34th America's Cup: multihulls!

34th AC

Final day of practice-JNavas video. http://www.youtube.com/watch?v=ua41YUZgwNk

 

Great Artemis shot BB. Yes I've been following the AC since Aus won with the winged keel. Its a shame Artemis couldn't get serious earlier. The blue boat certainly looked to tick all the boxes. But I think next time around the wing will go and the foils will stay.

One thing on my list has been to do a size study on foiling boats and determine if there is an optimum size for say the AC. eg now we are not restrained to the longer the boat the faster it goes what is the limiting factor? Size in terms of structural limits? ie as the structure grows it gains weight to the 3rd power or more. But the drive gain is by the sail area so there must be a cross over when its too big. or can the C-Class go just as fast? C's have limited beam width for their sail area so probably not unless they use the windward foil to hold them down (increasing Rm) Could AC35 just be in foiling AC45's, absolutely yes but is this what we want? Hmmmm more grey matter time needed....

Cheers Peter S

 

Good analysis.

 

To follow this thought up - The AC45 weighs (with crew) 1825kg, the AC72 is 6835kg. The AC45 has a SA=130m2 the AC72 has SA=340m2 (without spinakers). This means the AC45 has a power to weight ratio of 71m2/tonne, the AC72 has a P/W of 50m2/tonne. So the AC45 is supercharged compared to the 72!!. An 18 footer skiff has about 70ms/tonne as well. But the wing has twice the lift so can't compared directly. But seems to me that a smaller boat then 72 foot can go just as fast??

To add to this the C-Class has a SA=28m2 and no weight limit but they weigh about 334kg, so the P/W is 84m2/tonne so they can go faster if they can create the Rm. So they have to use the windward foil to hold them down and they could go faster then all of them!! this is if the P/W ratio is the limiting factor.

Peter

 

34th AC

Seems like I read somewhere that the foil chord is like waterline length in describing a maximum foil speed like waterline length does to some extent for a hull? maybe related to foil loading?
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To all the TNZ supporters: Best of luck! I'm only a halfhearted supporter of the Oracle guys(if that) because of the results of the Jury probe this week. There is just no excuse for a management system that allows that sort of thing. And Dirk De Ridder was knee deep in it-I'm appalled. To me it is profoundly sad for the America's Cup and trashes so much of the excitement this match was offering up. I couldn't be more upset.......
But I will enjoy the hell out of the racing and just hope it is good enough to make up for the recent cheating-if that is even possible. Dalton has said they would go back to monohulls and I think that would be a major tragedy so I guess the only choice is hoping that doesn't happen.

 

I think the Dalton monohull comment is a very old one and it would be interesting to hear his current opinion. His smile is quite big these days and I bet his smile would be much smaller on a mono. L. Francis Herreshoff, a legendary American designer once said: "The fun of sailing is proportional to the speed of sailing." and I think we have finally broke through the mono vs multi standoff. Racing is about speed and displacement monos don't have it. Perhaps the days of sausage racing is over and we need to develop race tracks to get the interest up... perhaps a figure of 8 to add some drama?/ Cheers Peter S

 

Finally come to your senses and swapped to the dark side eh Doug? Welcome to the winning side Cmon ETNZ

 

Re: foil loading ... yes Doug foil size ie loading is the limiting factor for lift. If the foil is too small it will cavitate and the boat will sink. This is whats limiting Moths at the moment. If the wing(the foil on the daggerboard) is made much bigger its drag limits the speed, if they make the wing smaller it does not have the lift. To solve this they need to go to ladder foils or V foils, a step they have not taken yet. I have talked to a fellow about a ladder foil but its a bit radical for them yet. To add to the P/W stats a Moth has a SA/weight = 70m2/tonne. So perhaps the optimal size problem starts by identifing the cavitation limit and then working up to the boat size. Cheers Peter s

 

Well said Doug. "its not if you win or lose but how you play the game" is the old saw...and how the game was played is what will be remembered from this one. Plenty of time to work on whoever wins to keep the foiling....A boat that could reef and races in a breeze would be pretty spectacular.

 

Loads are what you need to look at. Use RRS Rule 52 (Manual Power) and the power to weight ratios of V1.1 humans. At some size/wind speed the number of V1.1 humans required to power sailing systems becomes a practical limit. Innovation from Zero Stored energy and the use of hydro and aero forces to servo the trim loads to V1.1 human levels and there is no requirement for any dimensions.

I think such a rule would be elegant and the trickle down would be systems that make all boats easier and safer to sail.

Trim loads probably means keeping wings for race boats, but low power required systems would apply in many places and on a wide range of vessel sizes.

;-)

R

 

34th AC

The Jury dismissed the ETNZ protest against an Oracle gizmo-at least they won one.......maybe another one tomorrow?!

 

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It's race day!
A gorgeous morning here, out on the terrace reading the latest.

Hey, the ETNZ guys are said to be focused on weighing in, meeting the combined team weight of 1012 kilos (92 kg average per crewmember).

I've weighed exactly that for as long as I can remember! Call me, ETNZ, if someone on the crew has suddenly gotten too fat!

lol

Here's the delightful latest ETNZ video:

 

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And here is Team Oracle's pre-race video, Spithill and Macbeth make excellent comments, along with some aggressive music and splendid video of their two boats speeding:




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Back when Ellison won the cup in 2010 and it was slated to move to San Francisco, I suggested (on TheDailySail) that Jimmy Spithill had a lot in common with the looks of Steve McQueen's character in the movie Bullitt; that the car-chase music from Bullitt would make a good soundtrack for the AC34 movie.

... That was of course in the days when Vincenzo Onorato and Gavin Brady would be appropriately in the other vehicle, as the bad guys!

Now it seems that plot might need a little rewriting?

lol

Back to the music, that track in the video above is a good contemporary fit with Lalo Schifrin's 'Shifting Gears', which so effectively accompanied the hair-raising driving up and down the hills of San Francisco.

Maybe I'll play it during the countdown.

 

Just put "Cheatin'" into the youtube search bar.
You'll find a huge amount to serve as a soundtrack for the series.

 

I'll remember to do that, Leo, if I see that Tom Ehman and David Boies happen to be on the committee boat today.