved attention that it will bring to multihulls. of course the flipping over and breaking up thing may be hard to swallow, but what the heck - it's time for everyone to find out about multihulls and for every reputable YC to support a multihull fleet.

[Doug Lord]

EMD- SA is rough compared to most other forums but the AC section is frequented by very knowledgeable people-you can learn about applicable rules there:
http://forums.sailinganarchy.com/index.php?showforum=23
============
The last batch of ORMA 60's had the curved foils lift about 70% of the total weight. Speculation has the percentage a bit higher on DZ and CZ.
This type of foil system does not use an altitude control system and so could theoretically lift the whole boat. If it did that there would be a much greater chance of the foil ventilating and a crash. The likelyhood of a crash resulting from such an event is even more likely since if the hulls are out of the water there is nothing providing pitch stability. Both these boats may be using some nifty technology that may allow them to reduce lift underway ,if necessary-but that is pure speculation. I would watch for changes in the foil systems as time goes by...
In the AC leadbelly days boats broke in half, masts failed etc.-wouldn't expect less from these extraordinary boats.

[EdgewaterMD]

thanks for the link but i couldn't really find a straightforward guide to any rules driving the design - particularly the rules that have allowed for multihulls or given them dimension. i've seen mention of 90'x90' is the thing but also speculation that A5 is actually 35mx25m.

i think the normal advantage of a tri is the extreme righting moment of a well-behaved boat that can be built to be square in LxW, whereas the cat should become directionally unstable as it exceeds W/L of 2/3. I imagine the torque inputs to steering if windward hull is not held steady out of water would be tough to deal with in a high efficiency world (hi aspect rudders for ex).

but Alinghi is not square and has been accumulating experience with the 40'x26' x40's and A5 is demonstrating sailing in flat water.

there is less heeling required for the cat but neglecting differences in mast height, SA, and effect of lifting foils, i would think a tri that is maxed out with resp to righting moment would still be able to have advantage over a cat that is pushing the stability issue, especially in an imperfect weather/water world.

but toss in the new-ish lifting foils, engine, water ballast and it makes me wonder if an Alinghi tri can pop out somewhere else? are they locked in to A5 in any respect?

[schakel]

When they started this,BMWO racing had the help of Frank Gammas and the crew of Groupama. Ernesto from Alinghi just hired Loic Peron who has extensive experience on Big catamarans like Gitana 13.
http://www.gitana-team.com/en/gitana...gitana-13.aspx

Both Groupama an Gitana team also experimented with trimarans and foils.
They are actualy very far and when it become stable it might be a huge improvement for the sport. Just as in the early days of the kanting keels things will break and even capzise. I was once worried that when at 40 knots this would mean serious danger for the crew when hitting a stay during a nose dive. The experts neglected this and I hope I will not have to say : "I told you so" when somebody dies in this new high velocity-cup.

Strange but I getting more and more aware of the fact that yachtsman aren't safety freaks at all. In holland 95 % of the time that sea rescue or coast guard had to take action it was for sailing yachts in trouble.On the other hand it is one sport after soccer where most revenue is made. And this is for private investors instead of FC Ajax Or Chelski.

The pitch stabillity is being obtained with waterballast in the stern compartments of the windward hull. At least that is the only solution that I can think of. Boy would I like to go with the Alinghi Cat. They have around 8 month to practice before the new America's Cup begins.

Originally Posted by Doug Lord

EMD- SA is rough compared to most other forums but the AC section is frequented by very knowledgeable people-you can learn about applicable rules there:
http://forums.sailinganarchy.com/index.php?showforum=23
============
The last batch of ORMA 60's had the curved foils lift about 70% of the total weight. Speculation has the percentage a bit higher on DZ and CZ.
This type of foil system does not use an altitude control system and so could theoretically lift the whole boat. If it did that there would be a much greater chance of the foil ventilating and a crash. The likelyhood of a crash resulting from such an event is even more likely since if the hulls are out of the water there is nothing providing pitch stability. Both these boats may be using some nifty technology that may allow them to reduce lift underway ,if necessary-but that is pure speculation. I would watch for changes in the foil systems as time goes by...
In the AC leadbelly days boats broke in half, masts failed etc.-wouldn't expect less from these extraordinary boats.

[Doug Lord]

On the S foils at the Daily Sail today by way of SA:
--

One of the most revolutionary features has been the S-bend shaped daggerboards. We assumed that the top of the S was simply there for engineering reasons, to enable each board to be cranked down. But Jones says this is not the case. “They are radical. That was part of the testing program we did last year in Valencia, sailing on the Alinghi 41, we built some boards of the same concept. A normal tri will have a centreboard and some C-foils. You can’t do that with a catamaran, so this is the solution and it gives us a lot of options. The concept is that when you are sailing downwind, the board is half up or reduced area, but because it is an S it is rotated inboard a lot, so it has got a lot of horizontal lifting capability when the board is half down. But when you push it all the way down, because of that top part of S, it cants it back out and makes it more vertical.”