34th America's Cup: multihulls!

[high on carbon]

As far as I can tell, the wing sails of the AC72's are made of two or more vertical components, which are themselves vertically continuous, kind of like an airplane wing with one or more very large flaps, one behind the other.

I am not aware of these of these components being divided vertically, like the sails on a square rigger, with a mainsail, a top sail, and a top gallant sail. If this were the case, the remedy you mention for being over powered might work

From the pictures I have seen, I can see no such vertical divisions. Correct me if I am wrong.

Or are you saying that each of these two or more vertical components can locally morph its airfoil camber?

Sharpii.

To follow up on an earlier speculation / post you made which I copied above.

Yes that is precisely what wings can do, locally change their camber to the desired shape. Be it on a C-cat or an AC 72, we can 25 degrees of camber at the foot of the wing, perhaps 5 degrees of camber 75% of the way up, and -5 degrees camber at the tip if we wish. additionally on almost all C-cats, and the ETNZ designed wings we can also twist the Main element more than 15 degrees between the foot and the hounds to accommodate twist in AWA due to gradient effects. This allows us to have the desired camber across the entire wing section, and combine that with the desired angle of attack, for any given section of the wing, to match the desired lift characteristics we are after. In short, it's a far more sophisticated approach than can be achieved with soft sails.

In this regard wings can be "bottom loaded" as discussed here, where you put all you drive down low, and therefore reduce your heeling moment, or you match your heeling moment to your righting moment, and take as much thrust down low as you can match to your available side force from your foils, while you flatten off the top of the wing or in some cases invert it, to optimize down wash distribution, the aim being to minimize induced drag from the sail plan.

your observation that the wings are made up of two main elements is correct, but unlike airplane wings, they are not as torsionally stiff as you are imagining. They are designed to be somewhat flexible so they "blow open" then the trimmers can control the amount of twist by limiting it with the control systems. On AC 72's these systems are string and hydraulics. On smaller boats it's pretty much all strings. you cannot see much of the trim systems on contemporary wings as they are mostly buried inside the wing to keep the wing slippery, e.g. low drag.

Additionally some of the flap elements are in fact in separate sections with slip joints between them. as the flap structure twists the leech must grow in length to accommodate the twisting, frequently this is happening at the joints. You cannot see it, because it is subtle, and we tape over the joint to prevent air flowing through the gap. on wings without a straight hinge line, this is especially important to allow the wing to twist correctly and maintain fair curves.

I hope this aids your understanding of how a wing works in mechanical terms.

 

[Mikko Brummer]

You are correct. The wing could safely sail in winds higher than the reefed soft rig. The wing sail has no need to reef. The power of the sail can be reduced to zero. The CE can be very low to provide the required amount of heeling force and the area above used to provide extra RM. This is a level of safety and control a flogging soft sail cannot match. The only reason to reef a soft sail is because it cannot be de-powered without flogging itself to death. If you want to learn something about light multihulls with tall rigs, you should look closely at the wing trim. In breeze over 15 the top of the wing has reversed camber. It is NOT adding to heel nor is it trying to pitch pole the boat. The top 1/3 to 1/2 of the wing is adding to RM.

Think again... if the wing is producing lift to windward in its upper half, it is also producing negative drive there. Helpful for the righting moment, yes, but not a very fast mode of sailing. Or am I missing something here?

 

[Mikko Brummer]

Not true either that soft sails cannot be inverted in the head and produce support against heeling moment. Well designed and trimmed, they do it automatically, whenever needed in a gust or when passing a wave... something a stiff wing will not do. The Europe sail model on the left (bad pic, video quality in mid 90's) was perfectly stable in the wind tunnel, at an apparent wind angle of 13 degrees, with the head completely reversed and producing negative lift. Not much drive there, though. The Star pics show the effect when sailing for real.

 

[RHough]

Think again... if the wing is producing lift to windward in its upper half, it is also producing negative drive there. Helpful for the righting moment, yes, but not a very fast mode of sailing. Or am I missing something here?

See high on carbon's post.

 

[markdrela]

Think again... if the wing is producing lift to windward in its upper half, it is also producing negative drive there. Helpful for the righting moment, yes, but not a very fast mode of sailing. Or am I missing something here?

Let's say the top section is 10x higher above the water than the bottom section. Now add 10 units of lift at the bottom section, and add -1 units of lift at the top section.
Net heeling moment change = 0
Net overall lift change = +9

This is grossly oversimplified since the induced drag will increase, and the profile drag may increase as well, so the boat may end up being slower after the change. But this load-redistribution strategy is effective if done in moderation. The overall optimum load distribution shape depends on many factors, including the fraction of drag from the hull or foils, the effect of boat speed on righting moment, etc. I doubt that the true optimum distribution has reverse loading at the top, but I wouldn't bet against it.

 

[El_Guero]

The real challenge is much more complex. Wind speed above the surface is usually much faster than on the surface.

So, the real challenge is balancing the lift at altitude (usually negative to the rest of the air foil) with the lift generated lower, in much slower, and more turbulent wind.

The 'ideal' mast and sail (or wing) would start 50' above the deck ....



Now you be talking what I love - WIG.

 

[oldsailor7]

Relative to this whole matter of innovation VS status quo, it is interesting to read what Dr Paul Laviolette, a leading astrophysicist has to say:-

"History has shown that the most significant scientific breakthroughs were not deduced from the existing theoretical framework, but rather arose as marked departures from conventional thinking. Generally such new views challenged long-cherished assumptions espoused by the established paradigm and were therefore actively resisted by the old guard.
The peer review process, which normally is relied on to determine which ideas out of the many should become funded, is often subject to this bias. As a result, new ideas that could potentially produce scientific breakthroughs are generally not accepted. Thus most work carried out in today’s research institutions tends to be traditional, rather than innovative."

This retards progress, sometimes for hundreds, even thousands of years.
(Examples---Emperor Tiberius, Aluminium----Ancient Polynesians & Herreshoff-- Catamarans.)

Sounds familiar??

 

[powerabout]

some smart bloke invented it then a university sold a course on it and generated the expert
Education is a business like any other

 

[El_Guero]

Relative to this whole matter of innovation VS status quo, it is interesting to read what Dr Paul Laviolette, a leading astrophysicist has to say:-

"History has shown that the most significant scientific breakthroughs were not deduced from the existing theoretical framework, but rather arose as marked departures from conventional thinking. Generally such new views challenged long-cherished assumptions espoused by the established paradigm and were therefore actively resisted by the old guard.
The peer review process, which normally is relied on to determine which ideas out of the many should become funded, is often subject to this bias. As a result, new ideas that could potentially produce scientific breakthroughs are generally not accepted. Thus most work carried out in today’s research institutions tends to be traditional, rather than innovative."

This retards progress, sometimes for hundreds, even thousands of years.
(Examples---Emperor Tiberius, Aluminium----Ancient Polynesians & Herreshoff-- Catamarans.)

Sounds familiar??

Be careful quoting Scientists who do not support the 'party line.'

I get attacked regularly (on my blog). For some reason, we have moved away from traditional education and skepticism to unbridled enthusiasm for new 'truths.'

 

[oldsailor7]

Yes. Sometimes the pendulum swings too far.

 

[MikeJohns]

Relative to this whole matter of innovation VS status quo, it is interesting to read what Dr Paul Laviolette, a leading astrophysicist has to say:-

"History has shown that the most significant scientific breakthroughs were not deduced from the existing theoretical framework, but rather arose as marked departures from conventional thinking. Generally such new views challenged long-cherished assumptions espoused by the established paradigm and were therefore actively resisted by the old guard.
The peer review process, which normally is relied on to determine which ideas out of the many should become funded, is often subject to this bias. As a result, new ideas that could potentially produce scientific breakthroughs are generally not accepted. Thus most work carried out in today’s research institutions tends to be traditional, rather than innovative."

This retards progress, sometimes for hundreds, even thousands of years.
(Examples---Emperor Tiberius, Aluminium----Ancient Polynesians & Herreshoff-- Catamarans.)

Sounds familiar??

At the end of the 19th century the infatuation with Newtonian Physics held up physics for a bit but not for long. Einstein successfully gave rise to the new physics and since, progress has been nothing short of incredible.
Advancement has always been from the slow and steady distillation of accumulated knowledge and scientific research by specialists in their fields.
But it's in the arena of modern physics and cosmology which is presumably what Laviolette's supposed to be talking about ? Although by all accounts he has some odd ball ideology that's definitely not supported by any science.


In Engineering and Naval Architecture I don't think the concept is applicable. Any proposed significant advancement can and will attract funding from a variety of sources and I'd be interested in examples where you think this was not the case.

That last statement is just plain daft, how could unavailability of funding of a research institution have held up progress for thousands of years?
And what does it have to do with catamarans and Aluminium? Are you trying to suggest that Herreschoff's or the Polynesians catamarans weren't universally adopted, because naval architecture was too stuck in tradition, and no research funding was available for such craft? If so that is incorrect.
It's important to understand that we often need parallel advances before something becomes viable. For Aluminium production for example you need large scale cheap electrical power generation and transmission. For the multihull we require modern materials from plywood on to CF.

 

[dinoa]

The real challenge is much more complex. Wind speed above the surface is usually much faster than on the surface.

So, the real challenge is balancing the lift at altitude (usually negative to the rest of the air foil) with the lift generated lower, in much slower, and more turbulent wind.

The 'ideal' mast and sail (or wing) would start 50' above the deck ....



Now you be talking what I love - WIG.

The ideal mast would telescope. The friction effect of the Earth's surface is pronounced from sea level to 1500m with a larger gradient from surface to 50m. Wind direction also shifts with altitude as surface drag effects geostrophic wind formed by pressure gradient not to mention airmass advection and pseudofronts like sea breezes. Imagine what harvesting a wind shift at altitude would do to upwind performance. Maybe a kite sail on spectra tether.

Dino

 

[high on carbon]

High On Carbon: C-class sailor, wing nut, foiling guy, even when it is physically painful, proud supporter of Leftfield thinking!!!

In my own club, The Royal Canadian Yacht Club, I was subject to years of bias, and outright prejudice against multihulls for starters. Many moons ago I was doing an Olympic Tornado campaign with my brother, and we brought our boat to the club for training. One day I was approached by a very upset commodore who insisted that there was no way in hell a Catamaran could be allowed to stay at the YC and it had to be removed immediately, they were simply not allowed there.

"But commodore" I protested, "The RCYC has a long standing policy that any and all Olympic classes are automatically endorsed fleets of the yacht club and shall be accorded the rights and privileges of other designated classes".

Commodore: "That may be so, but there's no such thing as an Olympic class catamaran, get that thing out of here!"

Now this was around 1988, the Tornado had been part of the Games for some time.

I nodded and smiled and said we would deal with it as soon as possible. Shortly thereafter, I left an article in his mailbox outlining the previous and future Olympics that would feature Tornado's as part of the Olympic sailing discipline. Somehow, the issue was never mentioned again to me.

The next Catamaran to grace our club property was Patient Lady some 16 years later. It too was met with a great deal of scorn, raised eyebrows and suspicion by many of the "established" members. It was interesting to watch the attitudes evolve over time as we developed new boats and went on to be involved in some pretty cool projects. some of the prejudice still persists, but after many years of having an "open tent" policy about our work shed we won people over to the idea that developing new technology does not have to be something that "other people do" nor is it something that "Always happens somewhere else". Many members started paying regular visits to see what they could learn and to show off to their friends the "latest technology in the sport".

So my experience is that for the most part, it is simply a lack of understanding that drives prejudicial thinking. When people do not enjoy firsthand exposure to new things they can be quite skeptical about what it means to them. In sailing I find this to be very true because people have learned a very complicated skill set (Sailing and racing sail boats) over a very long period of time, and something radically new threatens their "expertise" in the discipline. This shakes up the social order of things and they tend to think that their expertise will be diminished and in turn so will their social rank. This is what really threatens people.

I cannot wait to see what will threaten my "expertise" in the future.

 

[michael pierzga]

So ?

My sailing club doesnt allow multihulls. They take up too much space.

 

[El_Guero]

The ideal mast would telescope. The friction effect of the Earth's surface is pronounced from sea level to 1500m with a larger gradient from surface to 50m. Wind direction also shifts with altitude as surface drag effects geostrophic wind formed by pressure gradient not to mention airmass advection and pseudofronts like sea breezes. Imagine what harvesting a wind shift at altitude would do to upwind performance. Maybe a kite sail on spectra tether.

Dino

Kites

:idea: