# 34th America's Cup: multihulls!

Discussion in 'Multihulls' started by Doug Lord, Sep 13, 2010.

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### sharpii2Senior Member

So the 34th America’s Cup is finally over.

I see “Team Oracle” managed to win with eight straight victories.

Seams a bit spooky to me. How can one possibly win eight straight victories in a race that is supposedly even matched as this one? Even when the other team was regularly winning, they would lose about every 3rd race. Hmmm.

Anyhow, what is done is done.

Congratulations to Team Oracle!

Just for the fun of it, I scaled an AC72 down to the size of a “Hobie 16 ®”, and an “Hobie 16 up to the size of an AC72.

This should give a clue as to how extreme these AC72 boats really are.

If a Hobie 16 ® were scaled up to the size of an AC72, for instance, it would need 192 crew!

An AC72 scaled down to the size of a “Hobie 16 ®” would be:

Length = 5.05 M
Displ. = 77.3 kg (including crew) (D/L = 18.5)
SA = 11.3 SM (S/D = 63.5)
Crew Wt. = 11.2 kg
Mast Ht. = 8.79 M

A “Hobie 16 ®” scaled up to the size of an AC72 would be:

Length = 22 M
Displ. = 28,800 kg (D/L = 76.7)
SA = 414 SM (S/D = 44.1)
Crew Wt. = 17,300kg (Hobie 16 w/2 crew)
Mast Ht. = 35.2 M

As you can see, the crew wt. of an AC72, scaled down to the size of a Hobie 16 (r), would that of an average size toddler.

Strange thing is, despite the unbelievable top speeds, these boats averaged only 15 kts around the course. Seems a bit paltry …for all this expense.

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It's not two sticks-read it again! Interceptors are well known and have some pretty unique advantages. I'm hoping Slavi and Peter will interject some wisdom.

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### salglesserJunior Member

Hi Doug,

We make knives (Spyderco.com). All of the crew, chase boats, etc.,

sal

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### markdrelaSenior Member

These "interceptors" are known as Gurney Flaps in the car racing business, where they appear frequently on racecar wings to increase downforce of a wing with given area.

They are also known as Gurney Flaps in the aero business. But they are almost never used on aircraft, because they also significantly increase profile drag, and greatly increase the nose-down pitching moment, both of which are bad.

One refinement is the Divergent Trailing Edge developed by Preston Henne at Douglas Aircraft. This is sort of like a smoothed-out Gurney Flap, but which has been properly designed rather than slapped on as an afterthought. DTEs were developed specifically for transonic airfoils, for which they are most effective. By moving the loading from the top to the bottom surface, the DTE reduces the peak velocities on the top surface and thus reduces shock-wave strength and wave drag. This can offset any viscous profile drag added by the DTE.

Reducing upper-surface velocities will also certainly benefit a cavitation-limited hydrofoil. So it's quite possible that these "interceptors" improved the Oracle boat if they were used there. If so, then a DTE would work even better. Or not -- it's a benefit/loss tradeoff problem.

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### markdrelaSenior Member

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First Foiling AC

Mark, thank you very, very much!

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First Foiling AC

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Thats pretty cool, Sal! Thanks..

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### SkyakSenior Member

Hi Laukejas,

I have a couple comments on your post. The impressive graphics were created by Stan Honey's company and are even more impressive when you consider there are no fixed positions for reference. The technology is specifically aimed at making sailing approachable for viewers with no experience and I consider it a very expensive gift to sailing. Stan is a very accomplished sailor and navigator on numerous record attempts.

About the professional coverage that never said the word 'cheat', my understanding is that Oracle (Larry) had to pay not only for the coverage but also to air the race on cable TV. If Larry said all interviews would be naked spelling bees and aired in place of the nightly news it would be so. I have no idea how 5 pounds of weight in the kingpin would do anything to help unless there was some vibration problem. AC45 was just good practice. I can not believe anyone beyond the expelled participated in the cheating and I am sure the greatest violation was to OTUSAs top management. I imagine the cheaters are in disbelief of how stupid their own actions were. Pro sailing is a small world and they hold incredible grudges.

About the cup, it has always been THE big bucks, no holds bared, peak of sailing technology excess. I would call this cup a great success if only in the ratio of sailing hours to lawyer hours. If you like J boats or 12 meters there are classes still out there racing -ironically not often because of rule squabbles. The AC 72 is actually reasonably seaworthy compared to most modern AC boats and considering their speed. The previous AC had much lower wind limits (an attempt by alighi to give advantage to bigger 2D sails) and the last monohull AC featured boats that broke in half and sank frequently in moderate weather. Even the original J boats were designed so light they were considered not safe to sail beyond the race series. The AC72s do over 50mph in 20mph wind, it was not a bad decision to limit the races after Bart's death. We are lucky the lawyers didn't kill the whole program.

As I said, the AC is the ultimate high end development sailing class and I would say this year they delivered more performance increase than ever. And the big surprise was it was actually exciting! There has never been a comeback like this ever and increases in speed have historically resulted in big lopsided better-boat-wins-by-a-mile boring races. The the last three ACs have each cost more than a billion dollars. In my opinion this is the first that was well worth the cost.

9. ### El_GueroPrevious Member

OK, I need better illustrations, or better descriptions.

I found what little I could on google, mostly about their being banned in some class and what they were doing as work arounds .....

wayne

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### DCockeySenior Member

IF "interceptors" were added they should be obvious in a photo of the boat with a foil out of the water.

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### RHoughRetro Dude

Winner!

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The most recent foil picture on the Oracle site by Guilain Grenier taken in January. That's interesting. There must be more pictures.

click-

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14. ### El_GueroPrevious Member

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