TheGaragista

Building an A-class Catamaran

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Hey everyone, I’m looking to build a foiling A-class catamaran, and I’m looking for advice and building plans. I’ve seen John Lindahl’s method of building a half female mold and I intend to do the same. Any advice is helpful, and I’m also looking for plans. Thanks

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That’s a complex task. Unless you like spending a long time in the shed building something that will be out of date by the time you finish it - just buy one from Jakub. You’ll save a lot of time, probably a lot of money and it’ll most likely sail a lot better. 

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Or buy 2hand (they're pretty cheap). Then you can try all you ideas and you are getting all bits and pieces along for a lower price and way less time wasted (boats are the best way to waste time though:-)  

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Thanks everyone for their quick responses. I currently own an old Flyer A-cat. I want to build a catamaran for the experience and to learn how, not really for cost reasons

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I was going to have a crack at this too using a mast and foils from a current manufacturer because the development work needed on these parts is enormous. The cost of these parts alone is enormous too which is what put me off. 

I think that the hulls of these boats will become more and more superfluous as development goes on. So i was was going to use a spine in each hull to join the beams, foils and forestay and then fit the hull halves as ultra thin skins around this - almost like fairings. The hull would not be part of the structure.       Sooo much to go wrong here, Its more of a design exercise than an attempt at winning races

 

I also think that trapezing will become redundant - too much windage. The skipper will end up tucked in between the skins of the tramp and the foils sorting out the righting moment.

 

 

 

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1 hour ago, teamvmg said:

I also think that trapezing will become redundant - too much windage.

Very relevant remark

So easy to calculate crew aero drag & compare it with total driving force

But IMHO  moving the crew weight "inside the tramp would kill the righting , I think it could be easier to suss out a NACA 33% relative thickness sailing suit, with kevlar ribs and possibility to switch LE & TE for each tack or gybe.

One must not forget the parasitic drag from the wires (48 meters * 3 mm diameter & drag coef between 0.8 & 1).

With 30 knts apparent wind, sailing windward on the foils, these parasitic drags are significant & remain the only ones that can be addressed for cheap.

Crunching roughly a few figures, you might find that the total driving force is somewhere between 170 Newtons & 250 Newtons

Trapezing crew 's drag around 30/ 35 Newtons

Wire's parasitic drag around 15/20 Newtons.

Very rought idea, but better than nothing.

My best wish for your project Garagista,  while the price for a garage in NY to build your A-Cat ....

well you see what I mean.

Cheers & Happy New Year

E

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Haha Erwan don't worry, I live on the Island and I have a very suitable garage to work out of. So no one is aware of any commercially available plans?

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If you wanted to start with something more than foam shaping, you could get in touch with Steve Clark who I think has DK17 molds in Newport or these folks for some help: http://www.openwatersyachts.com/A-Class-Cat.php.  

Could also reach out to Matt McDonald at Falcon Marine in Florida who may still have some things from when he built A-Class.  OH Rogers likely has some molds as would Ben Hall.

Tony Arends is a master of the Lindhahl method.  His last custom boat is very innovative, but he has moved back to Australia.

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Since 1986 I have been interested in A-Cat, the only available plans I can remember were for plywood construction with developable surfaces, not far from the Tornado original plan.

 

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I forgot:

A Canadian University is building a C-Cat catamaran,  you can ask if they can provide you with their hull plan, and you just have to reduce it to your size.

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14 minutes ago, Erwankerauzen said:

I forgot:

A Canadian University is building a C-Cat catamaran,  you can ask if they can provide you with their hull plan, and you just have to reduce it to your size.

AWESOME!! This project actually started out as me wanting to build a C-Class catamaran, but I realized that there couldn’t possibly be any plans. Thanks, and I now want to build a C!

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You jumped straight past B !!

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I believe Tonys Predator hull molds are available. The shape is very good for either a floater or foiler, very similar to the DNA C board boats, a little less volume which is also good for a foiler IMO.

Unfortunately you can’t match the stiffness to weight ratio of a production build without an oven, and if this is your first real composites project I would pass on Nomex. Beams require high modulus carbon, I can help with U.S sources.

Don’t try and build your own foils. They will likely break, and not be nearly as good as current production boards. I would instead find a used set of Z22’s (I know where some are...) and buy a set of cassette rudders. Budget $4500 for foils alone.

Also, don’t underestimate your time. Just fitting foiling boards and rudders to my Flyer was a 160 man hour job by composites professionals. This does not including rigging the slider mechanism and the rest of the boat which is easily another 160 hour job.  A modern A Cat requires close to that from the factory with all the adjustable systems (I can rig a 3 sail F18 from bare beams faster). Fortunately both builders have stepped up to reduce that for the customer at increased cost. You would be better off buying my conversion (professionally done by Tony and myself) if you wanted to sail. If you want to build, I might suggest starting with putting C boards into your flyer and seeing if you really want to build. At the end you would have a competitive classic boat for a fraction of the cost of the materials for one half of one A cat hull.

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^^^ This is good advice.

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18 hours ago, Erwankerauzen said:

 

Since 1986 I have been interested in A-Cat, the only available plans I can remember were for plywood construction with developable surfaces, not far from the Tornado original plan.

 

I'll bet those involved tortured-ply, not developable surfaces. There's a big difference in the skill involved to build them!

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19 hours ago, TheGaragista said:

AWESOME!! This project actually started out as me wanting to build a C-Class catamaran, but I realized that there couldn’t possibly be any plans. Thanks, and I now want to build a C!

I've seen the Canadian C class. Has a wing. Boat and the team behind it participated in Foiling Week Miami 2018. They're in the event videos, and probably their talk is on YouTube as well.

It's a big toy. You need a dozen people and a chase boat to prep, launch, sail in champagne conditions -- weather, facilities, etc.

I can tell you want to build, but unsure whether you want to sail your creation. If you do plan to sail it, an a-cat sized boat is more reasonable wrt logistics.

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TheGaragista,

Very good advices above

Franck Cammas comments, regarding his C-Class GroupamaC, was that these boats require a amout of care that is not commensurate with the boat.

He never went out without a nany boat with at least 250hp, very climate friendly!:(

But if you want, Similar hulls & cross-beams are available in France, near Lorient I think.

Good Luck

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23 hours ago, Lost in Translation said:

If you wanted to start with something more than foam shaping, you could get in touch with Steve Clark who I think has DK17 molds in Newport or these folks for some help: http://www.openwatersyachts.com/A-Class-Cat.php.  

Could also reach out to Matt McDonald at Falcon Marine in Florida who may still have some things from when he built A-Class.  OH Rogers likely has some molds as would Ben Hall.

Tony Arends is a master of the Lindhahl method.  His last custom boat is very innovative, but he has moved back to Australia.

Has anyone raced the Openwaters catamaran? The custom mast and hard deck are interesting for sure. I can see the hard deck getting closer in weight to the tramp+beams if you went to a lower weight rear beam then what has been used to date, and the aero benefits are probably real (see moth hard wing sails). However it is hard to beat a high modulus carbon tube for strength+stiffness, so overall I still see this platform as 10-20lbs heavier than a production boat. Still, good on the designer/builder for actually giving it a go with what appears to be quality bits across the board.

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On 1/9/2020 at 8:40 AM, teamvmg said:

I was going to have a crack at this too using a mast and foils from a current manufacturer because the development work needed on these parts is enormous. The cost of these parts alone is enormous too which is what put me off. 

I think that the hulls of these boats will become more and more superfluous as development goes on. So i was was going to use a spine in each hull to join the beams, foils and forestay and then fit the hull halves as ultra thin skins around this - almost like fairings. The hull would not be part of the structure.       Sooo much to go wrong here, Its more of a design exercise than an attempt at winning races

 

I also think that trapezing will become redundant - too much windage. The skipper will end up tucked in between the skins of the tramp and the foils sorting out the righting moment.

Re ultra thin skins:  Sitting around waiting for the next race at Miami the last 2 years, slamming pretty hard in the chop, and wondering how many fatigue cycles the bow is going thru.  MAYBE you can get up above it when you are actually sailing, but these hulls get worked pretty hard...

 

 

 

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On 1/11/2020 at 12:12 AM, Bsquared said:

Re ultra thin skins:  Sitting around waiting for the next race at Miami the last 2 years, slamming pretty hard in the chop, and wondering how many fatigue cycles the bow is going thru.  MAYBE you can get up above it when you are actually sailing, but these hulls get worked pretty hard...

 

An A-class only needs to be 10 foot long in the water, the bow is just there to hold the mast up and won't need to be buoyant once drag is cut down so much that they will foil in any breeze.

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You still have to get airborne, period. The Swiss already showed that while possible, I-beam construction + thin skins isn’t practical, and t-foils are much easier to foil in light air. That isn’t to say A cats are hard to sail in the light, they just require pumping to get airborne like many foiling craft and having some non zero hull volume is a big help...as is being able to go waaaay forward and get the transom in the water in light air as seen in the photos from Weymouth.

Also, from a pure structures perspective, a hull is pretty good as box beam structures are stiff, good for foiling. I think there is some room for a better beam/hull/foil connection  approach, but this has a lot of torsional load. Right now the weakest link is the lower foil bearings (should pivot IMO) and the rudder cassettes on the eXploder. DNA have solutions for both of these but there are other trades, and I’m not yet ready to switch platforms for these two relatively minor issues.

I did track down the Predator hull molds if those are of help/interest.

 

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In your construction process, before to start, check if you can get the carbone you need at reasonnable price.

I have been investigating Air Flow Spreading, in order to make my own thin-ply, but unfortunatly, Toray will never sell me a few spool of T1000 and I will have to buy lower modulus, from less established brand and with specs that do not match Toray's specs.

Good Luck anyway

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Your best bet for thin ply is carboweave or Textreme. Both are available in higher modulus formats. Trying to make your own spread tow fabric is not trivial and won’t save much money. The money saved is in the process used to make your own prepreg, which is to wet the cloth out between two sheets of plastic drop cloth with a squeegee, meticulously, and minimize the resin used to get a wet carbon. This is tricky as carbon looks the same dry as wet. It is also tricky as some binders used take a really long time to break down; I have been most happy with Carboweave and have tried other clothes with less success. 

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26 minutes ago, samc99us said:

Your best bet for thin ply is carboweave or Textreme. Both are available in higher modulus formats. Trying to make your own spread tow fabric is not trivial and won’t save much money. The money saved is in the process used to make your own prepreg, which is to wet the cloth out between two sheets of plastic drop cloth with a squeegee, meticulously, and minimize the resin used to get a wet carbon. This is tricky as carbon looks the same dry as wet. It is also tricky as some binders used take a really long time to break down; I have been most happy with Carboweave and have tried other clothes with less success. 

I've done a bunch with the textream, including bagging it to glue film to preg it, and have been very happy with the quality and results. Its a good fabric. 

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SAM,

Thanks for info, I will check Carboweave.

You are right, A dry Zoltek 50g/sqm is about 132€/kg while a Prepeg T700 100g/sqm is around 500€/kg. (both are around 240Gpa/4500Mpa/1.5% 2%)

TeXtrem Hight Modulus (455Gpa/400Mpa/1%) in dry tape 20mm wide  is around 1070€/kg

So I cannot imagine the price when prepeg.

20 hours ago, samc99us said:

It is also tricky as some binders used take a really long time to break down;

By "Break down" do you mean binders does not dissolve correctly into the epoxy during the impregnation process?

Sorry if the question is a bit candid, I am a bit rookie with these matters.

Cheers

 

 

 

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23 minutes ago, Erwankerauzen said:

SAM,

Thanks for info, I will check Carboweave.

You are right, A dry Zoltek 50g/sqm is about 132€/kg while a Prepeg T700 100g/sqm is around 500€/kg. (both are around 240Gpa/4500Mpa/1.5% 2%)

TeXtrem Hight Modulus (455Gpa/400Mpa/1%) in dry tape 20mm wide  is around 1070€/kg

So I cannot imagine the price when prepeg.

By "Break down" do you mean binders does not dissolve correctly into the epoxy during the impregnation process?

Sorry if the question is a bit candid, I am a bit rookie with these matters.

Cheers

 

 

 

Yes, that is what I mean by 'impregnation'. Early batches of the fabric do not allow proper fiber penetration when used in thin laminates (i.e single or double laminates) under conventional vacuum bagging. Keep in mind that the test coupons spelled out by Textreme are in autoclave environments with a 20 layer stack. This is very different to their end use case in a high performance application. That being said, I have a feeling they fixed the binder. I also think Carboweave and similar materials are stronger. The Textreme tapes are very nice though, a hard product to beat as they don't have loose fiber strands common with most uni carbon tapes, and are available in higher modulus and lower weights than pretty much any other commercial product.

R&G composites in Germany is your best bet, if they don't list it they can get it...carbon isn't cheap regardless of where you shop however!

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On 1/10/2020 at 12:40 AM, teamvmg said:

I think that the hulls of these boats will become more and more superfluous as development goes on. So i was was going to use a spine in each hull to join the beams, foils and forestay and then fit the hull halves as ultra thin skins around this - almost like fairings. The hull would not be part of the structure.   

I think this is so wrong. The hulls have to be part of the structure because of the twisting forces. Consider the centreboards and their cases. They are trying to "rotate" and need the bulkheads and the hull skins to resist that force. Bulkheads and a spine would never manage to resist the forces on their own. Same with the loads on the transom - rotational and pulling. Transoms have been ripped off. Then look at a top A from behind and you would be surprised at how much twist you see in the platform.

When you do the structural analysis, there is a minimum size of hull needed for structural purposes, even with spines, beams and bulkheads. It should be noted that the strongest, lightest and most twist resistant platforms ever made were monocoque hulls made by Marstrom with no bulkheads or spine at all. By using all the weight saved by no internal structure and placing it into the hull skins, they made a far better boat. The only issue is that they used an autoclave and it is a ridiculously expensive way of building a boat.

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The DNA’s have also all been built in an autoclave. A misnomer is that this process adds strength; it does to a very minor extent, primarily due to the heat curing cycle. Generally what the autoclave allows is the use of higher quality materials and longer processing times for more consistent products. Little of this changes how the structure is laid out or overall stiffness of the final platform.

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Sam

Bad wording - I was trying to say 2 things. First, using an autoclave is ridiculously expensive just to build boats, which is what Marstrom did. it needs a huge capital expenditure which is hard to justify in boatbuilding. Holland Composites, who build the DNA, have an autoclave for which they can utilise in other parts of their business making it viable to own one.      I was also suggesting that Marstrom's construction method overall was very costly.

 

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Regarding structural issues and technologic requirements for an A-Cat hull, 

I was  surprised to see foiling C-Cats with crossbeams bolted to the hulls, and stiff enought for 3 points sailing. Same remark for AC72 & AC50.

Should I conclude that is only the "fault" of the wing ?

Interesting thread, hope it will continue

Cheers

 

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Bonded beams has been standard on A's for 15 years?  At 2.3 meters beam, I suppose its easier to transport intact than a C class?

Bonded beams are stronger, lighter, and lower maintenance, than bolt on's.

Have heard it said that the mast of an A cat acts like an inverted dolphin striker, reducing platform twisting (wracking?), because of the twin forestays.  Not too sure on this, as the leeward shroud always goes slack.  

 

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Of course Max,

It was just to illustrate that a bigger boat with bigger loads than an A-Cat can stand these load without being build in one piece.

But of course, the quality (& price )of the carbon used for the C-Cat is probably very different from those used for A-Cat.

Interesting remark regarding the mast acting like a dolphin striker, not impossible, and it could make sense if you consider it as a kind of "pre-bending"  the plateform. It is just an assumption to  feed  the ongoing debate,  A-Cat specialists are obviously  in better position than me to provide the relevant explanations.

Cheers

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The trouble with using the mast as a king post is it needs to be able to rotate,  limiting the amount of tension you can put into the system. As a result, I haven’t bought the argument that it buys much platform stiffness. The 4 stay system limits side to side compression on the hulls so reduces the amount of material needed forward of the main beam.

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Sam is spot on. A's need top be able to rotate their masts which isn't compatible with rig tension. With the C's, they use a dolphin striker to counter the relatively high rig tensions they carry and this stops the platforms twisting. The wings have cut outs in their skins to allow for rotation, because they are relying on a mast spar that runs inside the shin and which everything hangs off. As people experiment with rudder differential and the like, we are applying increased loads so I do think platform twist is something the A's need to be considering, even if I don't have the answer for now.

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There are ways to get mast rotation with higher wire tensions. To date the weight penalty hasn’t made it worthwhile.

Structurally it would be nice to know the internal differences between the DNA and eXploder and Scheurer, along with thoughts on materials and designs moving forward. 

I also see the OP has dropped off, hope we didn’t scare him out of the class!

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