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

[MicHughV]

Regarding foils....

My first boat was equipped with a " Monitor" self-steering gear.
This Monitor had a symmetrical foil/rudder in the water at the end of an arm.
I would guess the actual foil being about 24" long and probably around 4" wide, as measured along the chord, not very wide at all. This would be the immersed part.
This blade/foil/servo rudder was rotated to port or starboard as directed by the wind vane above it. As the immersed blade rotated it would want to swing to the left or right and in the process pull a rope which was attached to small drum on your main steering wheel.

On an ocean passage I has ample time to study this device and often did as there was not much else to do.
This foil was probably able to turn 15 degrees to the left or right, but it that depended on the wind speed and boat speed. Most of the time, it kinda just flipped flopped from one side to the other in a relatively tight arc, keeping the boat on track. Being able to look right down on top of the blade, one could immediately see the water swirling around the blade, even at very low speed, as the blade was generating its own low pressure/high pressure sides, as it tried to turn left or right...ok...port and starboard

At a cruising speed of around 6-7 knots, that little immersed blade could exert a force out of context with it's size. At a rough guess, maybe 50 lbs.

I've seen other self-steering gear which employs a small trim tab attached to the rear of the rudder. Again, a small turn of this tiny blade, could be readily translated into a very strong force, sufficient to turn the rudder.

The AC boats off course sport massive foils, those foils are either symmetrical and canted to the surface a tad or are otherwise shaped as a airplane foil to generate lift sufficient to raise the entire boat out of the water, but there is no way in hell, the stem of these foils are moving thru' the water, parallel with the centerline of the boat when it's moving, or.......maybe they are.... maybe they have a slight twist or " toe-in" that we can't see from photo's, that would allow for the stem of the foil to track perpendicular to the center line of the boat when it's moving.. At 50 knots, this " twist" would need to be only incremental, something that would not be noticeable by eye. Maybe the spray we see is the sideways component of the wind load as the boat is being pushed off to leeward.

I just throw this out, knowing that a foil not aligned with the water flow can exert a force out of context with it's size. There must be something going on with these AC75 foils that is not apparent to the casual viewer.

I invite comment.

[jmh2002]

Here is an interesting interview with INEOS Team UK Head of Design Nick Holroyd:

https://www.sailweb.co.uk/2019/10/08...he-ac75-boats/

I have quoted some excerpts:

The Kiwis still have an advantage here, do you think?

I was involved with some the development with the Kiwis last time so, yes, they came into this Cup cycle with a more mature set of tools, they did a lot of simulation through the last campaign and that stood them in good stead.

Foils? Where are you in terms of size and shape compared with the ‘fleet’?

Ourselves and the Kiwis have built different foils for different sides of the boat. American Magic seem to have a very similar foil on both sides of the boat. Likewise Luna Rossa although I think their actuation mechanism is different port to starboard. That has been a huge amount of hard work because you double up your engineering, because everything that goes inside there is custom. Our smallest foil is about as small as anyone in the fleet, down there with Luna Rossa in that sense and our bigger foil would be roughly midfleet – compared with Team New Zealand in terms of area.

Your thoughts on the three boats which have been launched?

Everybody is pushing. Really pushing. There are a lot of ideas, quite new and novel ideas. It is very hard to go past the Team New Zealand boat for two reasons. There are few bits of information to which we are not privy to, like the wind limits might be etc., and two, we had five months from class rule to launching boat 1, they undoubtedly had this concept in their simulator a lot longer than that, I was taking to them in October the year before so they probably had six months more.

The bustle on the Kiwi boat?

It is very smart. Theirs is a very clever boat.

Does it worry you?

...They have had longer and know the conditions. I would pick their boat as one which has to some extent disregarded any floating races...

...American Magic is probably closest to us in terms of a boat which will perform well in the floating condition. It is a nice boat, very well executed and they are on the water early and learning. It is a good programme...

...Luna Rossa is quite an extreme boat, their foils are very, very small. There is learning for us to take from them...

Will your second boat more radical?

It will be different . . . even if you think you are right you would not build another one the same. I am not arrogant enough to think I am right. And there is a lot to learn from other people, to put resource into different places in the design cycle.

The most interesting two comments above (at least for me), apart from the fact that he thinks TNZ's boat is "very smart, very clever", are that he thinks that Team UK and AM will perform well in "floating conditions" (which will be light air).

I guess that is because in basic terms Team UK and AM appear to have more initial form stability with their flatter bottom hull shapes.

However I still they will be high wetted surface and high drag when immersed.

And his comments don't seem to include TNZ's ability to sail in 'semi-floating' mode, which might be a game changer.

It would appear that 'they didn't think of that' design option.

[cal40john]

Originally Posted by a64pilot

Well something has to be resisting the lateral force, and lift is generated 90 degrees to an airfoil, that is why an airplane is banked to turn, so either the lifting foil is banked or something else is countering the down wind drift.
Normal sailboats with a keel counter it by steering into the wind thereby causing the symmetrical keel to produce lift, whether it has an airfoil section or not.

Maybe they will tilt to windward like the Moths do turning some of the vertical lift into horizontal lift.
Top picture of Moths going to windward -
Foiling History – UK International Moth Site

[a64pilot]

Seeing as how controllable high lift devices are allowed and size of the foils isn’t apparently limited, and I’d assume they are allowed to change foils, I’m not so sure that there will even be much sailing with the hull in contact with the water.
Time will tell of course.

The bustle or I still call it a release step will generate both negative lift when flying and drag of course, so it’s not design without negatives, all designs will give up something of course.

I wonder if a moveable tab like a trim tab on the hull bottom would have been allowed?

[a64pilot]

Originally Posted by cal40john

Maybe they will tilt to windward like the Moths do turning some of the vertical lift into horizontal lift.

Top picture of Moths going to windward -

Foiling History – UK International Moth Site

They may heel or bank if you will seeing as how they fly.
I’m still not discounting the force from the strut, think how small one foil is, and it supplies enough lift to fly the boat, and with controllable high lift devices they can control the height at which they fly, and by doing that control the horizontal lift the strut can produce.

All this is just theorizing of course, but it would seem that they have a whole lot more to think about than just sailing, someone has to fly the thing. I wonder if that is a full time job or just a side job for someone, maybe the helmsman?

[jmh2002]

Originally Posted by cal40john

Maybe they will tilt to windward like the Moths do turning some of the vertical lift into horizontal lift.
Top picture of Moths going to windward -
Foiling History – UK International Moth Site

From earlier in the thread:
http://www.cruisersforum.com/forums/...ml#post2979870

Originally Posted by jmh2002

Here is the slightly better video of TNZ...

And some comment from Sail World:

https://www.sail-world.com/news/222183/?source=rss

[Pelagic]

Originally Posted by jmh2002

Luna Rossa is up and flying:

https://www.sailweb.co.uk/2019/10/20...f-their-speed/

Nice looking boat

[jmh2002]

Originally Posted by a64pilot

Seeing as how controllable high lift devices are allowed and size of the foils isn’t apparently limited, and I’d assume they are allowed to change foils, I’m not so sure that there will even be much sailing with the hull in contact with the water.
Time will tell of course.

The foil size is limited within a box rule. Please see my very detailed posted here: http://www.cruisersforum.com/forums/...ml#post2991797

[jmh2002]

Originally Posted by a64pilot

...it would seem that they have a whole lot more to think about than just sailing, someone has to fly the thing. I wonder if that is a full time job or just a side job for someone, maybe the helmsman?

Agreed. On the AC50 catamarans there were manual twist grips on the helm wheel of most boats and the helmsman was in control of both steering and flying.

Except for TNZ who took a different approach. Because TNZ's design utilised 'cyclors' instead of 'grinders' they tasked a separate crew member to fly the boat.

This crew member spent most of their time head down staring at and controlling a flight horizon type device.

But this approach allowed TNZ to use foils with less area, and less drag, so faster and operable across a wider wind range, yet still have better control of flight than the other boats.

I believe that a similar setup is now standard on the SailGP catamarans.

So, Airbus has quite some competition to deal with in the form of TNZ

[jmh2002]

Originally Posted by Pelagic

Nice looking boat

Very

And interesting that so far this is actually being considered the more radical and/or aggressive design.

[CassidyNZ]

Originally Posted by cal40john

You stated that you know what is required to produce lift

Really? Where?

[cal40john]

Originally Posted by CassidyNZ

Really? Where?

The next line in italics that you left out of your reply was a quote from your post.

[wingssail]

Originally Posted by a64pilot

Well something has to be resisting the lateral force, and lift is generated 90 degrees to an airfoil, that is why an airplane is banked to turn, so either the lifting foil is banked or something else is countering the down wind drift.
Normal sailboats with a keel counter it by steering into the wind thereby causing the symmetrical keel to produce lift, whether it has an airfoil section or not.

YES, You have it! The lifting foil is banked!

[a64pilot]

Originally Posted by wingssail

YES, You have it! The lifting foil is banked!

Is it? If so then I would assume they can trim the amount the leg is deployed, raise it a little and increase the bank angle and therefore the side force, lower it and decrease it?
Many ways to skin a cat, I wonder which they do, or all?
Is any of this allowed to be electronically controlled, as in software?

[wingssail]

Originally Posted by a64pilot

Is it? If so then I would assume they can trim the amount the leg is deployed, raise it a little and increase the bank angle and therefore the side force, lower it and decrease it?
Many ways to skin a cat, I wonder which they do, or all?
Is any of this allowed to be electronically controlled, as in software?

The arm "cants", meaning it rotates about the canting axis. Full cant and the arm is vertical and the foil (wing) is beyond horizontal (see image). You don't expect to see this position in use.

As the arm rotates out of the water the foil becomes first horizontal, producing only vertical lift, then angled (or banked) producing both vertical and horizontal components. (see post #170). The cant is controlled by an operator on the vessel.

There are no moving parts allowed on the foil arm itself. It is symmetrical. I do not find any reference to toe-in or angle of incident in the rule. So the only lateral force created by the foil arm would have to be produced by angling (crabbing) the whole boat.

The foil itself is allowed to have "foil flaps' which control or change the lift produced by the foil. These too are controlled by an operator on the vessel.

Automatic control (by software) of the position of all movable controls is not allowed, only human control however some "force feedback" is allowed (meaning the operator sets the force he wants and the control system maintains that force, not just the position).