34th America's Cup: multihulls!

My calcs show a balance point of around 53 deg. I used a rig weight of 1325 kg and a rig cog 23.7 m (wildly guessed 1/3 the 68m span) above the platform. I ignored the crew weight.

I agree the wing lifted them back for sure with that reverse camber - what luck they didn't manage to release that. But on the other hand the initial turning moment (to port) from that reverse camber would have "thrown" them harder into the tack than normal.

 

Somebody (I can't remember who) asked a great question which has
remained unanswered:
Why don't grinders use their legs as well as their arms?

I suspect it might be easier to "disconnect" and move to the other side of
the boat if you only use your arms, but it should still be worthwhile to have
one or two grinders using their legs.

 

I mispoke. I found the post by tspeer that I was looking for and it did not say anything about a three second power storage. In fact, he said the system lost power immediately.
I don't know where I got the three second business from. Sorry.

 

Legs would give more power for shure, but the fatigue would arrive much sooner. The limit is imo given by the heart and the lungs, they allow the machine to produce the power.
The difference between leg-driven and arm-driven system would be just the gear ratio of the winch mechanism, again imo.
But I might be wrong, these athletes are possibly working somewhere at the borderline between aerobic and anaerobic. It would be so good to have a doctor in the house (forum) now, to give us a more scientific point of view.

 

One of the differences between a leg driven system and arm cranking is the ability to sense feedback. I doubt that would matter much as far as AC 72's are concerned, but that's a sad situation in my opinion. It appears that three sailors do 100% of the sensing and control, and are often overloaded, while eight guys supply power and have no real feedback that lets them actually sail the boat. I think this area may have been given short shrift in the boats original conception. That seems like a huge amount of resources to be throwing away.

 

The number I ended up with based on sports medicine at the time was a .5 HP burst and .33 HP sustained (long distance cycling) from this we get a mixed unit figure of 195kg/HP for sustained effort.

For my Rule 52 idea you take the sustained or burst power requirement to come up with crew number and weight. Then scale the boat to the power limits of humans. I have no idea exactly where that would end up but I suspect the AC72's are darn close.

@petereng, thank you for the explanation. I'm certain I had heard that there was some small amount of energy stored, however if TS says no I am happy to accept that the systems do not violate Rule 52.

The idea of allowing an accumulator to store energy for emergency use has come up. The consequences of using that stored power would be similar to using your engine to keep from losing your boat on a reef. I argued for DSQ if you had to break the seal on the emergency reserve.

 

Which is pretty close to my figure, +/- 10%. A reasonable difference in estimates, considering that we are talking about human metabolism, not about machines.

 

In my rowing model I assume that anaerobic pathways are important for the
first 45 seconds and aerobic pathways are dominant after that. I (and most
other researcherss) ignore creatine which is only important for the first
couple of seconds of intense activity, but it might play a role in grinding.

I think PhilSweet might be very close with his guess that feedabck is
crucial.

 

Correct. Long-term power production is mainly limited by O2 uptake and delivery rate (i.e. by the lungs and heart), not by muscle mass. This assumes that the grinding arms can consume all the available O2 rate of a very fit grinder, which isn't obvious.

Regardless, average power is degraded if the work is done in bursts, because you then have to go anaerobic intermittently which generates lactate, which produces muscle fatigue. Also, in a tacking duel the grinders will use up some of their available O2 just to sprint back and forth across the boat. That's wasted power that isn't going into the hydraulics.

I would seriously look at having several dedicated grinders sitting in the center of the boat, doing nothing but pedaling. A big pro cyclist (e.g. track time trial specialist) could certainly put out 350W-400W *steady state* for the entire race, and replace at least two or even three intermittent arm grinders. If the rules limit the energy storage, then a short-race specialist like a kilo rider could put out 800W or more in shorter bursts.

I assume the teams looked at the pedaling solution, so there must be some downside to it.

 

I think the higher wind favored Oracle. They seem to get better scaled performance out of it than ETNZ. Once the wind drops below 19 knots or so the Kiwis seem to enjoy better efficiency.
So to me the higher wind and the Ebb tide contributed to the better performance by Oracle. Hey, maybe that's the way they had thought it was going to play out and it hasn't until now. If the wind is at 15 to 18 knots and we have the tide coming back into the bay as in the first several races then the Kiwis may wrap this thing up sooner than later. I hope

Ive always been a fan of David over Goliath. I think we know who each team represents.
I am a California Native and I have absolutely no sentiment for Team Oracle and their crew of paid assassins from outside the country. Its an insult to all the very good sailors here in the USA.

 

Disconnecting from the machine and running to the other side might be slower.

 

Not if the pedalers are seated in the center of the boat all the time.

 

True. But there are disadvantages to that arrangement too.

As you said, it's almost certain that a variety of arrangements were considered
by the teams and hand-grinding won out.

 

Since Lord of the Rings was made in NZ it is now a contest between Team Orc and Team Hobbit.
Expect some strange boats in Auckland if NZ win

 

I have always placed value on simplicity. Having the controls and grinding stations duplicates on both hulls more than doubles the potential failure points.

The only crew that need to change sides on tacks/gybes are those the need visibility. There is no real reason to power the boat with grinders that are half winded from the tack to tack wind sprint. That means 6 or 8 crew could be stationed mid-ships inside the lower fairing to grind and power the systems. The advantages of simplicity and a more central centre of gravity should be measurable.

It will be fun to read the book about AC34 and the why we did that evolution of the designs.