There is an interesting discussion on the A class site on the current rule on the use of foils. http://p078.ezboard.com/faclasscatamaranforumfrm2.showMessage?topicID=67.topic

It seems some in the class are feeling threatened by the moth class and are thinking they need to allow foils to maintain their cutting edge image. Tough issue for the class, on one hand the cutting edge status attracts people to the class, on the other hand this decision could render a lot of hardware obsolete.

I wonder if an existing platform retrofitted with foils would be as fast as an A cat designed from the outset to be a foiler? I doubt it.

It depends on the type of foil and extent of the retrofit.

Thanks for the link, the discussion is interesting. Apparently they need to know more about foils, even if only to discuss their current rule.

I think it is not only good, but necessary, to have at least one multihull development class testing foils.

Luiz

Dave C fitted foils on his A Class cat several years ago and think is the reason for the A Class rule which also states in part that no board may extend beyond the 7,5 beam limitation in a lowered or raised position ,--which in effect means not only no hydrofoils ,but no angled boards which have been proven to be very effective and should be developed further .

Maybe we need the resurgence of the 18 sq class ,-though would like to see an open development 20 class emerge and race events for them to test within .

It seems difficult enough just to get a group of production cats together these days ,-hope that changes again soon, but will only change as new innovative fun high speed sailing craft are developed and made available ,-much as Hobie Alter accomplished in the 70s early 80s time frame - we are overdue for another innovator and innovative design to get new interest.

thanks for the info and link .

This looks a pretty good way to Fly.
see attachment
and http://gallery.sailmelbourne.com.au/smgallery/album66?page=2

What the heck is that? I want one.....

Its an International Moth fitted with uni-foils.

www.moth.asn.au is the class website. The foils are probably by www.fastacraft.com
You could also talk to www.windrushyachts.com as Brett was the first to use foils and win in an International Championship.

I want one too! Quickly reading the site, it seems that the hull would be easy and cheap to build. On video 1 below you can compare two moths, one with and the other without foils.
video 1
video 2

If those wings were shaped more like airplane wings, I wonder what would happen.

"If those wings were shaped more like airplane wings, I wonder what would happen. "

I dunno, but I`d swop the peak cap for a good crash-helmet !
I think you`d also need to apply for at least a hang-gliding license, too.
How the freak do those things stay balanced ? Imagine sailing it in gusty, switchy conditions.

Steve

Skipper skill

If you are young and skinny, hull width at waterline 15 cm
If you are old and fat, hull width at waterline 30 cm

Try to imagine building a winged monohull by using the rig, wings and one hull of a Hobie 17.

I like my catamaran.

In looking at all the Moth photos, it appears that some of them have wings that are just bare pipes, some have sort of solid trampolines, and some have open netting, and some a combination of the two. I am wondering what the advantages and disadvantages are of each. And whether those advantages/disadvantages are different depending on whether it is an on-water boat or hydrofoil boat.

I'm sure this information could also be applied somehow to multihulls.

The answer is moment enertia, same as keeping a cat on one hull.

By moving out the moment of enertia increasing slowing down the angular accellerations give a human mind enough time to react by steering and using the centrifugal forces of steering a curve to restore the balance. There is also a 3rd very important factor and that is the sing of the rig. It acts as a very large daping device. When the rig falls to luff the angle of attact is increased and so too the lift, result the angular accelleration is much reduced. All works the other way around when falling to lee. This factor also works when boat is moving very slowly.

I mean how do we human being rid a bicycle and even without any hands on the steering bar after we have gained experience enough ? Same principle. It gets harder with less speed as you can't make the S-curved to regulate the instable system as effectively as before.

This all is fun stuff, can you tell that this is my field. (control engineering)

p.s. in gusty conditions these guys use flexible masts that bend away in the gusts overwise the reaction time would be too small for a human being.

If you want some quick response on a sailcraft than try land- or ice yachting (with exception of the DN yacht with there VERY bending and yielding rig). These craft sail on two wheel or two scates nearly all the time with enough wind. And at those speeds the response can be quite rapid (not much enertia helping your there. You'll need a soft hand on the steering.

Wouter

Hey Wouter, interesting point if I understood you well (which I´m not completely sure...), I´m a collegue by the way. You are talking about moving the weith out (trapezing) causing similar effect as moving the weight to the inside of the curve on a bike?
I´m trying to follow you so I can improve my technique for sailing on one hull (I just have 2 weeks of experience there). I thought the effect of powering/depowering the sail when steering would be more significant than the change on centrifugal force? In other words, if I´m tending to capsize, I won´t turn downwind to get the hull down by the effect of reducing angular acceleration. I will rather turn upwind to depower the sail and stay away of the risk.. Up to that point the trapeze variable would be at 100% anyway, so it probably wouldn´t help either.
Perhaps you refer to a reduced range of operation, where manipulated variable won´t get saturated and provided that the sail angle will not vary up to the point of loosing wind. I will try it.
If I manage to go the the beach again, holidays are off for me...

Hi all
The spitfire cat project along with Moth hold some design promise for future development and applications -
more info search BDG Marine. Home of the Spitfire 12.

note to Andinista
Sailing a high speed cat the skipper can luff into the wind to prevent capsize only when close hauled or close reaching ,-most other conditions when sailing with the wind aft of 70 degrees the skipper needs to bear off to prevent capsize . With a spin rigged cat with spin up --always bear away in gusts to prevent capsize while keeping speed .
- hope that is helpfull from a practical perspective ,

all the best
Carl

I think you lost me here a little bit.

I can inteprete you quote in several ways but, since you're a collegue, I'll assume you are refering to fact that a cyclist must first countersteer shortly before he makes the curve he wants to make. He first has to cause a heel towards the inside to the desired curve before he can steer that curve. Otherwise he will only be thrown off to the outside of the curve he wants to make.

No, what I was trying to say is not really similar.

What I was trying to say was :

-1- Moving the weight further out from the fulcrum makes the whole system react more slowly. (a few if's and but's here but I will avoid these to keep it clear)


Think of it in this way the same gust will now only result in smaller accellerations as the moment of enertia has increased. This delays the system to within human capability.

-2- Humans can regulate quite a few systems well as long as they approximate a single integrating behaviour. The force - enertia system is one of such systems.

-3- By using the centrifugal forces the sailor can excert significant control forces on the system in a predictable and linear way. Much like a cyclist does in staying on the bicycle while riding and when making corners.

You will find now that skiff sailors are much more trained in this than catamaran sailors. A big difference is that when a skiff, 49-er for example, is overpowered by a gust then you can't head up to save you're skin. You will flip over immedaitely as the result of centrifugal forces. Catamarans CAN because their ratio between rig power and moment enertis is much larger this slowing down the whole system to such an extend that they can risk flying a little high and sheet sufficiently out in the mean time to bring balance to the system. Skiff sailors can not. Same with landyachting, you crash badly when you head-up as soon as the luff wheel lifts. What these guys do is bear away rapidly when overpowered using the centrifugal force to put the wheel/luff part of the craft down and thus buying themselfs time during which they can ALSO sheet out enough to balance the situation before steering upwind again to permanently stabilize the whole situation. And yes it goes wrong sometimes.

-4- By putting a higher rig on a craft you great a large damper component in the system. The top of the mast must really sweep through the air for each degree of rotation then. So by travelling out you can increase the height of the rig and thus AGAIN slow down the system when it responses to the gust hitting. Giving you time to sheet out sufficiently or depower in another way.

-5- The rigs can be made bendy so the impulse is shaved off to a broader and smaller in magnitude push.


All tricks to slow down the repsonse of the system to the gust hitting and give time for the human to compose and execute a control strategy.

One important thing as the human is only interest in maintain a certain attitude his is less hampered by the delay effects of enertia etc. And if he is than he has time to integrate back to the prefered attitude as long as he is never to far away from his reference position.


So, by adding wings and moveing out the moth guys do :

-1- Increase the overall rotational enertia of the whole setup. Slowing down the system. Notice how this also reduces the effects of gravity ?

-2- fit a taller rig, thus implement a large damper

-3- Speed up the boat so any given change of direction will cause larger centrifugal forces that can be used as control forces. This is actually a human controlled servo system

There are several other factors but the idea is to show that by reducing the speed of response of the craft to the onslaught the control comes more an more within the grasp of a human being. And secondly, moving out leads to large capsize moment indeed when the falls away completely but by increasing the moment of enertia and the decreasing the effect of gravity (again slowing down the system) the positive effects heavily outweigt the negative ones.

Actually imagine it like this. It is far more difficult to control the craft from near the centreline of the boat (with adjusted) rug than it when you are far away to the side of the centreline (with the normal sized rig).

This feels contradictionary but it isn't. An example. A low bike (lay down bike) is more difficult to control than a bike where you are sitting high and tall. Even when using the same sized wheels and the gyroscopic effects are the same in magnitude. That part of cycling looks the same as sailing these craft. OHH, imagine what you do when you get hit by a gust from the side. Do you head up immediately or do you rapidly bear off, bring the heeling back under control and only then head into the wind ?

That should answer your question.



>>I thought the effect of powering/depowering the sail when steering would be more significant than the change on centrifugal force?


dependents on the (design of) the boat. With skiffs you can't respond to a gust as a cat can. Some cats won't allow you to do so either. And some yachts can be pointing straight to the wind without complex strategies. MInd you all, 90 % of this is complete subconsious (reflex)


>>>In other words, if I´m tending to capsize, I won´t turn downwind to get the hull down by the effect of reducing angular acceleration. I will rather turn upwind to depower the sail and stay away of the risk.

You'll try that 1 time on a winged skiff or landyacht I can tell you that. This approach works on a cat however. I haven't experimented enough with the skiff approach on a cat to give more comments on the benefit of it when used on a cat.


>>Up to that point the trapeze variable would be at 100% anyway, so it probably wouldn´t help either.


?? you lost me here. Also it is not only about the crew but also about the weight in the rig and other factors.

Again on a car you have so much excess stability that you can just head up into the gust but on a motorcycle you first need to get the bike back under you and than lean the right way before you can hang against the gust. That is why these bikes make such distinctive wobbles in gusty winds.


>>Perhaps you refer to a reduced range of operation, where manipulated variable won´t get saturated and provided that the sail angle will not vary up to the point of loosing wind. I will try it.


Please note again that cats don't really need it, I only replied on how the skiff and moths guy are doing it. For them however there is no alternative. Also note that no skiff, landyacht or moth craft has a cleat on the mainsheet. The basis of the system is to win enough time to sufficiently depower the rig by other means. That is also why they have a kicking strap and not a not a mainsheet on a rail at the rear of the boom. They need the boom to run out swiftly. A big thing is also the weight of the boom. The lighter it can be made the better.

When you really want to know that hitch a ride on a 49-er skiff or any winged fast monohull without balast. Landyachting will teach you the same thing. Otherwise paying attention when you ride you bicycle in gusty conditions.

Wouter

OK, I got your point now, when you said "moving the weight out" you were talking about a design modification, not a control action, accompanied to other design modifications as well. The result of increasing rotational inertia (by that i mean integration of mass*radius, don´t remember well if it is called moment of inertia or rotational inertia or whatever) produces a slower system and thus enhances maneuvrability (is that a word?). I was suspecting that there wouldn´t be a cleat on the mainsheet too. So we are talking about a rather multivariable system here... the cat would be closer to a sinlge loops: trap for heel and steer for direction. I can even drink a beer on the trap if I would want to, that´s an advantage, isn´t it??
Hey I thought we were meant to forget all that dynamics crap after some time on the field, shouldn´t we??
Sail6000 I think you put some really interesting information there, thanks, I will just have to decode it a bit, too much terminology for a spanish speaker....

Greetings guys, nevermind if we are still talking on different frecuencies..

Yeah, adding larger wings so the skipper can move further out (in a static) way is one of these things. No human being can move out quick enough during a gust.




The real description is polair moment of enertia but I sort of slack on these things as otherwise 99 % of the reader would really not know what I'm talking about.

The equation is : increasing the polar moment of enertia => results in a system with a slower response to disturbing influences (gusts) => allows the human controller more or just enough time to think up (reflex really) and implement a control signal to bring back the system to a balance. => thus garanteeing a measure of maneuvrability.




Yes, that is true. Lucky for us the responses to each input are simple integrators with a dominant low order behaviour. 1st or 2nd order at the most). Note how dinghies can sometimes get into a death role which is a strong oscillary response that is beyond human capabilities to control effectively. This is one example of where the system is of an higher order than 2nd order. (2nd order is typically simple mass/acceleration/speed systems like driving a car etc, this is for normal readers)




it is very much the same system BUT one part of the response (Poles) is much more dominant in the whole setup than is the case in dinghies. Therefor you can more neglect the less important parts and totall focus on the dominant part (poles). So same system but with different parameter causing it to appear much more different to a human being.

To give a rough example. Remember how second order systems can cross over from overdamped to underdamped behaviour ? Where the first largely appears to be similar to a 1st order system while the underdamped system is clearly different with its overshoot and oscillary response. We may find that a similar thing is happening when going from dinghy to cats.

Afterall I've been in a death roll on 49-er but never on a catamaran.





Should that read " .. if we are all inside the same bandwidth ?"

Regards,

Wouter

See attachment for five foiled moth's flying off the line.

As the only one in the whole US of A who has tried this fun and exciting developmental change on cats, I feel somewhat qualified to comment. See www.fastsail.com/catcobbler for illustrations (no video yet)

Despite the somewhat overdesigned surface-piercing extruded aluminum hydrofoil sets that I have, they still work pretty well, and I have flown Hobie 18s, Hobie 16s and the little wooden-A cat seen in my thumbnail as a signature. Prindles next!

The images from Australia are wonderful. The 37 second 2-Moth clip of John (Ilett?) and Glen shows well the foiling process & how to fly at speed... The 9297 Moth in the foreground is going fast but rises up too high, loses lift and crashes as the skipper sheets out a bit, allowing the Moth with yellow trim to pass. But 9397 gets up again in a few seconds and accelerates to top speed to catch up. I do the same thing with a foiled cat, same process and the same fun.. Crashing is straight ahead and has NEVER resulted in a pitchpole in 5 years. You don't need to trapeze with surface-piercing foils either, as the foils lift the lee hull & keep the rig right side up.

Note some Moth sailors now complain that foiled Moths have ruined everything: the older Moths were little flat scows, and these scow sailors complained that new modern skinny balancing-act planing boats ruined their sport. Now some of these skinny-boat sailors are complaining that the foilers have ruined their sport. So- take a look at the Aussie pic of 5 Moths flying while coming off the start line and then tell me how their sport was ruined!

Discussion like this in the winter is great- lets hear more.
I don't expect much action from Americans anymore.... Somehow in the 21st Century, they want to stick with the store-boughten ol' TRIED and TRUE! I'm surprised that even a few carbon fiber masts are allowed here....we should all have oak planks & wooden masts on our racing displacement monohulls, and you can't beat stone ballast.

DAve CArlson

Winter? What you´re talking about! Sun is burning here..
Hey how about sharing some tips to build those cat foils?
Cheers