New Catamaran Foilers

"Easy to Fly" does not use wands?

 

This video was taken with a Kodak SP 360 put directly on the leeward ama side to the foil root :
Kodak Digital Cameras | SP360 Action Camera https://kodakpixpro.com/Europe/fr/cameras/actioncam/sp360.php
Earplugs ? : no (for such cata) , yes (for foil assist Imoca)
No : for such foiler if I refer to testers comments, although they mention the more or less high frequency of the whistle because it is the only remaining noise you heard when you take off and fly, as the hulls are no longer in contact with water (source : Voile magazine Jan. 2017).
Yes : for skippers of Imoca 60 when at more than 20 Knots with foils : it is a hell of noise inside these light carbon structures, with both water impact and foils whistle, they all complained about that, to sleep in these conditions is challenging.
Foil assist Ultims are a lot more comfortable from that point of view too.

 

They pass one monohull (about 1:12)and one catamaran (about 1:39), both just two–sail reaching. You'd expect an 8m high performance cat to go screaming past, foiling or not. ;-)

 

As I understand, the whistle appears for speed higher a certain value, let'say about 20 knots

Not seen, neither mentioned by testers. For altitude control, it is supposed to rely on the S + V shape of the foil, S to change the "quant" and V to regulate the altitude. Upwind, the foil is fully deployed to have both more lift and more lateral resistance. Downwind, the foil is partially deployed. To retract the foil, just to open a blocker. To lower a foil, one uses a hoist. (Source : Voile magazine - Jan 2017).

 

In complement, here attached photos of this S+V shape foil.
On their Facebook EasyTF , a lot of short videos are available + some comments of the first owners (one UK and 3 Swiss) :
Easy To Fly https://www.facebook.com/EasyTF/videos/

 

Dolfiman, it seems to me like too many of the designers that are using the "up-tip" (UptiP) foil discovered by TNZ fail to give credit for the principle behind the foil (leeway coupling for automatic altitude control) by at least using the name the original designers gave the foil(see below)-what do you think?

Link to Part 1 and Part 2: America's Cup 2007 2010 2013 - Feature Articles Index - From Cupinfo.com http://www.cupinfo.com/en/featuresindex.php
Quote from the article,Part 1:
When we were working on the rule, we knew you wanted to get as much lift as possible when you were going fast downwind,” Melvin says. "For instance, in the 2010 America’s Cup, sailed on giant multihulls, the maximum amount of lift we thought we could get was about 50% of the weight of the boat. At that time, we were still relying on the hull to provide pitch control, so what’s come out of this is the boats all now have elevators (the horizontal foils on the rudders).

“At Team New Zealand, we developed a new type of foil that allows you to keep your height above the water more or less steady. No one had been able to do that before, at least not on a course-racing boat that was not going downwind. We developed that mostly on our SL33 test boats -- they came with the stock constant curvature “C” foils and with those kinds of foils, you can generate 50% boat weight lift before they get unstable. But we noticed that when we could get one boat up fully foiling for a few seconds it would really accelerate away from the other boat – and that got the wheels turning. How, with such a huge potential benefit, can we achieve stable flight downwind? So our design team came up with the “up-tip” type of boards. We refined those on the 33s and our 72 is designed to do that and fortunately it worked right of the box.”

 

Believe that the speed of whistle onset depends on foil geometry and dimensions as well as the internal structure and immersion depth. We can expect foils to become thinner (higher loading) and more solid (less internal damping) so the whistle can be expected to occur at lower speeds?
Many thanks for the PDF of the S-foils. The taper toward the tip is striking.

 

Humming foils are usually from oscillating vortexes from the trailing edge of vertical struts. Look for "Karmen vortex oscillation" on YouTube, search in Google for "humming rudder", though centreboards also hum.

A simple fix is to chamfer the trailing edge at about 45° to bias the flow and stop oscillation. It may have a slight effect on speed. I used to have a rudder that started humming at around 15 kn, by around 22 kn it was really noisy. Mild treatment with wet 'n dry made it much quieter, but I didn't mind a bit of hum as it was like an audible speedometer.

On the Artemis AC50 the screaming from the rigging was so bad they had to fit attenuators so broadcasts from the boat didn't have the audio overwhelmed by their noise.

 

If you turned the rudder even slightly at 22 knots did the humming stop?
Vortex shedding is extremely well-known as are the solutions. Maybe there is another cause. Interesting.

 

Not that I remember, but at those speeds you don't turn it very much. I think it stopped when gybing, though I don't recall the speed as I wasn't looking at it but likely down around 15 kn as I didn't have the courage to gybe at high speed. I was more worried about ventilation, which is a real pain.

It would be nice to go out and try some experiments, but while I still have the rudder, I don't have a foiling boat to put it on anymore.

 

That makes sense. turning the rudder creates asymmetric flow across the rudder.
From memory vortex shedding is most prominent on symmetrical foils with symmetrical flow. The chamfer solution creates an asymmetrical profile in a highly local area, trailing edge only.
Flutter is a well understood problem in high speed planes, the wing twists as lift is generated until the twist stalls the wing, usually at the tip. The stiffness of the wing snaps the tip back down and the cycle is repeated.

 

from catsailingnews.com -foiling gybes with an S9:

 

Why do you Think this looks so much more stable than the superfoiler? They seem to have more or less the same size, but the superfoiler has a lot of buttons to control the foils, while this doesn't seem to need them.

 

Listening carefully there seems to be 2 main whistle components (main foil and rudder foil?) plus a lower frequency hum (hull response to foil vibration?).

 

Speed Foiler, first mentioned on p5 of this thread is again mentioned in www.catsailingnews.com today. About the same size as the SuperFoiler trimaran.