34th America's Cup: multihulls!

34th AC

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Link appears to be no good-"Webpage cannot be found"

 

Try here

http://www.americascup.com/en/news/3/news/15572/regatta-director-presents-safety-recommendations

Richard Woods

 

Ac 34

Thanks Richard-that led right to it! The actual recommendations are in the PDF below.
First things that caught my eye were:
1) Rudder elevators(flaps?) allowed and may extend past maximum beam. They can be adjusted until the warning signal.
2) Daggerboard rake control to be carefully looked at to be sure each competitor has a viable and reliable system. Daggerboard rake adjustment changes the angle of incidence of the main foil and ,therefore lift.
3) 10 knot(!) lower maximum wind speed.
4) VII-"No reommendations can cover all possible risks or address risks specific to Competitor specific designs."
5) VIII- "Each competitor and crew member remain responsible for their own safety at all times. Each Competitor and crew member must continue to make their on decision to race or continue to race."
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Dropping max wind speed 10 knots seems like it will affect the boat designs a great deal.
The rudder elevator should improve pitch control and maybe even improve low speed takeoff.

 

I was a bit surprised by the high end wind limit that was set originally as it seemed a bit high overall but a max wind limit of 25 knots like the C Class would I thought have been reasonable. It's sad that it really does take a tragedy to trigger change if Artemis had simply pitchpoled and everyone survived nothing would be different.

 

34th AC

Wind limits were a source of ridicule in past America's Cups for being too low. Changing them at this point is something to think about. It seems like the teams will be going all out to get the boats to take off earlier(in lighter wind) than they do now. I could see significant main foil changes to go along with the big time rudder foil change. The whole foiling bit may be completely reconsidered.......

 

For those who want to continue to follow AC72 design developments, and those in other hot racing classes, I recommend going to http://chevaliertaglang.blogspot.com/ and signing up at the right to follow the blog by email.

 

34th AC

Thanks Stephen..

 

Those lower wind speeds may be a scheduling nightmare.Lots of early morning heats.pretty sad that all that money and all those very smart people couldn't build boats to sail in the conditions that there knew prevailed,

 

I don't expect they'll lower the wind range as much as these recommendations call for. A lot of their other safety recommendations are good new thinking 'outside of the box', and the absolute most relevant recommendation vis á vis learning from the Artemis accident, is probably item 1.1.

When they institute these ideas and are using the new equipment, the teams should feel a lot better about overall safety. As dramatic as it looks, having a catamaran airborne at 35 knots is in some ways less stressful than flying two hulls on a trimaran at the same speed.

It's a long time since I scanned through the rules for the 72, but it's my assumption that those rules would either have blocked or severely limited the Artemis team, had they wished to completely replace the beam following the notorious tow test in October 2012.

What looks like an inadequate repair job may have been a pretty good one nonetheless. That beam was put through quite a lot of stress before it eventually came apart. The only proper fix may have been to replace it altogether; but that was either strongly discouraged or impossible under the rule... ?

 

I have not followed this new class adoption well enough. I really need to do that as the whole issue interests me. My apologies if I am simply regurgitating what has already been discussed. Anyway here goes.

Let’s look at the rationale behind the class adoption. My understanding was that there was 4 prime objectives:

Increase the wow factor (more TV viewers)
Standardise design
Cut transport costs so that less wealthy teams could compete
Formula 1 status as regards speed

My understanding is that there was a lot of opposition from professional sailors when the change was announced. This also applies to mono hull designers who are interested in the supreme challenge of going that little bit faster.

I also have no doubt that there would have been opposition on the basis of safety. Hell even I could see this after viewing one race.

What has fundamentally changed?

Whereas mono hulls challenged the sailor’s skill and endurance the big cats under the original concept challenged skill, endurance and courage. The teams that could push to the limit of the safety envelope would be the most competitive. Ie ‘how big are your balls?’ This is not a good situation. What would you do if you were a skipper responsible for the welfare of your crew and their families?

Why are these boats potentially dangerous? Because of physics: Force= velocity squared. The forces rise exponentially in relation to wind speed. You are sailing along in a certain wind speed, pushing the envelope to max on one hull, and then a gust comes at double the velocity, forces quadruple, you are gone. The sheer size of these things makes capsize extremely dangerous.

So, finally the penny has dropped. Someone had to die before something is done in regards to what many would have predicted from the beginning. Limiting wind speed was the only option. The emphasis will now come back to intricate design and skill. The extreme wow factor is dead, thank goodness.

One thing we can be sure of: if the Americans don’t do well there will be class changes all over again.

M

 

34th AC

In the old days (monohulll AC boats) there was some grumbling because the wind speed for sailing was about at the new limits. It's pretty hard to explain to someone that here we have boats that represent the pinnacle of sailboat racing to many people, yet can't sail in wind over 23 knots.
The windpressure in Skenes shows that the new 23 knot windpressure produces a pressure per sq.ft. 37% less than the old wind speed. Thats a huge reduction!
I'm saddened to see these technological marvels subjected to this and sadder still that it took a great sailors death to cause such after-the -fact
re-thinking-probably before anyone knows what the cause was.
The good news is that now the designers will have to optimize the boat for lower speed take off. Thats good news because what they learn will help everybody involved with the design of small multihulls.
The bad news is the only other alternative is to eliminate foiling altogether.
I urge everyone who is interested in AC trikledown-which has already begun- to watch the 18' Flying Phantom video I just posted today-it is simply incredible:
http://www.boatdesign.net/forums/multihulls/flying-phantom-f-18-catamaran-43898.html Post # 8

 

Where does that come from, Doug?

 

34th AC

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Page 297, Francis Kinney's "Skenes Elements of Yacht Design", "Wind Pressures".
I used 30 knots as the previous limit because I didn't remember it exactly. At 30 knots the Lb. per sq.ft pressure is approximately 3.6.
At 23 knots the pressure is approx. 2.125 lb. sq.ft(discovered I miss read the first time) , so the new limit is 40.9% lower than the old limit.
Thats huge!

 

Ok, my mistake. I am obviously getting tired, it's late here. I had misread your words in the previous post, seeing the word "more" where it was written "less". Hence my expression of wonder... Sorry.
Cheers

 

34th AC

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No problem. Do you think this is a big deal-perhaps an overreaction?