America’s Cup - ETNZ launches 1st AC75 (new)

[jmh2002]

But as we see from the photo I posted earlier as well as video of American Magic's half scale test mule the AC75 sails fully airborne and almost level.

TNZ chose not to build a test boat and instead do design and crew work experimentation via simulators, which are now incredibly advanced for high performance sailing. This not only saves time and money, but I suspect is also used from a design secrecy point of view to try and get a jump on the competition.

Also you can see that aerodynamics are becoming a major consideration and the crew, particularly the grinders, sit below the foredeck level. This is especially pronounced on TNZ's boat.

Just like the AC50 foiling catamarans (or almost any foiling design) there will however be a 'transition period' between displacement and flying modes.

American Magic's hull is totally flat underwater, whereas Team New Zealand's has an unusual (and unexpected) bulb like bulge on the centreline of the hull.

NB: These are boat number 1. The rule permits a maximum of two boats, so there will be design evolutions for boat number 2. The foil arm package is standard and supplied to all teams.

Hope this helps with some technical understanding

Originally Posted by www.thespinoff.co.nz

https://thespinoff.co.nz/sports/06-0...-boat-te-aihe/

Most surprising of all is a sort of bulge running the length of the bilge, a bilge bulge, like an undercarriage...

Being a lot heavier than the catamarans of the previous America’s Cup, it’s a harder boat to get onto its foils. So – as I understand it – the dolphin belly serves as a kind of smaller, secondary hull, minimising drag in that awkward phase between foiling and not foiling.

During those not-slow, not-fast times, “it’ll only be that bit in the water, and that part is far more like a multihull shape”, said designer Dan Bernasconi...

American Magic, flat hull, level flight:



American Magic, test mule sailing:

https://www.youtube.com/watch?v=eTVKkv9xtAo

Team New Zealand underwater hull bulge:

[a64pilot]

Perhaps the bulge acts as a form of release step.
Aircraft floats have these as without them at speed the floats will actually form a suction to the water that is hard to overcome, and of course for the airplane to fly it has to come out of the water.
I’m surprised these boats don’t have a form of “step” for the same reason.

[jmh2002]

Originally Posted by a64pilot

Perhaps the bulge acts as a form of release step.
Aircraft floats have these as without them at speed the floats will actually form a suction to the water that is hard to overcome, and of course for the airplane to fly it has to come out of the water. I’m surprised these boats don’t have a form of “step” for the same reason.

Ah, that's a very interesting example from another field, thanks

[a64pilot]

I’m thinking that, or perhaps in a turn etc when it may come down off of the foils some and the hull begins to contact the water, drag could rise very high, perhaps the bump serves to keep the whole hull from being wetted? Or it could be to reduce aerodynamic drag?

Or maybe it has no function, was put there to drive theorist nuts

Look up a Gurney flap to see how a very functional genius bit of aerodynamics was successfully camouflaged in plain sight.

I can see how these things could be FAST as I would assume it’s easier to make a low drag monohull as opposed to a multi when they are foiling.

[Pelagic]

I feel sorry for the fishes in the sea

[jmh2002]

Originally Posted by a64pilot

I’m thinking that, or perhaps in a turn etc when it may come down off of the foils some and the hull begins to contact the water, drag could rise very high, perhaps the bump serves to keep the whole hull from being wetted?

Yes, as quoted earlier: "During those not-slow, not-fast times, “it’ll only be that bit in the water, and that part is far more like a multihull shape”, said designer Dan Bernasconi..."

Originally Posted by a64pilot

Or maybe it has no function, was put there to drive theorist nuts

It's still the America's Cup so anything is possible

Originally Posted by a64pilot

I can see how these things could be FAST as I would assume it’s easier to make a low drag monohull as opposed to a multi when they are foiling.

Everyone seems pretty confident that the AC75 monohull will sail in excess of 50kn.

The AC50 catamarans from the last Cup, having been standardised and improved, are now regularly exceeding 50kn in the right conditions on the SailGP circuit.

I've sailed monos and multis in the mid 20kn - it feels very fast. And I've run high speed motoryachts regularly at 40kn to 50kn+ and it feels blazing fast. Almost unbelievably so. Even just the apparent wind pressure starts to feel immense at those speeds.

So 50kn and up in the air on the foils, totally exposed, that is quite something.

But I will add one point, just like fast cars (or aeroplanes I guess too?), you get used to the speed very quickly. On the big fast motoryacht, sometimes we would slow right down for comfort in a bumpy sea - and still be doing 33kn! Completely outrageous

[jmh2002]

Here is some new footage of American Magic sailing their AC75:

NYYC American Magic AC75 Boat #1 Testing

https://www.youtube.com/watch?v=-43qV_U9biY

[jmh2002]

American Magic has officially launched and names their boat "Defiant".

https://www.sailingscuttlebutt.com/2...lo-to-defiant/

Launch party video but also includes some much better sailing footage.

https://www.youtube.com/watch?v=d4QAdota91Q

[barnakiel]

Her awesomeness !!!


What a show. I am considering visiting Auck to watch the finals live.



b.

[jmh2002]

It appears that Team New Zealand and American Magic have each taken a very different design approach. The boats are each a totally different concept with some large specific differences.

American Magic is a very flat Scow type design whereas TNZ seems to be more of a hybrid between a wedge and a canoe body hull.

It might be an illusion but TNZ seems to be a taller hull overall and seems to sit the crew lower in the hull for less windage (just guesstimating this from comparing the wheel heights and grinder positions in the cockpit). But let's see more when TNZ goes sailing.

American Magic also has radically different foil arms and foil wings by comparison, even including a torpedo bulb. They are assumed to have their own advantages of course but these foils look like they have much higher drag and windage compared to TNZ?

I might be wrong but it seems to me that American Magic is more focused on performance in specific conditions, whereas TNZ seems to include design aspects to perform in variable conditions?


Here is a very good article discussing some of the differences and with a lot of photos and more video too.

America's Cup: Images and video reveal American Magic's novel design approach
https://www.sail-world.com/news/2220...sailing-images

This article also mentions that "the rigs also will be quite different, with American Magic opting for a conservative rig, while the Kiwis are expected to unveil a deck sweeper mainsail, without a convention main boom and sheeting."

[jmh2002]

More info:

"America's Cup: The first week - two very different AC75's compared"

https://www.sail-world.com/news/2220...AC75s-launched

[Tillsbury]

It's going to be a lot of fun. Great to see that the boats will actually sail as per the original animations! I'm sure a fair number of people doubted they would ever be able to do that at all.

I understand that the simulations that TNZ have been running have led them to take a great deal of notice of the aerodynamics of the boat overall, more like an aeroplane than a boat. On the other hand, since American Magic has Airbus on board I doubt they'll be short of expertise in that department, should they wish to go looking...

[jmh2002]

Here are a few more photos.

American Magic's very convential and flat underwater shape:



TNZ's very UNconventional and NOT flat underwater shape. Finally in this photo it's very clear that TNZ's hull is trying to be "2 boats in 1" to assist in the transition from displacement to foiling:



And here some more comparison of the cockpit differences. TNZ is suspected to have a deck sweeping boomless mainsail which will meet the cockpit to produce an end plate effect.

[Tillsbury]

It's not "two boats in one". It's an aircraft most of the time. The rest of the time it's a boat trying to get out of the water. How it handles displacement sailing is pretty much irrelevant, as ideally it'll never be doing that. The hull's only job is to get the boat foiling. Once there, the hull needs to be as aerodynamic as possible. It'll be interesting to see how much ground effect makes a difference between the boats.

It does look clearly like the Americans have made a traditional boat with foiling arms (a big version of what they did with the mule), but TNZ have started with a much more blank slate doing it all via simulation.

[jmh2002]

Originally Posted by Tillsbury

It's not "two boats in one". It's an aircraft most of the time. The rest of the time it's a boat trying to get out of the water. How it handles displacement sailing is pretty much irrelevant, as ideally it'll never be doing that.

I have to disagree. Based on TNZ's hull design they appear to think that 'how it handles displacement (or semi-displacement) sailing' actually might be very relevant - even if it is relatively momentarily, ie: during lower speed maneuvers, and during the transition from displacement to foiling (and back again, eg: during a dip or crash)

See the quote earlier from the designer of TNZ Dan Bernasconi:

Originally Posted by www.thespinoff.co.nz

Being a lot heavier than the catamarans of the previous America’s Cup, it’s a harder boat to get onto its foils. So – as I understand it – the dolphin belly serves as a kind of smaller, secondary hull, minimising drag in that awkward phase between foiling and not foiling.

During those not-slow, not-fast times, “it’ll only be that bit in the water, and that part is far more like a multihull shape”, said designer Dan Bernasconi...

We saw the the AC50 catamarans were enormously slower (of course) when they came off the foils and immersed the hulls, even momentarily during flight. Boat lengths were lost just from a little dip.

One downside to American Magic's design is that as soon as they have any immersion of the hull, for whatever reason, it will immediately be a lot of large flat surface area in the water and a significant amount of increased drag.

It seems that TNZ are trying to mitigate that type of situation with a 'mini hull' which will add some buoyancy to help towards getting up (or back up) onto the foils but with much less drag than (and hopefully at times even preventing) full immersion the main hull.

TNZ's hull clearly has 3 possible modes: displacement, short term semi-displacement, and foiling.

This is what I meant by '2 hulls in 1'.

Now let's see of that idea actually works.