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

[Tillsbury]

What I meant was that "displacement" simply isn't going to be a part of any race. There may be time when they stuff up, and have to get out of the water as fast as possible. But I'm guessing they'll want to be foiling close to 100% of the race.

[Pelagic]

Originally Posted by jmh2002

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:



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.

My thoughts exactly but also I think Structurally TNZ's hull is superior in shape if execution is equal.

These boats are going to be stepping down into waves and swell at high speeds. Somewhat akin to falling off a wave at sea when going too fast.

TNZ will have a much gentler entry, stepping down and the better ship shape will initially help to stabilize rather than have a corner dig in.

This will be a fascinating learning curve for sailboat designers and sailors worldwide.

Acceleration should also be in favor of TNZ as the asymmetrical leading edge of the bow reminds me of a float planes pontoon which is designed to reduce water suction on takeoff.

However, there are so many variable hard to tell until tested in all conditions and I think the 2nd boats will all be more similar based on the best ideas tested

[Tillsbury]

Also remember that there's usually some decent chop outside the harbour, so these boats are going to have to be able to handle waves hitting the hull at speed when foiling in decent wind. That'll be interesting. This is not a flat water course.

[jmh2002]

Originally Posted by Tillsbury

What I meant was that "displacement" simply isn't going to be a part of any race. There may be time when they stuff up, and have to get out of the water as fast as possible. But I'm guessing they'll want to be foiling close to 100% of the race.

I get your point but not the wording. Of course they are not expected to sail around the whole course in full displacement traditional monohull mode.

But it's also why I introduced 'semi-displacement' to better describe these "not-slow, not-fast times" suggested by designer Dan Bernasconi...

In fact as you mean, now we are at the point where 100% foiling is expected, but this also means that anytime you are not foiling for whatever reason the boat is incredibly slow by comparison.

Take a look at the SailGP races and you still regularly see dips off the foils even during straight line sailing.

I think part of the reason for this is that SailGP is racing in different venues and weather and sea conditions, not the mostly flat water of Great Sound in Bermuda.

As you are aware there will also be much more variable wind and sea conditions in the Hauraki Gulf and TNZ obviously think that this justifies a completely different boat design to the norm to try and mitigate and shorten any non foiling period.

TNZ will try to do this by sailing in this 'semi-displacement mode' up on this centerline canoe body part of the hull. It may only be for a number of seconds, but drag will already be reduced and they will already be going faster.

American Magic will have to use the technique of any wide flat mono hull, and that is to get heeled over and get those big flat sections out of the water.

This won't work with a 'touch and go' dip during straight line sailing though - there will be A LOT of flat surface immersed very quickly, and this will be very slow. In this regard I think the TNZ design is very clever - if it works they may get away with only dipping this slim canoe body and then bumping themselves back to fully foiling.

You can also see that American Magic's foil arm fairings are much fatter, and the foil wings look shorter and fatter too. I could be wrong but normally this means they are trying to make more lift at low speed (even when the foil arm is in the water) but at the expense of more drag.

And this makes sense because they need this lift to overcome the drag of that big flat hull.

TNZ appears to be the opposite. Slim foil arm fairings, and long slim foil wings. Less drag, so (in theory) faster, but also less lift in the first place. But then (in theory) they don't need as much lift because they can first transition to semi-displacement mode on the canoe body, reduce hull drag, and then fully foil. This may only take seconds of course, but seconds add up, and seconds win races.

Once up and foiling TNZ's 'smaller' foils are normally the faster design.

That's how I see it anyway.

There really are two very different schools of design thought between the two boats. It's very interesting.

[jmh2002]

Originally Posted by Pelagic

My thoughts exactly but also I think Structurally TNZ's hull is superior in shape if execution is equal.

These boats are going to be stepping down into waves and swell at high speeds. Somewhat akin to falling off a wave at sea when going too fast.

TNZ will have a much gentler entry, stepping down and the better ship shape will initially help to stabilize rather than have a corner dig in.

Yes, flat boats pound like crazy in waves.

I think TNZ's plan is to try and land on this centreline canoe body during a step down off a wave, add a bit of buoyancy without adding too much drag, and then pop up again.

The boat is not form stable on the canoe body section, it is way too small, that is what the main hull is for. The canoe body is a low drag hull section for these transitions.

Hence my original 2 hulls in 1 comment.

[svenskflicka]

Once again TNZ's foils look more fancy pants than USA....

[jmh2002]

This video and my comment is a bit unfair, since they have only just started sailing the boat, but it is an example of all that flat surface producing a huge amount of drag as soon as the hull even just kisses the water. Boat looks good up on the foils though.

But nobody is a fool on the American Magic team and this is pretty basic stuff so they will be well aware and they must think the trade off is worth it for other advantages.

And maybe the TNZ design will be a failure. These are all Boat #1s, and we haven't seen the Italian or the United Kingdom boats yet. Still TNZ have a track record of thinking outside the box, and being fast, and maybe the other teams are already thinking 'holy shxt' we have got this totally wrong'.



American Magic: Foiling, Gybing, and Parking...

https://www.youtube.com/watch?v=SMuEXw6WaUY

[Pelagic]

Originally Posted by jmh2002

This video and my comment is a bit unfair, since they have only just started sailing the boat, but it is an example of all that flat surface producing a huge amount of drag as soon as the hull even just kisses the water. Boat looks good up on the foils though.

But nobody is a fool on the American Magic team and this is pretty basic stuff so they will be well aware and they must think the trade off is worth it for other advantages.

And maybe the TNZ design will be a failure. These are all Boat #1s, and we haven't seen the Italian or the United Kingdom boats yet. Still TNZ have a track record of thinking outside the box, and being fast, and maybe the other teams are already thinking 'holy shxt' we have got this totally wrong'.



American Magic: Foiling, Gybing, and Parking...

Has anyone read a weight comparison , between the two boats?

Ironically those chase boats are going to burn a lot of fuel keeping up with the sailboats

[jmh2002]

Originally Posted by Pelagic

Has anyone read a weight comparison , between the two boats?

No, and I don't think anyone is going to disclose their actual weights at this point. No way. Some weights do however form part of the box rule.

[CassidyNZ]

Originally Posted by Pelagic

Has anyone read a weight comparison , between the two boats?

Ironically those chase boats are going to burn a lot of fuel keeping up with the sailboats

Don’t know if you’ve seen ETNZ’s chase boat? 4 off 400hp Mercury outboards on one boat! 1600hp. On a chase boat.

[CassidyNZ]

Am I mistaken in thinking that the foil arms on all boats come from the same manufacturer? There are several comments on the differences between ETNZ and NYYC foil arms.

I believe only the actual foils are down to individual design.

[jmh2002]

Originally Posted by CassidyNZ

Am I mistaken in thinking that the foil arms on all boats come from the same manufacturer? There are several comments on the differences between ETNZ and NYYC foil arms.

I believe only the actual foils are down to individual design.

The Foil Arms are one design and supplied equipment, but open design Foil Fairings can be fitted over the Foil Arms. The Foil Wings are totally open design but within dimension restrictions.

https://www.sail-world.com/news/2220...sailing-images

"The most significant point of difference between the foils on the two AC75's launched to date, aside from the differences in hull design, is the approach with the foil fairing and foil wing. While the carbon foil arm is one design and a supplied part, the teams are free to add whatever fairing they wish. With the foil wing, it must fit within six-sided template outline, otherwise it is free design. The foil wing is allowed to weigh up to 740kg, and when not being used as a foil is canted to windward to provide righting moment."

[cj88]

First sail.

[jmh2002]

Yes, a full article is here, not a lot of detail but some photos: https://www.stuff.co.nz/sport/americ...sting-new-boat

In the photo above from cj88 the deck sweeping mainsail (for end plate effect) is clear to see.

And the crew do indeed look lower in the TNZ boat than in American Magic. It's noticeable that the helm wheels are below the sheerline on TNZ but above it on American Magic.

If I understand correctly, due to the deck sweeper mainsail and the aero hump in the cockpit, the grinders, etc on TNZ will not change sides during each tack and instead stay down in the pit for reduced windage. I suppose they are considering this trade off vs the weight transfer, which may now be less important when foiling in level flight?



American Magic:



Team New Zealand:

[CassidyNZ]

The deeper crew wells on ETNZ’s boat not only reduces aerodynamic drag but also reduces fatigue. Sitting in 50kn of wind will get quite tiring quite quickly.

In a video online today the bulge under the boat started to show perhaps why it’s there - the boat sank on its foils momentarily and the bulge kissed off the surface and went straight back up again.

Interesting “pocket” in the leach of the mainsail. Wonder what that’s all about? Looks like it goes quite a long way up.