Jump to content


A-Cat Wing


  • Please log in to reply
109 replies to this topic

#101 SimonN

SimonN

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 8,960 posts
  • Location:Sydney ex London

Posted 08 September 2012 - 12:14 PM

I do believe that pitching really is a major issue, and that it becomes more so with lifting foils rather than less. I base this on a number of facts. First, I have a very different view to you about pitching in an A, even with a carbon mast. The fisrt time I sailed in waves (Botany Bay), I was truly horified by the pitching compared with almost any boat I have sailed before. I have discussed this with a number of top sailors in the class and this is why they use PBO (or carbon) rigging at venues where there is chop, fit carbon battens and why recently, one of the guys has made a mould to manufacture carbon spreaders.

The second thing that convinces me is that the one person with lots of experience of a wing on an A is Ben Hall and he reported that the inertia problem was a huge issue. He called it "the tail wagging the dog" and at the worlds that were held in Florida, it killed him. He was seriously quick downhill but reached the windward mark a long way further back than he would have done witha conventional rig.

Finally, I but 2.5kgs of lead on my mast at the spreaders to see if it made a difference and besides being scared it was going to break the mast, the increased pitching was serious. I hate to think what it would be like with 5 kgs and a bit higher.

As for the lifting foils, I believe that the problems are much worse. Pitching, as opposed to riding up, over and then down a wave has a very significant effect on the angle of attack of the curved boards, the bow is forced up and the AoA increases, probably past the stall point for the section. As this is working through, the bow begins to dip due to loss of lift just as the boat pitches bow down so thge pitching is worse. As flow re-attaches, the boat is bow down so the foil is no longer lifting but might even be pushing the bow down. Simply put, I believe that we see increased and uncontrollable hobbyhorsing, which you have to control by backing off and moving the body to an extreme, losing many boatlengths at the same time.

I don't believe that the foils provide enough lift to overcome the extra moment of inertia. The problem is length. On a C or bigger, the extra lengthchanges the whole pitching dynamic. In addition, the A's rig is so refined that the gains aren't enough to overcome the shortfalls. I also find it interesting that Ben Hall has speculated that it might well be worth building a C with an A Class style mast and soft sail, making a far lighter boat and that the weight reduction would more than compensate for the reduced rig efficiency. I am not sure i agree with that, but it shows how much the whole pitching thing got to him!

#102 mitchellsailor

mitchellsailor

    Member

  • Members
  • PipPipPipPipPip
  • 42 posts
  • Location:GLYC
  • Interests:SAILING, yacht design, hockey, girls

Posted 08 September 2012 - 02:45 PM

-brain farting- but as you say Simon someone might enjoy these seeds
A soft sail on a C would not make it a lighter boat? they are able to be made very light bcause there is very little rig tension/ mainsheet tenson requirements. but obviously the point of inertia would be lower which is the main point..
an A class platform has never been made specifically for a wing!! (missing half the equation so far maybe?) and it obviously can't be made any lighter because of the rules to exploit the smaller needs for strength. disregarding the rules how much lighter could an A platform be made in current configuration? and how much lighter again could it be made if a specific wing platform?
disregarding all the obvious Inertia problems how fast could an A class with wing and say 15kgs lighter platform be!!

#103 hump101

hump101

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 280 posts
  • Location:Brittany, France
  • Interests:Naval Architecture structural engineering, speedsailing, offshore racing

Posted 08 September 2012 - 02:47 PM

Ben Halls experience is absolutely pertinent and it would be interesting to get his input, as the devil really is in the detail for this phenomenon and, for example, the hull shape of the boat he put the wing on, and whether he had leading edge twist, would significantly affect his speed to the top mark. Your experience in Botany Bay was with a narrow transomed boat (i.e. before you did the mods)?

Regarding your description of foil behaviour, I'm not clear on your order of events. As pitch is instigated, the bow rises as it enters a wave, which reduces, or even negates the angle of attack of the foil due to the momentary local heave velocity vector combining with the vector of forward motion, not increases it as you state? Or are you referring to foil-induced pitch, in which case we are not talking about the same thing?

In normal circumstances the change in foil AoA due to wave-induced pitch rotation is to generate a foil force that acts in the opposite direction to the local heave velocity, provided the section does not stall. Bear in mind that the local pitch-induced heave velocity is 90 degrees out of phase with the pitch rotational displacement, so provided the LCF position is aft of the foil location (which it needs to be for a foiling boat, hence my question above) then the foil will tend to damp pitch motion, not increase it. If the LCF is forward of the foil the opposite would occur, with unpleasant results.

That's the theory, anyway, though I've no experience of a foil-assisted beach cat so I bow to your greater experience. Nevertheless, from a theoretical standpoint, if you mount a wing on a hullform that is specifically designed around its dynamic characteristics then you should be able to design out the pitch issue, that is reduce pitching to similar levels seen with the lighter soft rigs, and there will be encounter frequencies that will give improved motion.

The question then remains as to whether that hullform would be as competitive as the current best shapes. My best guess is that it would in enough wind or no wind, but there would be a transition windspeed when you would have to choose stable or fast, and that could get expensive with a wing!

#104 juniordave nz

juniordave nz

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 301 posts
  • Location:Christchurch

Posted 09 September 2012 - 10:17 AM

http://picasaweb.goo...imyLxWV3cHTLPA#
Are these photos of Bens Rig?
I believe it could take that long and that much is you wanted to spend that type of money. But I recon you could do it a lot cheaper too.
With regards to the weight issue I kind of agree with hump. I've got an alloy rig and it plus the sail probably weight the same as a wing. I can imagine that putting a wing on a standard hull might not work. But designing a hull that is made to have that extra weight up high could work. But then again, is it all worth it, weight up high still isn't good, even if you don't pitch all the time and is a winged A-class going to be quicker round the track than a soft sailed one? I guess that's still to be answered.
Wings are awesome though

#105 Catnewbie

Catnewbie

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 318 posts
  • Interests:High Tech Catamarans

Posted 09 September 2012 - 11:56 AM

Hi Everybody,

Unfortunatly you are right about pitching Simon, pitching is likely to kill the wing power at the top.

Only, reasonning by analogy, I can find one argument which supports the wing solution:

If you consider a 75kg A Cat with a 25 kg wing and a 85 kg crew,
you have similar ratio than a 170 kg C-Cat with a 55kg wing and a 170 kg crew,

If similar ration, and if similar disadvantage for the heavy wing, why dont we see C-Cat with a soft rig ?

Intuitively I thought that both A Cat and C Cat sail in similar conditions with similar chop and waves, consequently if C-Cat are much less affected by the chop and waves, the explanation could be the longer C-Cat hulls/relative to chop and waves, otherwise we sould see soft rig C-Cat ?

I think Hump provides a much more academic analysis to this problem. But I need to do some homework to understand that in depth.

A question to you Hump: you are in Briittanny, so did you see a wing build for a F18 by Desjoyeaux or another big boat top sailors,
I have been told the F18 wing is in Port-Laforet ?

There is also another point with a soft rig, the compression loads might increase more than proportionaly to the size, and a C-Cat soft rig would not provide the same weight advantage, than for an A-Cat ?

Pushing the idea further: It seems that Alinghi's soft rig did not had any significant weight advantage over BMW Oracle's wing ?

May be there is a breakeven point beyond which, the wing is superior, and conversly ?

To be sure we have to wait to see how Tillo wing's will perform in chop!

Cheers all

Wolfgang

#106 hump101

hump101

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 280 posts
  • Location:Brittany, France
  • Interests:Naval Architecture structural engineering, speedsailing, offshore racing

Posted 09 September 2012 - 04:46 PM

A question to you Hump: you are in Briittanny, so did you see a wing build for a F18 by Desjoyeaux or another big boat top sailors,
I have been told the F18 wing is in Port-Laforet ?

Sorry Wolfgang, I haven't. We are the other side of Brittany.

#107 captain horizon

captain horizon

    Newbie

  • Members
  • Pip
  • 24 posts

Posted 09 September 2012 - 10:30 PM

http://picasaweb.goo...imyLxWV3cHTLPA#
Are these photos of Bens Rig?
I believe it could take that long and that much is you wanted to spend that type of money. But I recon you could do it a lot cheaper too.
With regards to the weight issue I kind of agree with hump. I've got an alloy rig and it plus the sail probably weight the same as a wing. I can imagine that putting a wing on a standard hull might not work. But designing a hull that is made to have that extra weight up high could work. But then again, is it all worth it, weight up high still isn't good, even if you don't pitch all the time and is a winged A-class going to be quicker round the track than a soft sailed one? I guess that's still to be answered.
Wings are awesome though

Yes that is my wing. Not sure where Thilo came up with so many hours and some many $$$ to make his wing ?
I had about a total of 400 hrs and about $2500 in materials. I hope we see his wing at the Worlds but judging from his recent soft r,ig victories using a new Landy sail, I doubt it. Did he ever try it in a race. From all the published info, his wing sounded about 3-5 kegs heavier than mine...a pitching nightmare, especially in Islamorada.
And yes I did consider building a C with a soft rig....briefly...until relatity checked in. A lot of money for an outside chance of competing against the good wings. At that point there was a lot of room in the hull design area. I figured that we could build a boat that was 50-60 lbs lighter than the lightest wing C out there. Just might make sense but.....
I used the very good EVO design for my wing A Cat. I made the beams lighter and was able to make minimum weight. The hulls were quite full and were a good match for the wing. The rig definitely performed well in smooth water and most any condition downwind but on the average was not as good all around as the well developed soft rig. Simon makes some interesting points about curved foils but maybe with addition of rudder T foils the wing package could work.
And yes both elements of my wing had twist controls.
If I had to do it all over again I would change a bunch of things. I would not bother with having it break down to fit in a short trailer. Make each element full length a get a bigger trailer. Simplify all the controls to save weight. Use lighter materials that were not available in 2007. Bottom line the wing should weigh in at 20 kgs to be competitive.
See you in Islamorada.
Ben
USA 99

#108 Scarecrow

Scarecrow

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 3,623 posts
  • Location:Melbourne, Aus

Posted 09 September 2012 - 10:41 PM

I was laying in bed pondering this issue at 2am this morning (having by that stage drafted this weeks boat maintenance to do list, and theorised how I would go about working out how much lift to design into AC72 foils if any of the AC teams happened to ring me up and ask, you never know) and the only way I can see A's getting past the pitch issue is L or T rudders. My logic is as follows.....

There have been a couple of comments in this thread (possibly one even from me) saying that to make the wing work you need to design the hull to minimise the pitching, but how is this achieved? To dampen the effect of pitching once it starts you need to increase the prismatic coefficient (move volume to the ends) this means that when the rig tries to drive the bow or stern down the hull will resist this force. The problem with doing this is a boat with higher prismatic will be effected more by the waves which in turn will course the boat to hobby horse and pitch more, so you end up trading the amplitude of the pitching motion against the speed with which it will be dampened out. Go the other direction and take volume out of the ends and you'll get less excitation of pitching as you pass through waves but the hulls will have no inbuilt dampening and the boat will continue to hobby horse for a lot longer. The third option is to add a bucket load of rocker, this will provide a level of dampening once pitching starts, the problem is it probably won't be able to get out of its own way at speed.

Where would I go from here:
Design the lightest possible wing with lowest centre of gravity possible.
Take even more weight than normal out of the ends of the boat, weight in the front and back of the boat will have exactly the same effect on pitching as weight up high in your rig.
Give the boat the pointiest possible bow, it needs to be the most "wave piercing" bow you have even seen.
Possibly consider flaring the transom to get some damping from that end if she starts to pitch.
Fit L or T rudders to dampen pitching once it starts.

#109 lesburn1

lesburn1

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 360 posts
  • Location:40:09:01.3 -75:07:29.5
  • Interests:A-Cats and 18Sq meters and now AC more then before...

Posted 09 September 2012 - 11:33 PM

http://picasaweb.goo...imyLxWV3cHTLPA#
Are these photos of Bens Rig?
I believe it could take that long and that much is you wanted to spend that type of money. But I recon you could do it a lot cheaper too.
With regards to the weight issue I kind of agree with hump. I've got an alloy rig and it plus the sail probably weight the same as a wing. I can imagine that putting a wing on a standard hull might not work. But designing a hull that is made to have that extra weight up high could work. But then again, is it all worth it, weight up high still isn't good, even if you don't pitch all the time and is a winged A-class going to be quicker round the track than a soft sailed one? I guess that's still to be answered.
Wings are awesome though


Yes these photos are of Ben's wing. I took the at the Lake Hopatcong YC in 2007.

Some more shots are at http://mysite.verizo...ats/images.html


#110 Waynemarlow

Waynemarlow

    Anarchist

  • Members
  • PipPipPipPipPipPipPip
  • 223 posts
  • Location:As far from the sea as possible in the UK

Posted 10 September 2012 - 03:13 PM

Fit L or T rudders to dampen pitching once it starts.

The Stealth F16's ( designed in 2000 ) have had T Foils for a very long time, their premise was to stop the shortish 16ft hulls from hobby horsing and stabilising the hulls and sail plan. In practice they succeeded far more than one would think, perhaps not in the way we thought but through a combination of stabilising the hull by dragging the back down once the nose had started to become a little submerged and perhaps as much by giving the skipper a bit ( actually a lot ) of pre warning of what the boat was doing by giving feedback with the noise and feel of the boat when the T foils AOA has started to get to the stage of really working the foil shape.

Later Stealths had a quite small T foil to counter the doubters who alway quoted that the drag they caused was not worth the gain. Personally I have felt the only excess drag was the weed and bits they always seem to attract. As I have got better and understand the boat better I eventually changed to normal rudders as I found they I was burying the nose less and less and breaking the foils more and more through launching accidents.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users