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

[jmh2002]

Originally Posted by tp12

Regarding the scow bow's wetted area, that's what it looks like, sure, but only if they're perfectly flat.

Some good discussion here:
https://www.boatdesign.net/threads/s...ing-bow.58219/

Yes I understand wide flat bottom boats and have sailed and raced many of them. And yes of course the general idea is should be sailed heeled over to get a lot of that wide flat surface out of the water. This is even very common practice on the modern coastal and ocean racing boats.

Below is a good photo of a scow in this mode (from the thread you linked).



But I'm not sure that an AC75 will be sailed like that? Or will it?

And when an AC75 is foiling they are generally sailed mostly flat, so when they come down off the foils, even if momentarily, AM (American Magic) will quickly have A LOT of wetted surface.

I don't think they will be at an angle of heel like the above photo, although this may change and maybe that will be how they will sail the boat?

I have not yet seen any video of AM going from displacement to foiling. I'm waiting to see this. Do they first heel the boat over to reduce wetted surface, accelerate, start flying, and then come back to flat for stable flight?

Also AM's foils look to be bigger in surface area. I suspect this is to help generate more lift at lower wind and boat speeds to try and overcome their hull's additional drag and fly as soon as possible. But again, it's even more wetted surface area - until the are flying.

These videos of TNZ from page 5 are interesting: http://www.cruisersforum.com/forums/...ml#post2979870

This video at around the 15s mark shows TNZ transitioning on to the foils. They are mostly flat and level.

www.youtube.com/watch?v=elSDgQKvc7I

This video also at around the 15s mark shows TNZ coming down off the foils and sailing in semi-displacement mode. Some are calling this a 'virtual catamaran' - one one foil + the narrow centreline canoe body.

So far TNZ seem to be sailing in a posture similar to the AC 50 catamaran, ie: bow down and a little heel to windward.

https://www.youtube.com/watch?v=Kw5xyAxgrL8

I don't know who is right, or who is wrong, and I suspect the answer may simply be that each boat excels in it's own area, and this may be very dependant on sailing conditions.

I'm looking at it this way - is TNZ's (supposedly) less 'aero' hull 'slower' than AM when flying? Maybe yes (although I haven't seen anything definitive about TNZ's hull actually being less aero, people are just assuming this because it's less rounded)

But then again TNZ also appears to have (at least so far) smaller surface area foils compared to AM. These will be less drag and therefore faster once up and flying, perhaps making up for the (supposedly) less aero hull?

Certainly though it appears that TNZ is able to 'touch down' or perform a 'touch and go' with much less wetted surface immersion than American Magic, and is in fact even designed to sail in this mode if and when necessary.

It's fascinating

[tp12]

I'd imagine that they'll have different design characteristics based on their own assumptions, how they plan on sailing them and, being brand new designs, there'll be trial and error, mistakes and successes. Validating/testing these should all inform the design of the second hull, too, I'd hope. Depending on what constraints they have, too.

I agree, it's definitely exciting and I can't wait to see more action.

We might see a few head scratching moments but it's good to see different design approaches to make things interesting.

Game on!

[MicHughV]

there are foils...and there are foils....
the a/c boats don't generally sail in rough seas....but the Imoca class does...and they are also foilers, but seems like a different type....not to mention a huge disparity in crew.

I tend to agree with the many thoughts here that there will likely be a long on-the-water learning curve here as teams figure out what clicks and what does not...and hopefully some of this will be shared with the general viewership as these events unfold...

...was watching some video of "Hugo Boss" racing against two kite foiling boards, very different foiling designs...interesting stuff....

[a64pilot]

So the rules allow “flight controls” on the foils? High lift devices, like flaps?

[a64pilot]

Originally Posted by StuM

If the designers are smart, the hulls will also provide aerodynamic lift, stability and "ground effect" lift.

I’m seeing that in the US boat, but not the others, the bump on the bottom of the boat, which I’m calling a release step cause that is what it is, adds aerodynamic drag and will to a great extent spoil the airfoil that the fuselage, excuse me, hull is.

[cpisz]

I have read that the foils are swappable. So the fact that one boat currently has different size foils is not that important. They will tune them to the perfect size.

[jmh2002]

Originally Posted by jmh2002

Small update: https://www.sailingscuttlebutt.com/2...omes-fuselage/

So we will see different foil designs emerge over time

^^^^^

[a64pilot]

I wonder what is meant by foil flap?

[jmh2002]

Originally Posted by a64pilot

I wonder what is meant by foil flap?

The AC75 Class Rules are available for download from the official site here: https://www.americascup.com/en/official/the-class-rule

Page 23, Section 13, Foils

13.1 Each foil must comprise:
(a) a foil arm and a foil wing, which must form a single linear component;
(b) two foil flaps, each of which must be a linear component; and
(c) one or more foil systems.

Page 24, Section 14, Foil Arms

14.2 Each foil arm shall only be constructed from:
(a) one foil arm stock; and
(b) one foil arm fairing.

Page 25, Section 15, Foil Flaps

15.1 A foil flap must be a linear component connected to a foil wing by a foil system.
15.2 Each foil shall include two foil flaps, one lying entirely on one side of the foil wing symmetry plane, and one lying entirely on the other side of the foil wing symmetry plane.

In basic terms, as I understand it:

- Stock Foil Arms are supplied to all teams
- Teams fit a Fairing of their own design to the stock Foil Arms
- Teams fit Wings of their own design
- Teams fit (adjustable) Flaps of their own design to these wings

So the design is the same basic principle as an aircraft with a Wing and a Flap.

There is also a drawing that indicates box rule dimensions that the Team designed parts must fit within.

Page 24, Figure 13.1, Foil Geometry

Page 27, Section 16, Rudder

16.6 Only the following rudder movements are permitted relative to the AC75 yacht:
(a) yaw, being a rotation about an axis joining the lower and upper bearing centres; and
(b) rake, being a rotation about a transverse axis through the lower bearing centre.

In basic terms, as I understand it:

- The Rudder has a Wing but it is not adjustable.
- Instead the Rake of the Rudder can be adjusted from inside the boat.

Clear as mud?

[MicHughV]

...I would tend to think that the Kiwi's...when faced with this decision...
..a) crew comfort
..b) an extra 0.001 knot of speed
would opt for (b)...not sure about the other competitors....y'know, the Brits wouldn't design anything that might spill their gin and tonic...haha...ok, that was supposed to be a funny.

The past a/c catamarans had little in the way of crew comfort or safety.....crew were bouncing over springy trampolines and practically diving into the windward ama...you might recall back in 2013 an a/c sailor lost his life.....

the physical strength and level of fitness of these crews must be taken into account when racing these boats...it's not a game for arm-chair sailors, that is for sure......these a/c 75 footers will likely be pressed to a razor sharp intensity....the loads on the mast, rigging, sails, foils, etc, will be intense...especially clipping along at 50 knots or so...one screw up anywhere and you've lost that race..

[jmh2002]

It's not so much 'crew comfort' as in luxuries or niceties.

The thing with these AC75s is that crew comfort understood in terms of safety, or in terms of being able to operate the yacht more efficiently, are not necessarily mutually exclusive.

Having the crew set deeper down in the boat on TNZ seems to met those goals, as well as keeping the weight low and reducing the aerodynamic drag too.

A win-win hopefully.

[CassidyNZ]

Originally Posted by MicHughV

...I would tend to think that the Kiwi's...when faced with this decision...
..a) crew comfort
..b) an extra 0.001 knot of speed
would opt for (b)

But if you can get an extra 0.001kn of speed as a direct consequence of getting some crew comfort, that’s got to be a win. Fact is that the gains from an aerodynamically perfect hull are quickly squandered by having a gang of people standing up in a substantial airflow, grinding on pedestals.

[MicHughV]

Some points to ponder:

Crew location and hull protrusions becomes a factor at high speeds, given that the generally accepted rule is that force goes up as the square of wind speed.

For most sailors bopping around the ocean at 6-8 knots.....this is usually never an issue...but clipping along at 50 knots equates to sailing in a Force 9 gale plus...so I can see where some serious thought must be given to crew location/protection, etc...

Few (if any) of us have sailed at 50 knots or anywhere close to that speed, though many sailors have likely had to weather 50 knots or more of bad weather..by which point most of us are hunkered down with storm sails.

While we are hunkered down behind a storm trysail, the a/c boats will be clipping along at sustained speeds north of 40 knots...and ostensible having fun doing so...

For a personal comparison, in my misspent youth, I used to ride a Harley. It came equipped with a large windshield that could be detached. Riding without that windshield was never very pleasant and I quickly learned to appreciate that big slab of acrylic in front of me.

In the same way, the a/c designers must have thought this condition thru' themselves and have come up with their own solutions to the problem.

We will see soon enuff as these boats get put thru' their paces

[Tillsbury]

Originally Posted by CassidyNZ

- INEOS - beam on protection for those rare moments when wind will come from the beam,

If the wind is from the beam, they’ve already lost. These boats only ever go upwind. The 50+kts in the faces of the crew are going to be significant, and with the inevitable spray on top it’s not just “uncomfortable”, it will seriously affect their ability to sail the boat. imho. I’d be surprised if boat 2 from each syndicate doesn’t maximise crew protection.

[jmh2002]

TNZ were testing their Code Zero today, in light air, in semi-displacement mode.

America's Cup: Emirates Team New Zealand flies Code Zero:

https://www.sail-world.com/news/2228...the-first-time