34th America's Cup: multihulls!

[Doug Lord]

Magnus of the Canadian C Class Champions from a post on SA:

I've never really said it publicly till now, cause everyone knows I am "the wing nut" and I get all hot and bothered about wings, but from about 4 seconds after the rule was cast everyone who was anyone knew the design race would be won in the water with foils, not in the air with wings. You only need to look at a few rudimentary VPP graphs to see the difference between foiling and floating to know that you want to fly as much boat as you can, because the drag goes up so fast in float mode and it goes up a lot slower in foiling mode. The big problem is control, because you cannot have actuated surfaces to control ride height you have to figure out how to manage the whole package to keep it on its feet, in a safe enough mode you can put your foot on the pedal.

We went back to traditional for a couple of reasons, the biggest being it didn't work, in our chosen configuration. I am not convinced the C-cat has enough power to make it work well enough at all, at least for Fredo and I cause of how we like to sail the boat downhill. The 72's can unfurl a nice big code zero and that offers a lot of power to get up on the foils efficiently, now the trick is to ride a bike with no handlebars so to speak. Foiling without automatic ride height control really is, "Look ma no hands!".

My guess is the focus on foiling will be downhill as upwind they may have to trade away too much righting moment to make it worth it. I haven't seen any real numbers recently so it's difficult for me to say either way. For righting moment remember that your foil as it kicks in essentially moves the center of floatation of the hull towards the middle of the foil. When 100% up on a foil the boat is rotating around a point between the middle of the upright foil and the horizontal foil, well below and inside the center of actual bouyancy. As such you lose some leverage and therefore lose righting moment so you can apply a bit less power, so the trade off needs to be worth it to go for it.

So yes, my vote is anybody who is serious will be foiling, as soon as they are going downhill.

PS, I wager the big white tubes are inflatable structures.

I cut it twice and it's still too short

[Cataphract]

Originally Posted by Silver Raven

Gopoday 'Cata'. Where did you hear & from whom ??? Something seems a tad odd to me. If you look & listen to all that's been said & filmed about the K1 'toy' in those pics & at that time - your 'heard' figures - don't stand up to reality - as I can see - -

It's blowing under 20 kts (no white-caps - which is under 14 kts) - the seas are flat as (no waves - that I can see) the 'toy' was getting up towards 40 kts if not faster. Yes/No ???

14 kts - wind speed times your 1.2 is = 16.8 kts
20 kts - wind speed times your 1.2 is = 24 kts

14 kts plus 20 kts divided by 2 = 17 times 2.4 = 40.8 kts of boat speed.

Guess it's not possible for a - to long - to short - to heavy - to big - to clumsy - to flat sided - to 'agricultural' hulls & wing etc etc bla bla - to do anything like - get a whole 72' wing-masted cat fully air-borne.

Guess we'll just have to wait for another 100 years or - have another look & believe what we see ??? ciao, james

Raven, not sure if you were being serious or demeaning, but my information was taken from the America's Cup website.
Here's another video from Team Emirates predicting that their 72 will hit speeds of about 20 knots upwind and 40 knots downwind:
http://www.youtube.com/watch?v=fcvAi...ure=plpp_video
(fast forward to 16:14)
Of course it's entirely possible that these numbers are inaccurate, but it seems pretty reasonable to me. We'll just have to wait another year until the finals!

[Silver Raven]

Originally Posted by Cataphract

Raven, not sure if you were being serious or demeaning, but my information was taken from the America's Cup website.
Here's another video from Team Emirates predicting that their 72 will hit speeds of about 20 knots upwind and 40 knots downwind:
http://www.youtube.com/watch?v=fcvAi...ure=plpp_video
(fast forward to 16:14)
Of course it's entirely possible that these numbers are inaccurate, but it seems pretty reasonable to me. We'll just have to wait another year until the finals!

Gooday 'Cata'. More like just interested - so I could find the source & learn more. "Demeaning" - never crossed my mind - curious for sure. I'd think that we are all trying to learn about the potential of these fantastic machines. I have a special reason to want to learn more due to my very long term involvement in designing, building & racing wing-mast catamarans & now to old to physically participate however still want to go sailing.

I have learned & experienced just how powerful these wing-mast really are & somewhere in the aerodynamics there is a hidden overdrive - that if they can find it - will give them the surprise of their lives & take them to a new - yet unexplored extra dimension of power sailing.

Due to the ultimate brute force & the pure boat speed that these rigs can produce which pulls the apparent wind - so far around to the front - so that - when they get really 'wound-up' they are sailing on a - 'loose-work' or a 'tight-reach' - for most of the time they are sailing around the course regardless of where the wind over the course is coming from.

I'm just so - - into these big fast machines - wish I could be there in person to see them race in San Fran. I spent some time there way back in the late 40's & 50's as we had some great friends that ran a water-front restaurant on the far-side just under the shadow of THE BRIDGE.

dEnjoy all that's happening - I'm green - for sure. ciao, james

[Doug Lord]

More Team NZ-the first Americas Cup foiler:

click--

[Doug Lord]

From the front page at SA:

icarus falling
Oracle’s L-foil failure on their AC72’s first day out was no minor snafu. With nearly a two-month build time for the hyper-engineered appendages, their engineers and designers must be freaking out right now trying to understand exactly how and why such an important structure broke. With the foil carrying more than half the weight of the boat in fully foiling conditions, it’s akin to a brand new Formula One car losing its front wheels on the first-ever test lap. Like Artemis’ expensive and time-consuming wing failure and repair, Oracle could be looking at the loss of a ton of development time exactly when they need it most: When the breeze is pumping through the Golden Gate.
================
On "foil assist" tri's like the MOD 70 the lee ama curved foil carries around 70% of the total weight of the boat. On full flying foilers , like the Rave, Osprey and Skat the main foils carry about 80% of the weight. Based on what I've seen I'd say the main foil of the AC72 carries about 80% of the weight with 20%(max) carried by the rudder foil, at least initially. These figures change as the boat speeds up with the rudder foil going from lifting to pulling down automatically with no crew action required.
Exciting development here-can't wait to understand the AC 72's altitude control system better.

[Zootalaws]

Originally Posted by Silver Raven

Still don';t see how they can 'police' the 'rule/s' without a very active 'marshall' on board.

They are fully telemetred, with movable/zoomable cameras and continuous uplink.

Easy enough to monitor what they are doing on board.

[tspeer]

Originally Posted by Silver Raven

Gooday all of you; How the heck does anyone 'police' the 'pull-down' effect while they are racing - as I see it - that is not possible unless there is a 'roving' unpire moving all over the deck at all times that each boat is out on the race course. Any idea's there ??? - ciao, james

You need to go to The ISAF RACING RULES of SAILING AMERICA’S CUP EDITION

47.3 Preventing windward daggerboard increasing righting moment
After starting, an AC72 yacht shall have the windward board draft stripe(s) visible so to confirm that the board is no more than 0.500 m below MWP, unless one of the following applies:

(a) the windward board does not penetrate the surface of the water for more than 15 continuous seconds;
(b) the yacht is within 300m of a mark;
(c) the yacht is within 30 seconds prior to and after tacking or gybing;
(d) the yacht is sailing less than 15 knots;
(e) the yacht is sailing at less than 90% of its performance relative to the other yacht(s);
(f) the yacht is taking a penalty.

So the prohibition about using the foil to increase righting moment is mainly in effect when sailing in a straight line, and is relaxed when doing major maneuvers. Basically, it's enforced by ensuring that the windward board is out of the water. I believe there is a protocol amendment in work that will further clarify the application of this rule.

[P Flados]

Doug & others,

Max static load is DRASTICALLY different than transient loads.

Lets take the design static load, say 80%. Then take a gust that tries to accelerate the leeward hull down at a momentay 0.5 G. Assume minimal slip on the foil & you have the foil loaded to 120% of boat weight.

These are gross oversimplifications, but only the strain gages can say what really happened.

[Corley]

I'm not sure if this has been posted on here before but it's the first time I've seen it. Loick discusses the BPV record but also about AC45's and AC72's and Energy Teams attempts at securing sponsorship.

http://www.vsail.info/2012/03/02/loi...to-vsail-info/

[oldsailor7]

I liked Lock Crowthers rule of thumb.
Work out the max static load and then multiply it by 600%. to allow for un-calculable shock loading.
That allowed a factor of safety without excessive increase in weight.

[Doug Lord]

Originally Posted by P Flados

Doug & others,

Max static load is DRASTICALLY different than transient loads.

Lets take the design static load, say 80%. Then take a gust that tries to accelerate the leeward hull down at a momentay 0.5 G. Assume minimal slip on the foil & you have the foil loaded to 120% of boat weight.

These are gross oversimplifications, but only the strain gages can say what really happened.

================
Well, we know that Oracle knows how to design and engineer a foiling AC boat-they were the first to foil an AC 45. But, TMNZ has forever won the cudos for having the first foiling AC boat in history-one of the most significant developments in the history of the Cup and in sailing. Their AC 72 is the largest full flying sailing foiler ever sailed and that is simply phenominal.
I have no doubt that Oracle will correct their mistake and fly their boat. But they will be the second AC 72 foiler for the rest of time.........
Such exciting developments!

[Silver Raven]

Originally Posted by oldsailor7

I liked Lock Crowthers rule of thumb.
Work out the max static load and then multiply it by 600%. to allow for un-calculable shock loading.
That allowed a factor of safety without excessive increase in weight.

Gooday - 'young-fella' - O-S-7 Esq - Lock sure did get that right. I can't remember how many times I've used his - 'X's 600%' rule - it has sure kept me out of a lot of bother. Thanks for sharing - sure hope others will pay sufficient attention. ciao, james

[Doug Lord]

Here are photos from todays Oracle Team USA AC 45 testing of foils. No clear cut 100% flight: (last photo was done several weeks ago and was widely suspected of being photoshopped. We now know that it wasn't)
More photos here: http://www.facebook.com/OracleRacingTeam
Photos for Oracle by Guilian Grenier-

[Gary Baigent]

This is COMPULSORY viewing:
http://tvnz.co.nz/sailing-news/team-...-video-5066890

[redreuben]

Wow !