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Thank you very much Blunted,

Hope now, your leg is pretty repaired from your accident in Falmouth.

Torsion: Yes I am considering a Cogito style spar.

I am considering the "provocative" idea where a soft wing with 2 imbedded parralel spars, could lead to cheaper platform structure, I mean a large main crossbeam where all the big loads can be concentrated

so the hi-tec & expensive stuff can be concentraded too in this part of the boat, and the remaining can be bolted, without requirement to cook a full pateform in one piece.

A wing, with its CoE of  probably 10% to 12.5% ahead of a classic sail CoE,  will be helpfull for this concentration, (foils will move between mast foot and shrouds)

The best evidence is foiling C-Cat (all with wings), as you mentionned it, can make it with a bolted plateform.

Thanks again to have taken time to post interesting info about the loads and the "stress case" among other.

Best regards & Cheers

Erwan

 

 

 

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3 hours ago, Erwankerauzen said:

I am considering the "provocative" idea where a soft wing with 2 imbedded parralel spars, could lead to cheaper platform structure, I mean a large main crossbeam where all the big loads can be concentrated

so the hi-tec & expensive stuff can be concentraded too in this part of the boat, and the remaining can be bolted, without requirement to cook a full pateform in one piece.

Fun architecture. We do mostly the same thing on the UFO. One note: I have yet to see a c-class that wasn't bolted together. Co-curing or post curing all at once would be amazing to pull off purely as a technical feat but I don't know of any boat that was done that way. Before you progress much further with your project it would probably help to pick the brain of somebody who's built an ok one. That always helps flesh out configuration concepts.

DRC

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On 2/8/2018 at 7:18 AM, Shad34 said:

I had heard about Groupama not being very open with their design indeed... why wouldn't they share if asked by serious people?

I do not believe I am violating any copyright in posting these PDFs here.  I'll obey any credible take-down notice if I have erred.   It really was a golden age for C-sharing.  Kudos.

From the committee-boat I managed to snap blunted and fredo getting simultaneous Lake Ontario enemas (in Fig 3 of SteveK's paper).

Taking those shots, it looked like shock-loads were nasty even when just bobbing around waiting for the next start! 

Everything was all floppy, speed dead-slow, up comes a big wave, then... BANG. Ouch.

cheers
b2b
[Hmnnn, going to have to attach to next post, SA attachment size bug]

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On 2/14/2018 at 9:27 AM, Wess said:

Do you think the next fastest boat in the C class box rule is actually a catamaran and if not what shape do you think it takes?

I've wondered this, Wess.  I found this video interesting:

Not C, not at all definitive, not recent, but interesting.  I was surprised the kite+board pointed.  Reach? Sure.  But higher and faster to the windward mark?

enjoy

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On 11/7/2018 at 10:42 PM, Dave Clark said:

Fun architecture. We do mostly the same thing on the UFO. One note: I have yet to see a c-class that wasn't bolted together. Co-curing or post curing all at once would be amazing to pull off purely as a technical feat but I don't know of any boat that was done that way.

Thanks Dave,

Yes, you are perfectly right,  with the UFO, the loads transmitted by the rig to the plateform, are justsimilar to those of a wing sail.

By the way UFO is a very smart & innovative foiler concept, I have a special appeal to her foils with their elliptical leading edges. In addition, it is very affordable.

On 11/7/2018 at 10:42 PM, Dave Clark said:

Before you progress much further with your project it would probably help to pick the brain of somebody who's built an ok one. That always helps flesh out configuration concepts.

Well, I d love to find a similar sailing concept, but I cannot find one.

The idea is to use the same "structure" as a Cogito wing sail, I mean 2 spars:

The main one we are talking about, and a second parrallel one, positionned more or less at the same place than the trailing edge of element 1 of a 2/3 elements wing. (probably around 60/70% from the leading edge) to hold the leech.

I aim a soft and morphing single section instead od a 2/3 slotted wing. (6.5% max thickness  positionned between 15% and 20% of the chord) and max camber a little below 6% @ 15 % to 20% chord.

I might come in the C-Cat serie well before I can achieve something for an A-Cat.

Best regards

Erwan

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On 11/8/2018 at 11:29 AM, bacq2bacq said:

Super interesting! I am intrigued by the discussion re Rocker and how they found the combination of additional drag and depowered rig (to keep the boat flat) to limit its performance. The RM "lost" to the windward foil is part of the problem.

There's no mention of rake differential or increasing control surface on the foils. We use rake diff on the Whisper (with less rake on the windward foil), and sail with some windward heel. The Stunt S9 has comparatively large control flaps so I'd hazard that they create significant downward force. Both techniques work -- within limits -- to allow us to get more power out of the rig.

@Charlie P Mayer @flyinggorilla  -- might be of interest.

 

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On ‎11‎/‎8‎/‎2018 at 11:26 AM, ziper1221 said:

Are there any rule limitation on foils? Why does everyone use fixed foils instead of flapped (or solid, but hinged for AoA adjustment) with a wand that could automatically produce negative lift on the windward hull? 

Limits are that the foils need to be "inside the box", e.g. within the 14' beam rule. This is why Rocker was only 12' wide or so, we gave back some platform beam to ensure we could have T-foils under the boat still within the box.

Rocker, one more time, had flapped foils operated by wands.

No, we were not morons, of course we tried differential setups with the WW pulling down while the leeward pushed up. We tried three legged, we tried 4 on the floor, let the wands do what they want, we tried four on the floor, operate the windward flap manually to get RM out of it.

In the plus column, when on foils, Rocker was stable as anything I've ever sailed, rarely if ever pitched in, did not roll quickly at all etc. But over all our conclusion was there was simply too much junk in the water relative to Alpha. Yes we also tried the windward heel etc.

Perhaps we were not too smart. I mean we did get it to foil, in fact we got it foiling the first time we took it out in anger with a rig on it, in very little breeze. That was back before anybody figured out how you could use leeway to moderate heave and so really what we had were two moth's flying beside each other.

Good times.

Rocker-01.jpg.8daec4022da233c299c5af57e5da256a.jpgRocker-02.jpg.772495eec992c8ccf61f33280fd216d0.jpgFlight-sm.jpg.7450d612b1c97bbf2c87f590803931af.jpgRocker-03.jpg.456455136c86dccc54ee0a6875cbb0b8.jpg

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On ‎11‎/‎8‎/‎2018 at 11:36 AM, bacq2bacq said:

Half a second after Fig 3, fredo was heard to shout "THIS IS STOOOOPID!!"  Sorry, no audio...
 

IMG_6573.JPG

I remember quite distinctly that day thinking, "fuck we're going to break a forestay if this keeps up". Yes the conditions were bouncy and the rig and platform were all wriggly for sure. Front beam was flexing up and down quite a bit between races. Certainly settled down once we got to racing though. Memorable day.

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Re: Rocker

I wonder if Rocker influenced Michele's design of the S9.

Wand, foil and flap are remarkably similar to the S9.  Would be interesting to see how Rocker's hinge is built and how it works.

S9 cants rudder and main foil outward - but at different angles.  Is this dihedral or anhedral?  Why?

I don't understand when a fence (end plate?) works and when it just adds drag.  S9 has limit of 22 knots - would it be faster with shorter span and end plates?

 

S9 has little rocker and a square stern.  Seems immaterial when foiling, but seems draggy in very light displacement conditions, even with body weight forward of the front beam.

 

Tow testing:  tried it a few times.  Thrilled a couple of young Laser sailors last week - we now hand-hold the the tow rope - easier to bail out.

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1 hour ago, Charlie P Mayer said:

Re: Rocker

I wonder if Rocker influenced Michele's design of the S9.

Wand, foil and flap are remarkably similar to the S9.  Would be interesting to see how Rocker's hinge is built and how it works.

S9 cants rudder and main foil outward - but at different angles.  Is this dihedral or anhedral?  Why?

I don't understand when a fence (end plate?) works and when it just adds drag.  S9 has limit of 22 knots - would it be faster with shorter span and end plates?

 

S9 has little rocker and a square stern.  Seems immaterial when foiling, but seems draggy in very light displacement conditions, even with body weight forward of the front beam.

 

Tow testing:  tried it a few times.  Thrilled a couple of young Laser sailors last week - we now hand-hold the the tow rope - easier to bail out.

Top surface of the rocker foil is one piece, the part over the hinge IS the hinge. Below that there is a wedge notched out of the foil. On the bottom two flat bits slide past each other making it generally smooth. There is an arrow shaft or similar down the trailing edge of the vertical bit. A push rod travels through the shaft on the vertical bit and connects at the bottom to the flap with a wee little pin connection. 

I still have the main foil we cut off in 2007 laying about the house. I'll take some pics and vid some time for you.

Generally worked pretty well. Obviously the flap twisted somewhat as it was small and not super stiff, so the middle of the foil would always have more trim on than the extremities which was OK by us.

We also did two tow tests with Rocker before gambling a wing on it. We just added an extra body to make up for the mass of the missing wing. Unnerving at first, then quite comfortable once you got to trust it.

Like I said, we simply started by emulating the best moth technology at the time, easier then re-inventing all four wheels.

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@blunted My apologies for the repetitive question, prior to bacq's post the most recent comprehensive c-class paper I could find was from last century. I didn't mean to imply "why didn't these morons think of this" but rather what is the fatal flaw for why it isn't used, which the Alpha/Rocker paper does a good job of answering. I do have hope that the problems can be solved, but I don't know how much better than a non-foiling c-class hull you can get. 

Righting moment: a differential that works automatically, based on mast rotation. Possibly instead of using a flap that would require large amounts of tension and drag to keep negative lift, use a balanced system-- but there are obviously a host of problems there.

Lateral Resistance to Windward: The fact that Rocker preformed well with the foils cut down indicates that asymmetrical vertical foils are not strictly necessary, and a better control system keeping the optimal ride height could mitigate the leeway issue. 

 

I'm going to try it on a 3 point moth scow, we'll see how it goes

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Rocker could never point with Alpha due to the symmetric vertical foils on Rocker. So it always had about 3 degrees of leeway relative to Alpha, one reason it was slower upwind.

The hulls, The Alpha hull shape was awesome for displacement sailing, could only be outdone by Canaan. I will say this however, when landing at speed, e.g. coming off foils, you really would prefer a contemporary design with a lot of lateral area at the waterline, particularly in the bow. The nice fine bows that go so well in the light stuff do sweet bugger all to stay above the water when you fall off the foils. Its an express route to pitching it in if you're not careful. FYH was far more forgiving coming off the foils than the old Canoe like boats.

Differential based on mast rotation? you are breathing rarified air if you think you can link those two things without unintended consequences. As soon as you start foiling you about triple the number of links between forces on the boat. For example, if we were foiling and we happened to have some heel on, say 10-15 degrees, all of a sudden when you turn the rudder you are having big effects on pitch forces because now the vertical surfaces are creating vertical forces in addition to the horizontal forces. That little quick change in pitch all of a sudden can point the bow up a degree more than a second ago and bingo we have liftoff about 2 seconds later as the boat launches fully clear of the water then steps 20' sideways and crashes down. Damping heave response to match the mass of the boat and the skill of the sailors is important. That's the beauty of what ETNZ designed way back in 2013, it's largely self regulating and the regulation can be tailored to the mass and momentum of the boat as well as the speed and capacity of the crew to make trim changes. You'll never be quick enough on the hands adjusting foil rake to keep up with the scene, so it needs some form of self regulation, the smaller the boat, the faster it has to work.

Groupama had a safe setup for their foil geometry. The corollary was that they could sail the shit out of the boat with high degrees of confidence even if it was a bit draggier than less safe but more slippery options. On a boat with only two sets of hands there's a lot to be said for something that regulates itself in heave once gross settings are locked in. So their inside angle was something like 64 degrees on their foil which was the most conservative by 20 degrees at the event. Yes it cost drag, but it also freed them up to trim the wing and keep their head out of the boat and to sail. Keep in mind the crew is doing about 85% of the trim functions on the boat, adding the foils is another huge scope creep for crew tasks, plus the foiling foils are heavy and a lot of work to get up and down through each corner. My caloric workload in FYH probably doubled over a day on Canaan.

The flap control on rocker never had too much load on it. Look at how long the wand is relative to the opposite side of the rotation axis and you can see it has a lot of leverage to push and pull the flap. Sure, life is better without wands but wands are far lower loads to manage than raking both foils after each tack or gybe. 

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@blunted Mast rotation was just the first thing to come to mind for a mechanism to automatically tell what tack the boat is on. The whole point would be to automate the system, reducing crew load. Here is an example mechanism. This view is from above, immediately in front of the mast. The disk can rotate freely and move fore and aft. The red slider is locked pointed forward but can be moved left and right by the bar protruding from the mast. The forward hole attaches to the wand. The right hole attaches to the starboard foil, the left hole attaches to the port foil. 

 

First picture: The boat is head to wind, the lift on both foils is equal

head to wind.PNG

 

Second picture: The boat is on starboard tack. The lift on the port foil is increased while the lift on the starboard foil is decreased. The situation would be mirrored on port tack. The wand can still provide height information by pushing the disk fore and aft, it just provides that lift asymmetrically. 

starboard tack.PNG

 

Of course, this specific mechanism would only work upwind, since I would want less differential action after a certain amount of mast rotation, but this should give you an idea what I mean. @Doug Halsey Yes, but if this mechanism works out only one wand. I can't tell if he has T or L foils, and all the links I can find on that boat are dead. 

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11 hours ago, blunted said:

Damping heave response to match the mass of the boat and the skill of the sailors is important. That's the beauty of what ETNZ designed way back in 2013, it's largely self regulating and the regulation can be tailored to the mass and momentum of the boat as well as the speed and capacity of the crew to make trim changes. You'll never be quick enough on the hands adjusting foil rake to keep up with the scene, so it needs some form of self regulation, the smaller the boat, the faster it has to work.

Groupama had a safe setup for their foil geometry. The corollary was that they could sail the shit out of the boat with high degrees of confidence even if it was a bit draggier than less safe but more slippery options. On a boat with only two sets of hands there's a lot to be said for something that regulates itself in heave once gross settings are locked in. So their inside angle was something like 64 degrees on their foil which was the most conservative by 20 degrees at the event. Yes it cost drag, but it also freed them up to trim the wing and keep their head out of the boat and to sail.

@blunted -- your notes on what you tried on Rocker are gold. Thank you. Can you tell us more about the heave notes above. I'm not sure which mechanism or setup strategy you're talking about. 

(I agree on simple self regulating systems, just lost on which mechanism you're discussing re ETNZ and Groupama.)

 

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From a completely remote point of view, my thoughts are that Rocker failed upwind becaue it could not rely on sufficient windward heal to unload the verticals from lateral resistance duty. Moths then healed about 15deg but now more like 20deg. At this angle the windward component lf lift from the horizontal foil more than covers the lateral resistance loads and the boats actually climb to leeward, ie reverse leeway. It is very noticable how the boat slows when heal is reduced for manoevres.

The newer cat foils do this by having the hoizontal L or Z foils fitted at an angle to the horizontal about the same 20degs.

The other disadvantage is that the windward foils even if geared off are still providing a lot of drag for no real benefit. This still happens with most cats, even those which pull the windward foil up, but leave the  windward rudder down.

The scow foiler in the above photo was David French at the Perth 2016 nationals. The boat was reasonable downwind but hopeless upwind. I am on the boat with the yellow tramps on the second lap catching the scow which is on its first lap and I am deep in the mid fleet. I expect the Skeeta will perform more like a state of the art moth than the trifoiler.

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Skeeta has one main foil on the centreline like other moths. Well established and well developped configutaion.  If the foils and rig are good enough only the extra windage and weight of the scow hull are the negative.

 

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23 hours ago, martin.langhoff said:

@blunted -- your notes on what you tried on Rocker are gold. Thank you. Can you tell us more about the heave notes above. I'm not sure which mechanism or setup strategy you're talking about. 

(I agree on simple self regulating systems, just lost on which mechanism you're discussing re ETNZ and Groupama.)

 

The self regulating of heave is the V-foil configuration itself.

FoilRepair.jpg.e7a7601ea8cace91087a9fea1c13093b.jpg

Back before anybody understood foiling as we do today, as designers we'd all make the same first step which was the same mistake. We'd start with a vertical foil to keep the boat from going sideways and a horizontal foil to make it go up. In my Archemedian days I would tell you that leeway was a bug not a feature, I wouldn't want leeway because that's giving away pointing ability that we spent years trying to dial in to zero leeway on the course. 

In making that choice you somewhat separate lift and side forces making them almost discrete. Then you spend all manner of effort figuring out how to control lift. Darwin lead us to wands eventually as a good solution, just pick an alititude you want to fly at and make a mechanical system to force the foils to help you in that goal. But it still leaves a bunch of challenges particularly if you sail over a big range of boat speeds. On a t-foil you always have the same amount of foil in the water if you're going zero or 50 knots or at least up until you have zero foil in the water. So then you have to moderate and control, quite precisely, the lift out of a foil that barely changes shape and never changes size over a huge range of speeds. As such you are faced with making a bunch of compromises starting with your choice of liftoff speed. Want a low speed, you need a bigger foil, you chose bigger foils, congratulations, you get a slower top speed and a more flighty boat.

The V-foil configuration flips the script. The genius of it, and it took me more than a few moronic weeks to suss this one out, is that it turns leeway, that old bug, into a feature in the system. If we give up the C-class sacred cow of sailing through the water with no leeway for a second it opens up some possibilities. The most important of which is that the more leeway there is, the more it moderates the vertical lift of the two foils (I consider a V-foil to still be two foils, just happen to be connected). So as the whole show starts to slide sideways a little bit, one, degree, two degrees and so on, it starts becoming less "lifty" while still providing the side force you need. Double plus good is that as you go faster the boat lifts a bit higher and the area of the lifting foils also begins to moderate. This is important because it makes the foil less sensitive to small changes in pitch and far less likely to leap out of the water unexpectedly, which is exactly what a vertical / horizontal combo will do to you, repeatedly, ruthlessly with painful results.

So as leeway kicks in, because the boat is flying higher and has less available side force, it also begins to moderate lift and at some point you reach equilibrium of forces. then as an added bonus you remember that leeway doesn't matter any more at that point. why? Well because you're not dragging that stupid hull through the water any longer, you're flying it over the water so who gives a fuck anymore right? If you can't get pregnant who needs a condom? (Maybe there's a hole in that reasoning but we'll come back to STD's later). On a wing boat in particular upwind foiling leeway is a non-issue, you trim the wing to the AWA and nothing else. The bows would actually point more into the wind in this situation which is favorable form an aero-drag perspective.

So after all that, what did we get? We got equilibrium, that's the self regulating part of the system. An L-foil essentially cannot ever achieve equilibrium except in some kind of perfect steady state sailing. We did achieve that from time to time and it's fun and slippery but it's gone as soon as you change velocity, or any of a hundred other little things you could change on the boat intentionally or otherwise. Now some wag will come along and tell me how the modern AC50 boats essentially have L-foil systems and seem to do steady state sailing just fine, to which I say, "Sure, try sailing one of those in a straight line for two miles without any AOA input on the foils and see how it goes for you". In short, they use a never ending stream of AOA input to overcome the absence of equilibrium and instead keep many angels dancing on the head of a pin through hyper-exacting foil management which is simply not an option on a boat with only four hands available.

I should add that of course part of the system is to be able to change the rake of them, which is a big gross tune factor, and of course their roll angle or how they are trimmed inboard and outboard. The more you angle the foils in, the more aggressive the leeway effect is, but you trade away righting moment and things become draggier, but the ride is more stable. Thus foils are more upright upwind, when we sail in a narrower boat speed range and can afford less heave control, and they roll inboard when going downhill and we have a bigger dynamic range. The "inside angle" I was talking about was the angle between the "vertical" and "horizontal" parts of a V-foil. the smaller that angle, the more heave stable the boat will be but also the more draggy it will be. 90 degrees = sporting, 64 degrees = Franck sailing downhill at 28 knots in chop smiling his shit eating little grin, calm as the day is long. (To be clear, Franck is a cool dude, I respect him greatly and he did an awesome job killing us, I just got a bit fed up of our boat trying to kill us and seeing his transom all the time).

So the big development was making heave control intrinsic to the very foils themselves. Condoms optional.

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4 hours ago, blunted said:

The self regulating of heave is the V-foil configuration itself.

...

So the big development was making heave control intrinsic to the very foils themselves. Condoms optional.

It's so nice to hear V-foils referred to without all the usual negative prefixes. Of course, I'm not biased or anything :)

The pluses & minuses of the old-style V-foils (which attach at both ends) are debated further in this thread: https://www.boatdesign.net/threads/foil-cavitation-at-lower-speeds-than-expected.53927/

Blunted: Do you have any comparisons of how the boat behaves with the inboard tip above or below the surface of the water?

 

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7 hours ago, blunted said:

So as leeway kicks in, because the boat is flying higher and has less available side force, it also begins to moderate lift and at some point you reach equilibrium

That's a bit of insight I had not come across before. I had a much simpler mental picture of the equilibrium of V and J shaped foils (ie: less foil in the water). Thank you! 

On current a-cats, folks seem to have switched from J to Z foils, and making good process with them. I haven't wrapped my mind around the dynamics of Z foils. Has there been any C Class cats with Z foils? 

 

 

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16 hours ago, martin.langhoff said:

That's a bit of insight I had not come across before. I had a much simpler mental picture of the equilibrium of V and J shaped foils (ie: less foil in the water). Thank you! 

On current a-cats, folks seem to have switched from J to Z foils, and making good process with them. I haven't wrapped my mind around the dynamics of Z foils. Has there been any C Class cats with Z foils? 

 

 

Not to the best of my knowledge.

I'd never used them until I sailed on the TF10 this summer. I was lucky I spent a few days working with Pete Melvin on the boats. I explained I hadn't really wrapped my head around the dynamics of z-foils. He was kind enough to explain that they are essentially the same as a v-foil, you've just split the foil and moved it to opposite sides of the boat. I was admittedly skeptical but hey, he's spent far more time than me thinking about it so I went with that. Sure enough, it seems to work pretty much like he described. We were sailing one foil up, upwind, both foils down, downhill. Fun ride, gentle, nice landings etc. for flat out performance I'm not sure what would work better, in that case we were using the WW foil for some downforce so I would imagine it might be more powerful than straight up V-foils.

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19 hours ago, Doug Halsey said:

It's so nice to hear V-foils referred to without all the usual negative prefixes. Of course, I'm not biased or anything :)

The pluses & minuses of the old-style V-foils (which attach at both ends) are debated further in this thread: https://www.boatdesign.net/threads/foil-cavitation-at-lower-speeds-than-expected.53927/

Blunted: Do you have any comparisons of how the boat behaves with the inboard tip above or below the surface of the water?

 

not really? I mean with a tip that pierces that water it runs the risk of ventilation if its too loaded up and its more susceptible to ventilation the more horizontal the foil is, it seems. Invariably you'll get a bit more drag out of any foil at the water / air interface. Essentially lift is a bit of a write-off within two chord lengths of the surface of the water but again that could be a feature as much as a bug when you are trying to control for heave.

For me if I saw the inboard tip out of the water it simply meant the system was working. never noticed any global change in boat behavior.

Pretty cool if you have Mark Drela giving you input on your third post in a thread. Also a cool dude who most definitely knows his shit.

Me on the other hand, I'm taking off to BDA momentarily for a few days of libations and lead sleds, if things go well I imagine I'll have my tip just below the surface some time after sundown. Might end in a wipeout, we'll see what happens.

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On 11/14/2018 at 11:32 AM, blunted said:

90 degrees = sporting, 64 degrees = Franck sailing downhill at 28 knots in chop smiling his shit eating little grin, calm as the day is long.

Found this image in a technical paper about Groupamas foils and the V shown is ca 90 degree inside angle. Did they use other versions as the foil in the image you published is 64? But probably they didn´t want to reveal the correct angle in the paper.

Have had numerous discussion with Doug Halsey about V-foil "inside angles" and this has landed in the 60 to 75 degree region, with the V symmetrical to the surface.

 

Lars

Living in the epicenter of this catastrophic experiment:

"Thankfully Germany and Sweden are prototyping the latter experiment for us so we can see how Psuedo-socialist political structures work out when married to pathological altruism and presumably fleeing capital."

 

 

groupama.png.6e7cddd615d614d134ae4f976dcc3617.png

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On 11/16/2018 at 6:35 AM, revintage said:

Found this image in a technical paper about Groupamas foils

Link?  Or was that a limited quotation under "fair use"?  A reference for the threadsters, at least?  Please?

One day I'm going to have to scan in a copy of "Williwaw" by Dave Keiper.   Steve Killing, if you're out there: some day I'm going to drop by and pick that thing up!  Not C-class, but a hell of a foiling story.  The one thing ladders have over all else: simplicity!  Also: "Monitor" used back-stay tension to adjust front-foil AoA, I believe.  As the top of the mast drove forward, the backstay would increase lift at the bows...  https://www.boatdesign.net/attachments/baker_theflyingsailboat-pdf.142120/ 

Maybe we have found an optimum with various letter-shaped foils, but from my armchair I have to think there is a speed/stability correlation (as well as anti-correlation!): the more self-stable (esp in pitch) I would think the closer to the edge one could/would push... yes, that's it... close to the edge... down by the water...


ben

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  • 2 weeks later...
  • 9 months later...

Interesting article on the construction of Rafale II on JEC Composites site:

http://www.jeccomposites.com/knowledge/international-composites-news/rafale-ii-carbonepoxy-c-class-hydrofoil-catamaran

If only I had such facilities in my colleges (and that was at either the famed "Ship Science" course at Southampton University or at Imperial College, London where I was studying when I designed K-37)...

Really nice to see that this project is still running.

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Thanks for the link Rolandw,

Not sure I understand in depth the following:

To provide better aerodynamics and more speed, the ETS wingsail design includes a “morphing” trailing edge in the lower section of the rear part of the wing as well as the movable flap upper rear section. This morphing trailing edge section of the wing continuously changes shape and flexes in response to the applied wind force, curving slightly in a similar way to a flapping bird’s wing, which results in an increased forward thrust. Design optimization of morphing wing  aeronautical designs is a globally established research field, with ongoing projects investigating the design of next-generation morphing aircraft with improved flight performance.

The "Morphing" feature is interesting, but so far, remains a bit fuzzy for me

Extra details are welcome, if you do not breach your NDA.

Congratulations for this great achievement

EK

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Lindsay Cunningham's later rigs (particularly the double slot wing on the edge 3) had small flaps on the trailing edge of each section.  Primarily to generate a small overlap at each slot.  They also let them carry a lot more camber when required.

 

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Thanks SCARECROW, 

As it is mentionned:

This morphing trailing edge section of the wing continuously changes shape and flexes in response to the applied wind force,

So I guess to control the amount of camber, there is some limiting device.

The alternative would be to change the shape with a compliant mecanism, but if you let the wind make the job, you just need to limit the camber under the wind pressure, that is smarter. 

At least it is what I understand.

What is very surprising is the section of the mast/tube

120mm diameter seems very small, AFAIR, for the C-Cat Cogito it was something like 200mm diameter.

Is it the improvement in hight modulus carbon which makes it possible?

Cheers

EK

 

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"On current a-cats, folks seem to have switched from J to Z foils, and making good process with them. I haven't wrapped my mind around the dynamics of Z foils. Has there been any C Class cats with Z foils? "

Isn't this wrong to apply the requirements of a specific rule to general science. The A cats do this because they are restricted by the rule that days the board has to fit in the slot, no other reason.

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Check if the last Z22 or Z27 à EXPLODER A-Cat are Z shape??

I am not sure, but the DNA foils have a clear "kink" between the vertical strut and the lifting part of the foil

This clear angle at the junction  allows probably cheaper tools/moulds.

The EXploder instead seems to have a curved part to make the junction, probably a bit less draggy when in the water.

Not sure the J/Z concepts still relevant for A-Cat, Whatever the type of junction between the vertical strut and lifting surface, both design exhibits a +/-45° angle.

A Z foils like GroupamaC is more around 115°

Cheers

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A-Cat Z-foils essentially act like a J foil when they are used as a pair, i.e its like a split J board to some extent anyway. They automatically regulate heave, well reasonably so, and don't require tacking the boards like J boards so from that perspective on a small catamaran I think they make a ton of sense, regardless of the rule. The downside is reduced righting moment when going to weather, but you also have some savings from the weather board when foiling upwind as it prevents the weather hull from dropping into the water too quickly.

All things are a tradeoff, and despite the rules limiting foiling we have come to a good low drag, fast solution on the A. Right now the biggest request there is to allow the board to exceed the maximum platform width during insertion only (same as swing down rudders do currently BTW), as this would allow a maximum span board with a larger tip and less crazy S-bends. The larger tip helps with sideforce upwind while foiling.

On the C's, I would generally think that maximum stability is key. The rig inertia is a bit of a problem and having a stable foiling package ala Groupama C is key. Hydros was very 'jumpy' and I'm sure quite unsafe. Much has been learned about foiling small cats since those days so definitely a faster package than Groupama C could be built, but I also suspect it would be cheaper to start with a boat like Groupama C and fit an updated foil package.

The $ side for foil development is what has led to there being 2 main A-Cat builders at present, though the Scheurer G7 was 8th and 14th in Weymouth so is also a contender IMO, just limited production. They are lucky as one of the partners is a CFD guru. To get the C's going again I would think a standard platform/rig with a large box for the foil trunk to be installed in would help a lot, but some wealthy individuals would need to step up to fund the class similar to the 18 foot skiffs.

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34 minutes ago, samc99us said:

All things are a tradeoff, and despite the rules limiting foiling we have come to a good low drag, fast solution on the A. Right now the biggest request there is to allow the board to exceed the maximum platform width during insertion only (same as swing down rudders do currently BTW), as this would allow a maximum span board with a larger tip and less crazy S-bends. The larger tip helps with sideforce upwind while foiling.

 Hi Sam, the inward foils on the A-cat could surely be bettered if the rules where changed. As I am not sure exactly what your ideal A-cat foils would look like, do you mind drawing a few lines to show?

Brgds

Lars

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Hi,

Thanks Sam, for this crystal clear sum up.

It is a nice discussion, although more A-Cat than C-cat oriented.

After the World, a well known catamaran website, published some comments regarding the max width rule for the rudder T foil and the main foil too.

It could be an opportunity to create a dedicated thread about The future of A-Cat and why not C-Cat,

including all potential improvements within the existing rules.. or ... not.

A kind of brainstorming, like usual discussions after the races,

The big difference is that everybody will have to prepare his own fresh beers.

Cheers

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I think for most foilers, keeping the t-foil rudder inside the span limits damage to sailors during falls.

Are there any updated to existing C-class boats? Where are the Hydros platforms? I hear Groupama was in the middle east and destroyed. Is there interest in putting these rides back on the water?

The Easy to Fly looks pretty similar to Groupama C, Steve Clark thinks they might be the same molds. 150k euros for the ready to sail boat. Not too bad, but I wonder if lighter platforms with up to date foils could be made available, for custom rigs? I'm thinking that the latest AC75 style rig could work on a C, not as efficient as the wing sail but a lot less hassle to move and maybe a 85-90% solution?

 

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Sam,

Your remark regarding the security & T foils span is very relevant, and I should have guessed it as not long time ago Franck Cammas had is feet seriously damaged by a rudder TFoil.

For the C-Cats I have the same infos than you.

A double skin wingsail could be a cost effective solution to put C-Cats on the water, watching Hydros on a capzise at Falmouth 2013, you could see the (rear) flap exploding (before to touch the water) when the wingsail (front) was crashing in the water.

A single double skin wingsail might lack "Torque" compared to a slotted 2 /3 elements wingsail

at full speed no problem but to achieve this speed, it might be longer with a single surface wing.

Fair Winds

EK

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EK,

  Rig size could also potentially be increased some to counter the lost "torque" (drive) of the 2 or 3 element wingsail.

  Any word on what happened with the German C-Class? Or their A-Class development? All seems to have stalled...the expertise required for foil development I think is a big hurdle these days, where easily $500k could be spent on tooling and fabrication alone.

 

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2 hours ago, Doug Halsey said:

Some of you might be too young to remember the 1978 Little America's Cup: 

Even if you are too young to remember the Italians (also Signor G) there have been later boats that have adopted a much simpler wing concept in order to save weight (and complexity and cost) and have been remarkably close to proving their point. Now that speeds have increased with foils, the demand for pure grunt going downhill will have diminished leaving efficiency more important (think closer to gliders than to a 747 in take-off mode). The potential for simple, flexible wings is greater than ever and, interestingly, not nearly as complicated today as Miss Lancia's grand-piano control box implies.

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The North American A-Class Trophy is one given by Tony DiMauro.  He visited Lake Hopatcong, NJ in the early 60s and the story is that he was so impressed that he had his wife go get a silver cup in NYC to make a trophy that we have used ever since. She must have indeed been a very Patient Lady.

 

 

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AFAIR The soft wing used by Miss Lancia or Signor J, had a great drawback according to the designer:

He mentionned that the "Symetrisation" of the leading edge ( compared to the asymetric wing section's model/benchmark,) was very dammageable to the performances.

I have the newspaper somewhere in my archives, but don't know where, sorry.

Fair Winds

EK

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On 9/27/2019 at 3:35 PM, samc99us said:

 

  Any word on what happened with the German C-Class? Or their A-Class development? All seems to have stalled...the expertise required for foil development I think is a big hurdle these days, where easily $500k could be spent on tooling and fabrication alone.

 

An update on the German C Class (Alpha) and the A+ development....

The German Team disbanded after Geneva, as key members moved in different directions, Italy and Spain.  Alpha is stored in Italy and up for sale (we hopefully have someone interested in taking up custodianship of this special boat).  The A-Class project became a wing rigged scale model of a C-Class (the A+) using an A-Class hull tool.  This boat is now based in Mar de Cristal in Spain, where this 'Key Member' retired to.  Sito Avriles and myself are still developing the boat and we have my old Balance A-Class to try out foiling options before risking the wing on the A+.  As Sam mentions though, tooling changes and materials to accommodate new ideas are expensive.  Access to good CFD has helped here.

EK's comment on the symmetrical LE on the Italian C's is really a function of the thickness of the LE section, no slot and the need to achieve high alpha values downwind with a displacement boat, where an asymmetric LE would be of benefit.  As Roland has mentioned earlier and we have seen with the AC boats, a symmetrical D section mast as part of a relatively thin section doesn't appear to hamper a foiling boat where the high camber downwind grunt isn't required.  The idea of a mini AC rig does have appeal.... especially if it can be kept relatively simple (and light).  Controls need to be kept simple, as my much younger brain nearly exploded when I saw the interior of the Italian wings!

 No quite stalled, but in the buffet......

John D   

BPS_4106.jpg

IMG_1046.jpg

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Thanks Desert Wings for this update,

Very interesting project your A+Wing, Does the first element twist ?

The design of the wing looks great, Even if I get a little idea of it, with the picture above, I would  love to see the outline of the wing / side view. I would love to have the figures if not a secret.

Fair wind and best wishes for this great project

EK

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Thanks. 

The hounds are a bearing supported tube, concentric with the mast tube.  Principly to allow consistent rigging tension and reduce torque effects, hence the cutouts.  Planning to fit a membrane seal around the rigging when we get around to it!  The cutouts do reduce buckling issues in the LE though.

The boat is actually an 18 Square near enough with a 10ft beam, so we haven't compared with a soft A Class rig directly, just built as light as we could......

Building the wing has certainly stimulated ideas for a simpler (lighter) rig for an A Class in the future.  But as you said in an earlier post, experimentation isn't cheap with these materials!

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Thank you for these very interesting pictures.

I love the elliptical outline (or sailplan shape) of your wing.

Also the picture from behind clearly shows the flap trailing edge flexion (under aero loads) which is more curvy in the bottom and hence is likely to match perfectly the apparent wind twist.

I guess that, just behind this tiny piece of carbon, there is a lot of work. 

First element twist is also noticeable on this picture, and I don't know if it is an illusion or reality, at the bottom of the wing, I almost can see some marginal "bending" in the first element trailing edge and flap's leading edge?

As your wing is probably above the A-Cat's 150 sq feet, I feel confident that a shorter one, made with the same tools (moulds) would make it perfectly.

It could be interesting to know which area can be achieved with a 8.5 meters span for instance,

or which span is necessary to get the 150 feet aera?

In addition, a shorter rig with shorter spars, with less righting moment and less sail area is likely to lead to a more than proportionnaly lighter wing, I mean  20% smaller sail area could lead to a 40% lighter wing. 

Congratulations again for this great achievement;

It might deserve its own thread

EK

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Doug Halsey, September 27,

That article is still in my files.  It was very influential in getting me interested in sailing C Cats.  I think I was interested in the class at the prior challenge, but I have no proof in my files.  They start with that article.  I promised myself that "one day, I will sail one of those boats."  Was it ever worth it.

Thanks for reminding me of great days as a kid, looking forward to that "one day" in the future.

Best regards,

Fredo

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  • 4 months later...
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12 hours ago, Steve Clark said:

C Class has gone to sleep, possibly for ever.  There are no projects that I am aware of. I assume that everything is for sale.

SHC

It's sad, but that's movement, there will only ever be so many people playing with this stuff, and it seems those people are really spread through other things.

I used to walk past an old C Class at a local club and think "fuck me, instead of leaving it to rot, give it to me, I'd love to play with that". It was the Ronstan one, which every week looked... a little worse :(

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Shad 34 et al,

I’m retired, oldish and fully committed to our A+ programmme, so here we go:

Alpha is still available....would love to find her a new custodian.  The ad has expired, but PM me if you are interested.  Box trailer included.

She is part of C Class history and doesn’t deserve the same fate as Ronstan.......

Near Bologna in N Italy.

 

 

 

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10 hours ago, PL3 said:

Check "thebeachcats.com" classified for the best deal ever on a C. 

https://www.thebeachcats.com/classifieds/catamarans-for-sale/p16833-25-27-cat.html

$4,500 for PLIII

Not much detail so unless you know your C Class history you won't understand the significance of this ad. Might be an easier sell if PL3 were to add a better description!

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Further to my post above, I have a clear conscience now I have purchased an AD!

If you are interested in a Wing-Rigged C Class, Alpha is available!  She was commissioned from Steve Killing by Fred Eaton, winning the Cup in 2007 helmed by Fred and crewed by Magnus Clarke.  She has been sailed by many great sailors during her distinguished career.....notably Glenn Ashby and Jimmy Spithill giving Fred and Magnus a run for their money in the 2010 Challenge.

She has been stored in her bespoke box trailer since the 2015 Little Cup (where she won a race).  The trailer is located near Bologna in Italy.

As I mentioned above she deserves a custodian who appreciates her history!

PM me if you have any questions....

Paul Larsen (Sailrocket) sailing below

IMG_1753.JPG

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Thank you so much for your answers, Steve, Multihuler and Desert Wings.

Let's hope that, like the phoenix, the class will be reborn from its ashes soon.
For my part, I still have to find a clever way to perhaps succeed in financing such a boat. It would be such a blast!

Cheers,

PJ

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On 9/2/2020 at 3:29 AM, Desert Wings said:

Further to my post above, I have a clear conscience now I have purchased an AD!

If you are interested in a Wing-Rigged C Class, Alpha is available!  She was commissioned from Steve Killing by Fred Eaton, winning the Cup in 2007 helmed by Fred and crewed by Magnus Clarke.  She has been sailed by many great sailors during her distinguished career.....notably Glenn Ashby and Jimmy Spithill giving Fred and Magnus a run for their money in the 2010 Challenge.

She has been stored in her bespoke box trailer since the 2015 Little Cup (where she won a race).  The trailer is located near Bologna in Italy.

As I mentioned above she deserves a custodian who appreciates her history!

PM me if you have any questions....

Paul Larsen (Sailrocket) sailing below

IMG_1753.JPG

There is just something about a C-Class...

They are so bad ass!

 

 

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Two years ago we dragged Aethon USA105 out of moth balls to sail with the ETS team in Montreal. They were the only ones doing anything and I thought we should give them a race.  I got on the boat for the first time since Geneva in 2015 and set off down the Kickemuit is an odd North Easterly breeze. About half way to the Narrows we got a puff, and it was like:

OH     I REMEMBER THIS DRUG    MOTHERFUCKER THIS IS SWEEET!

The designation A B C & D classes were created by Beecher Moore and the RYA to bring the minimum structure to the development of sailing catamarans in the late 50’s.  Length, beam, sail area and number of crew were the only restrictions,  The B Class was the most popular, but development stopped when the Tornado was selected for the Olympics.  There never was much action in the D class, the most remarkable being Steve Dashew’s Beowulf. The C Class was selected for the International Catamaran Challenge Cup ( also called the Little America’s Cup in the days before trademarks and lawyers took everything so fucking seriously) and it was expected to drive the development of racing catamarans.  It achieved this and more.  Almost every advance in catamarans was tried and proven in the C class before it went public. The best C Class Catamarans are remarkable sailing machines.  Bad C Class exist and are far too much like what most people call catamarans.  They lived and died with only seven rules ( and there was NO RULE 6!)    So there was enough freedom to actually try new things, like wing sails, and advanced materials. The AC 72 and the still more remarkable AC an F 50 catamarans would not exist if a relatively small number of people hadn’t built the 200 or so C Class that came before them.

The only survivor of the “letter” class catamarans is the A class. They are healthy and continue to push the envelope of Catamaran development but within a more restricted design space, so while they provide great sport, their opportunity to advance the knowledge base is more limited.

I try to put a good face on it, but I do feel that something valuable has been lost.  It’s a hard claim to make because while we had some fans, there really never was a base of people who saw the value in the class or thought participating offered enough prestige. Certainly it wasn’t cheap and it wasn’t easy but people spend that amount of money doing all sorts of stupid things.  Sometimes in great numbers. By serious yachting standards, the costs were modest although as Franc Cammas said “ they were disproportionate to the size of the vessel”  So I sit and wonder what to do with the contents of Clark’s weird shit tent. (Patiebt Ladies IV &V, Cogito, Aethon, and Orion, and two and a half wings)  I haven’t gotten to giving it away to numbskulls who will use it until they break something ( probably within the first two weeks) and never put it back together. And I haven’t got the nerve to crush it into a dumpster,  

SHC

 

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13 minutes ago, Steve Clark said:

Two years ago we dragged Aethon USA105 out of moth balls to sail with the ETS team in Montreal. They were the only ones doing anything and I thought we should give them a race.  I got on the boat for the first time since Geneva in 2015 and set off down the Kickemuit is an odd North Easterly breeze. About half way to the Narrows we got a puff, and it was like:

OH     I REMEMBER THIS DRUG    MOTHERFUCKER THIS IS SWEEET!

The designation A B C & D classes were created by Beecher Moore and the RYA to bring the minimum structure to the development of sailing catamarans in the late 50’s.  Length, beam, sail area and number of crew were the only restrictions,  The B Class was the most popular, but development stopped when the Tornado was selected for the Olympics.  There never was much action in the D class, the most remarkable being Steve Dashew’s Beowulf. The C Class was selected for the International Catamaran Challenge Cup ( also called the Little America’s Cup in the days before trademarks and lawyers took everything so fucking seriously) and it was expected to drive the development of racing catamarans.  It achieved this and more.  Almost every advance in catamarans was tried and proven in the C class before it went public. The best C Class Catamarans are remarkable sailing machines.  Bad C Class exist and are far too much like what most people call catamarans.  They lived and died with only seven rules ( and there was NO RULE 6!)    So there was enough freedom to actually try new things, like wing sails, and advanced materials. The AC 72 and the still more remarkable AC an F 50 catamarans would not exist if a relatively small number of people hadn’t built the 200 or so C Class that came before them.

The only survivor of the “letter” class catamarans is the A class. They are healthy and continue to push the envelope of Catamaran development but within a more restricted design space, so while they provide great sport, their opportunity to advance the knowledge base is more limited.

I try to put a good face on it, but I do feel that something valuable has been lost.  It’s a hard claim to make because while we had some fans, there really never was a base of people who saw the value in the class or thought participating offered enough prestige. Certainly it wasn’t cheap and it wasn’t easy but people spend that amount of money doing all sorts of stupid things.  Sometimes in great numbers. By serious yachting standards, the costs were modest although as Franc Cammas said “ they were disproportionate to the size of the vessel”  So I sit and wonder what to do with the contents of Clark’s weird shit tent. (Patiebt Ladies IV &V, Cogito, Aethon, and Orion, and two and a half wings)  I haven’t gotten to giving it away to numbskulls who will use it until they break something ( probably within the first two weeks) and never put it back together. And I haven’t got the nerve to crush it into a dumpster,  

SHC

 

I have been looking for the perfect location for a multihull museum, a lake with a grass shoreline would be nice, lake Champlain, Toronto or the Beaufort area are in the running,  if you ever decide to clean the shed, I would throw some money your way. And anyone that has an idea of the perfect body of water please let me know.

Of course documenting the history along side the superships would be a prize

Cheers,

Stephen 

R2AKTEAMGOLDENOLDIES 

 

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The idea of a museum seems excellent to me, indeed, knowing the complexity of care and maintenance of these boats. An amateur, even an enlightened one, would quickly be unable to maintain the boats in a good racing condition (at least the wing, the idea of finding a classic rigging is an interesting one), and it would be a loss for all.

What about the Herreshoff museum in Rhode Island ?

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8 hours ago, Steve Clark said:

Talked to Herreshoff. They don’t have room.

SHC

That's too bad, Steve, it would have made a lot of sense.

I figure you also talked to the museum of yachting in Newport ?

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  • 11 months later...

I don't knw if anyone will answer this....

I found the Patient Lady 3 for sale in CT in September of 2021. I bought her. I am interested in finding out if there are any C-Class Catamarans still in existence. Please comment on the existence or non-existence of other boats.

Thank you

Captain Chris

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 I brought a house in Washington NC, where I will bring my fleet, 2 Formula 40s, soft wing c class and a Newick.

There will be  fund raising to support a multihull race/ gathering. Pitching it to the city, including a shrimp cook off, fly in , and sail in. Should be fun.

Also looking for that museum location, how cool it would be if it became a stable of C class boats.

Anyone and everyone is invited to sail the F40 Skateaway,  100% of proceeds will go to the event.

Cheers, 

Stephen 

Resized_20211010_172232(2).jpg

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17 hours ago, chrisoptics said:

I don't knw if anyone will answer this....

I found the Patient Lady 3 for sale in CT in September of 2021. I bought her. I am interested in finding out if there are any C-Class Catamarans still in existence. Please comment on the existence or non-existence of other boats.

Thank you

Captain Chris