Jump to content

ETNZ sucks big hole


Guest

Recommended Posts

So did you have any idea what you'd find under a thread title like that? I'm guessing knot ;)

 

 

 

Anyway, 2 photos. One is the original and one is a blown up crop.

 

Look at that hole and consider the loads on the board. How high must the pressure be on the bottom side if the low on the top is doing that?

 

Also if you want to know something about ENTZ that Russel Coutts swore he had no idea what was there just a few days ago, take a look at the wing on the rudder and you will :lol: :lol:

post-646-141887222581.jpeg

post-646-141887222584.jpeg

Link to post
Share on other sites

Wow that is like a waterfall.

 

Even the pressure wave around the board is impressive.

 

It looks like the wing/fin is sucking the ocean Down the " plug hole"

 

I guess the V configuration just draws the water down by venturing effect?

Link to post
Share on other sites

I don't find this really unexpected. The foil creates lift from underneath by reducing pressure on its upper edge. As it travels through the water, it leaves this low pressure behind. The surface of the sea is sucked down to fill the void. Very noticeable on this foil config. It's really very clever - a foil that provides lift, resistance to leeway, and is self adjusting for ride height, all at once. Great PIC of great engineering!

Link to post
Share on other sites

This is not new. The foiling ferries had then years ago.

 

They still run these V formation foils on Ferries out of Piraeus in Greece.

 

I think the Auckland ones were similar. The foil acts like a planing hull and displaces water as Island Times has suggested.

Link to post
Share on other sites

Actually topsail, these foils are new. They are not simple v foils. And the ferries are not primarily supported often on one foil. The curved shape gives some lift, but most is leeway resistance, as it becomes increasingly horizontal, it provides more lift, less leeway resistance. After the tip 'corner' it provides lift at some points of lowering, and, when fully lowered, ride height control. The ferry ones don't do that. They are complex in design, more so than any we have seen before. Ferry foils don't lift at all, and have fixed geometry.

This is the innovation for ETNZ this time. The AC class rules were written expecting no boat to foil. Perhaps foil assisted, but not full foil. That's why the other teams are playing catch up.....

also, note the foil for and aft positions - oracle's foils are further fwd, relying much more on rudder foils for fore/aft stability - hence the ruddergate issues...

Link to post
Share on other sites

That is a really old photo with TNZ's first generation rudders it was the subject of much debate on SA and after seeing them ripping up the course in sanfran I think it's safe to say that it isn't detrimental to their performance.

Link to post
Share on other sites
Actually topsail, these foils are new. They are not simple v foils. And the ferries are not primarily supported often on one foil. The curved shape gives some lift, but most is leeway resistance, as it becomes increasingly horizontal, it provides more lift, less leeway resistance. After the tip 'corner' it provides lift at some points of lowering, and, when fully lowered, ride height control. The ferry ones don't do that. They are complex in design, more so than any we have seen before. Ferry foils don't lift at all, and have fixed geometry.

This is the innovation for ETNZ this time. The AC class rules were written expecting no boat to foil. Perhaps foil assisted, but not full foil. That's why the other teams are playing catch up.....

also, note the foil for and aft positions - oracle's foils are further fwd, relying much more on rudder foils for fore/aft stability - hence the ruddergate issues...

 

I think you will find that the V foils on the Pireaus ferry are very similar in configuration and shape albeit they have to have four of them as they are lifting huge weights ( as these are big passenger ferries).

 

The chord shapes are different as they lift of at at lower speeds.

 

Remember these ferries were designed and built in the 50's.

 

The difference is carbon fibre construction technology and weight.

 

Very similar I think.

Link to post
Share on other sites

Sorry TS, I don't agree. But hey, we can agree to disagree! :D

 

It seems the subtleties of foil design escape you. The Ferry ones are conventional foils designed only for lift. And a set cruising speed, so they don't ever try to become airborne. Chord on a straight edge is very simple mathematically compared to a curved foil..

 

A yacht is much more difficult, as is effectively a single lift point. Large increases in power (gusts) must be controlled without becoming airborne (too much lift), as well as dynamic directional stability. The Ferries have none of these complications, and these AC boats are once again leading a new technology development. :clap:

 

ALL FOILS will create that hole - basic physics - for every action there is an equal and opposite reation - it's just in that case of that ETNZ photo it is well displayed. A very deeply immersed foil may not show much at the surface...

Link to post
Share on other sites

What about how much load goes on it when they drop the board at 35+kts heading into a gybe. ?? 35kts is around about the sht ya pants speed for waterskiing, because the water goes from hard to extra hard.

 

So how do they get the board to submerge without ripping the hull in half??

Link to post
Share on other sites

Unlike a flat board on top of the water (ski) the foil is a wing and fly's through the water. To work properly, it must have water above it. The hole in the Pic is because the water is being forced down due to the foil wanting to lift up. Hence how so much power is developed using such a small area. A flat surface like a Ski simply could not do it till much higher speeds are reached and then you start getting all sorts of other "distortions" occuring.

Link to post
Share on other sites

Some will be leeway, but I's suspect in that pic the foil is not far below the surface, and most of it is,as Wheels said, the reaction of the surface to 7 tons of lift - probably more - it is not just the mass of the vessel it is holding up, but also the load on the wing, on lever!! (Beam). That downward pressure is making a "hole" or dent in the surface. It sure would be interesting to look at the loading calcs!! Sure that is not going to happen....

Link to post
Share on other sites
I can't imagine "sucking" the water down is the cause of this.

Nonetheless, it is.

 

Disregard the high pressure / low pressure stuff; it is correct but doesn't _quite_ get to the heart of the matter.

The force referred to as lift is essentially created by deflecting the fluid medium in the opposite direction.

You can either deflect a LOT of fluid a LITTLE bit (as in a slow aircraft with a large wing) or a LITTLE bit of fluid a LOT (as in high-speed aircraft).

In this instance we've got a tiny "wing" deflecting a LOT of fluid to generate the necessary force.

Link to post
Share on other sites

I think my understanding of water dynamics is gained from the bath so perhaps I need to get out more.

 

From that photo the wing isn't just under the surface.

 

If I was trying to create the same effect, I would take a paddle and pull it through the water quickly. The blade pushes the water out of the way, creating a hole behind itself.

 

Leeward drift is my vote which might be why they are not trying the foil upwind.

Link to post
Share on other sites

Don't agree, sorry. About 98% of it is caused by the lift. A guesstimate of depth below - maybe 1m or a bit more. Look at pic 1 - you can see board length on port (windward) board, and you can see the top of the stb board...

 

If it was all leeway, the boat would be making a hell of a lot of leeway (45 deg??)...

Link to post
Share on other sites
About 98% of it is caused by the lift.

That is correct.

What is taking place is quite dynamic and unbelievably complex. Hence actually why true foil technology is such a new science. Those old foils of yesteryear on the old Ferries were in fact more like a Ski than a foil.

In fact how a Wing actually works has only been rather recent knowledge. The theory of low pressure above and high pressure under a wing (bernoulli's principle) is not entirely correct and also not the entire story of what is taking place. A slight aside..... if you work out square area of a wing, or sail in our case and then multiply that area with the force Bernoulli's equation should give us, we get on paper, a rather dismal lift sum. A Sum that is actually no where near what is actually being generated in reality. There is much more taking place. I can't do the story justice, but I will try and explain simply.

So firstly, the main Bernouli principle has now been replaced by this.

http://www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html

The next part I will tackle is the last part in the story. "Every action has an equal and opposite reaction". As the water (or air) leaves the wing, it's direction has been changed. This change in direction means a Mass is now applying a force.

The third influence is something quite unique. It is a force that is generated out in front of the wing. Air or water that is traveling toward the wing is bent and flows into the Wing well forward of the leading edge. This creates a tremendous force that is likened to extending the size of the Wing/Sail or whatever it is. This is where the extra "missing" force is to be found. If you take a look at the animation, you will see a little of what I am talking about, with the flow being bent well out in front of Foil.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...