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

[jmh2002]

Some more sailing footage from TNZ:

https://www.youtube.com/watch?v=7EqKjZgPv34

[MicHughV]

I'm no foil expert, but it would seem these AC75's do better with both foils immersed. Those are big boats to be leaning on only one foil...and that other foil sticking up in the air like that has got to compromise airflow to the sails plus have it's own wind resistance....
With only the small foil on the rudder these boats seem to be nose heavy to my eye.
Both foils are in the water from time to time anyway during maneuvers or even low wind condition....and perhaps having two foils in the water may require less effort to get airborne.
For a point to ponder after watching this, I'd be inclined to go back to the computer and re-design this boat with both foils in the water...but smaller foils on either side..???
The non-immersed foil must act as supplemental " ballast"..is the only reason I can think off to keep it out of the water.
But I will add again, I'm no foil expert.

[jmh2002]

Respectfully and politely I think that it would be helpful for your understanding to go through and read the previous posts in this thread, particularly if as you say you are not 'an expert' since many of these points have been addressed, some with much technical detail.

Originally Posted by MicHughV

I'm no foil expert, but it would seem these AC75's do better with both foils immersed. Those are big boats to be leaning on only one foil...

In certain wind conditions that may well be the case, and also may well be part of the reason for TNZ's centre line canoe body which appears to enable partial foiling. Foil sizes and shapes can be changed too.

Originally Posted by MicHughV

...and that other foil sticking up in the air like that has got to compromise airflow to the sails plus have it's own wind resistance...

Some aerodynamic drag yes, but I'm not sure about airflow to the sails. The apparent wind will always be forward of the beam on these boats.

Originally Posted by MicHughV

With only the small foil on the rudder these boats seem to be nose heavy to my eye.

Nose down and some windward heel is the fastest trim.

Originally Posted by MicHughV

For a point to ponder after watching this, I'd be inclined to go back to the computer and re-design this boat with both foils in the water...but smaller foils on either side..???

The non-immersed foil must act as supplemental " ballast"..is the only reason I can think off to keep it out of the water. But I will add again, I'm no foil expert

Where would the righting moment come from with your re-design? Sorry but that doesn't really make sense.

The foils are ballasted. Also consider that the effect of this ballast is multiplied by being many meters away from the centre line.

Additionally the whole point is that the design is adjustable for different conditions.

The extra hydrodynamic drag by having both foils immersed is significant.
The AC50 / SailGP catamarans also retract the windward foil when it's not required.

Water is much denser than air and creates much more drag.
Adding more immersed parts defeats the whole point of a design like this.

Also remember that these are training videos and the crew are still learning to sail the new design and will be constantly experimenting with everything.

So what you see will surely not be their very best effort.

In fact quite the opposite, at times they will be trying to purposely hide some aspects from the other teams.

[MicHughV]

As an avid sailor for most of my life I take a keen interest in sailboat design.

I have read every technical and commentary post here, but have come to the conclusion that this is a new playing field for all and certainly nobody knows all the answers and contrary to your own belief, I suspect neither do you.

I posted an opinion, certainly within my rights to do so, and not a fact, based on a video I saw, and I see plenty of room for refinement here.

Since the old style 12M AC boats, virtually every new AC race has sported some or other new design or feature and this upcoming AC race is no different.

We have yet to see any of the other AC boats undergoing testing, so there will likely be many more opportunities to dissect and/or evaluate this latest AC design.

Finally, as you say, the AC teams are quite aware that many eyes will be on their progress and they may well be fudging their performance to throw off the competition.

Modeling boat performance on a computer program does not give the same real time evaluation as on-the-water testing so I'm sure many things will come to light soon enough.

I'm well aware that the whole purpose of the foil is to lift the boat out of the water to reduce drag, hence the phenomenal speeds, but given enough wind power and speed, the drag from another foil can be easily overcome . One must also assume that if two foils were to be used, their overall immersed footprint could be halved.

The foils appear to be minimally ballasted at best, so righting moment is really dependent on the on the weight of the hull trying to rotate around the leeward foil.

It may be that my opinion is entirely in error, which is ok by me, but the purpose of that missive was to provide an alternate point of view.

[jmh2002]

I applaud your keen interest in sailboat design, as I also have, in addition to being both an amateur and later a pro racing sailor in the past too, both sailing as well as managing campaigns.

If you have read every post here then would you not have already seen the answers to many of the missives that you propose in your posts?

This gives rise to my confusion because unfortunately some of the things you mention are just, well... (sorry to be indelicate) - somewhat incorrect.

Originally Posted by MicHughV

The foils appear to be minimally ballasted at best, so righting moment is really dependent on the on the weight of the hull trying to rotate around the leeward foil.

Again, respectfully, I think you are somewhat incorrect here (and Grant Simmer does too...).

The general principle is correct, but given that the foils are expected to weigh 1.2-1.5 tons, and with an effective beam of around 15m between the windward foil (raised) and the leeward foil (immersed).

The whole boat is only weighing 6-7 tons, so the windward foil could be up to 25% of the weight of the total package PLUS the lever arm of it being so far to windward.

I think that is more than just 'minimal' ballast effect.

And especially now that the boats will fly, the designs will try to make the hull itself lighter than ever before. I wouldn't be surprised to see a structural failure given the dynamics of the loads involved.

With your 'two foils always immersed' proposal you would both lose the additional righting moment PLUS add more drag. I don't think that is fast, but ok.

Here is a post from page 2 with some of these details.
You will note that the IMOCA boats in the videos do NOT have ballasted foils, and instead still have their canting keels to provide additional righting moment.

http://www.cruisersforum.com/forums/...ml#post2975040

Originally Posted by jmh2002

Here is some basic info for those not familiar with the concept.

Approximate dimensions:
Length: 75ft / 22.8m
Beam: 17.7ft / 5.4m
Beam incl Foils 49ft / 15m
Draft, Foils down: 16.5ft / 5m
Foil Weight: 1.2-1.5 tons each


How the new AC75 will fly:

The AC75 is the next step on from the IMOCA60 which introduced foils but still had a canting keel:

[jmh2002]

Here is a better video fly by from another day in more breeze with stable flight and the hammer down, some suggestions of around 40kn boat speed:

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

and Foiling with the Code Zero in 7kn TWS at around 24kn boat speed:

https://www.youtube.com/watch?v=6q8ZZOuHPVM

[Pelagic]

Originally Posted by jmh2002

........And especially now that the boats will fly, the designs will try to make the hull itself lighter than ever before. I wouldn't be surprised to see a structural failure given the dynamics of the loads involved.

This aspect actually has me quite concerned, as a structural failure could be catastrophic, leading to serious injury or death.

[jmh2002]

Regrettably yes, but I guess that is always a possible outcome in any high speed sport.

But that is not to say that older race boats were especially safer either just because they were going slower.

The maxis of the past, with massive loads, wire sheets and guys, etc, etc?
Not to mention a modern sailing superyacht, simply because everything is so big.

And isn't there a photo around of Dennis Connor wearing a crash helmet at the helm on a 12m to prevent being wacked in the head by the huge metal flying runner block?

As a bowman in the past getting hurt was often part of every day out racing if it was windy, and I've been off the boat a few times too, even once upside down and being towed through the water with a wet heavy bagged spinnaker on top of me. And there was no high tech gear and 'spare air' type safety devices back then either.

Sadly a fellow bowman that I knew was drowned at the end of a spinnaker pole by a crew error in an offshore race. Having been in the same spot many times peeling spinnakers it did make me think...

I think in general these guys at the top level are safer than ever these days.

[MicHughV]

Besides being a lifelong sailor, I am a structural marine engineer by profession (now retired) and I have to agree that one structural error or mishap here could have catastrophic consequences.

I note that these AC 75 boats sail pretty much with the mast in the vertical position with little noticeable heel, lending credence to my earlier thought of why not two immersed (but smaller) foils. Keeping these boats in an upright position must require enormous loads on the rig, mast, foils, etc

Much like sailing a trimaran, except the ama's would be foils..

Regardless, I'm sure some of the best engineering minds available have taken a looksee at this development. The foil is but one component. The attachment to the hull and the mechanisms to deploy it must also be taken into account. Finally, there is the means to provide the fluid pressure to activate the ram.
There are many pieces to this puzzle.

Without question, a foiling 75' AC boat moving at 50 knots is going to generate some stupendous loads all over the place. The respective crew of these boats would need to be at the top of their game here.
While a part of me would relish an opportunity to sail one of these boats, the safest way to enjoy this sporting event is to be a spectator.

This AC race is going to be a doozy no doubt. Sad that that there aren't more competitors.

[jmh2002]

First (very brief) sailing footage of INEOS Team GB (sailing just after the 1min mark):

https://www.sail-world.com/news/223198/?source=rss

https://www.youtube.com/watch?v=pR5pf42nIvE

[MicHughV]

I would like to make this analogy.

One may have seen these 3 wheeled motorcycles, two wheels up front spread apart 4-5' or thereabouts, with a regular wheel out at back.
A skilled rider with a good sense of balance could likely tip this bike up to enable him/her to ride on only two wheels with one front wheel up in the air. The rider would have to turn the steering slightly to make up for the "up" angle so as to proceed in a straight line.

The AC 75 boats, in my view, are much the same. That immersed foil is some 25' off-center from the centerline of the hull. Consider this 25' as the " lever arm". Basic math and knowledge of sail effort tells us that the total centre of sail effort would not be over the foil. Additionally, the rudder would have to be cocked to one side or the other to keep the boat going in a straight line.

The enormous spray seen emanating from the foil and rudder certainly appears to validate the fact that these foils are not running in line with the centerline of the boat and I would venture to suggest that there is considerable torque enacted on the submerged foil (and rudder) to keep these boats going in a straight line.

In summary, the foil (and rudder) must act in three ways. (a) to raise the hull (b) to resist leeward pressure and (c) resist torque.

At this point in time, for the most part, we have only seen these boats accelerate in a straight line. Pre-start maneuvers are going to be quite the dance, as well as tacking duels or even just two boats sailing in very close proximity to each other.

No doubt there will be a very steep learning curve involved here, especially trying to do all of the above at considerable speed.

I would be surprised if some or other structural failure is not eventually brought to bear.

I continue to watch the progress of these AC 75's with interest.

[Pelagic]

Another analogy is that they remind me of the 3 bladed ice boats I got to sail in Holland (Aalsmeer Lake)

Ironically, the Swiss may now have a historical advantage in reclaiming the cup [emoji4]
https://youtu.be/qC0I5PEhkJo

[jmh2002]

Originally Posted by MicHughV

The enormous spray seen emanating from the foil and rudder certainly appears to validate the fact that these foils are not running in line with the centerline of the boat and I would venture to suggest that there is considerable torque enacted on the submerged foil (and rudder) to keep these boats going in a straight line.

The foils may or may not be in line with the centre line, but I don't think that the spray validates anything especially.

Anything cutting through the water at high speed is going to create some spray and some wake, even a relatively thin foil.

You see spray generated even on powered foiling vessels, which are not sailing, and therefore don't have leeway to resist.

For interest, here is a screenshot from the new video I'm about to post, showing the wake viewed from astern.

I think it's relatively minimal for a vessel travelling at speed. I think the dramatic looking spray at other angles is mostly a red herring.

Review the TNZ high speed fly by video a few posts above (http://www.cruisersforum.com/forums/...ml#post2997118) for a better real world view on this. The spray is very thin and vaporised, a fine mist really rather than 'spray', and there isn't really any 'wave making' action occurring.

NB: for comparison, also remember that TNZ's foil fairings and wings are smaller than the other teams (so far).

[jmh2002]

Still not the best footage but here is a new video. This is still highly curated official footage from Team GB so let's wait for the third party images and videos to see more.

https://www.youtube.com/watch?v=O0W2_aUeqXo

[MicHughV]

We can go round and round on this issue forever.

My contention is that these foils and rudder throw off considerable spray, denoting that they are not aligned with the forward motion of the boat.

My issue is not so much sailing performance, but structural ability.

These foil stems are apparently all the same for all the boats, coming from the same supplier, with each team being allowed to modify only the foils and the fairing.

Lastly, I'm pretty sure the designers of these foils must be aware of this and am wondering, if these foils like, like a keel or wing, are intended to be this way so as to have a low pressure and high pressure component.

I am intrigued by this concept and must deduce my own thoughts on the matter from only the video's I've seen and would love nothing more than to have an in-depth conversation with the designers of these boats to fully understand the different approaches taken by the different teams as to why a particular foil shape, angle, winglets, etc is chosen.