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"AC25" Foiling Catamaran Project


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Coming up on the summer, I am thinking about starting a new boat-building project, the "AC25". The idea is to essentially build a 25-foot, double/triplehanded half-scale version of the AC50/F50. I hope that the finished product will be similar to the ETF26 foiling catamaran, as seen below.

EasfyToFlye26June2020.jpg?resize=1000%2C635&ssl=1

For the construction process, I will soon begin on the construction of the two hulls. I plan on building them from high-grade carbon fiber, using the method John Lindahl used on his LR6 A-class build.

https://lindahlcompositedesign.weebly.com/lr-6.html

The AC25 will not be using wand-controlled foils in the vein of the S9 or Formula Whisper, but a pair of deployable and retractable foils. I am modelling the design in Fusion CAD currently, and the design is very much inspired by the foils used by the SailGP boat. They will extend past both hulls, thus providing more righting moment

F50s upgrades preview over AC50s - Catamaran Racing , News & Design

Fellow Sailing Anarchists: any advice or thoughts about this admittedly ambitious project are welcome.

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34 minutes ago, eastern motors said:

Very cool and very ambitious.  Do you have other people involved?  What's your experience and budget?

I have a few friends of mine involved. I have experience building canoes and other simple watercraft, and budget wise I'd like to keep the AC25 under the 40k or so for spending.

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I'd offer some unsolicited advice because you have a budget:

- don't use high modulus carbon everywhere (I assume that's what you mean by "high-grade"). It's best reserved for things that have to be extra stiff like beams/mast/foils/rudder and reinforcing for same i.e. internal bulkheads or ring frames at the beam connections of where foils enter the boat. For such a small boat I'm not sure why you need the added stiffness for the hulls

- do vacuum bag unlike John Lindahl. It adds little cost, is easy to learn if you haven't done it, and ensures really good bonds of the foam to the skins. At the end of the project sell off the vacuum pump if you don't need it.

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55 minutes ago, Zonker said:

I'd offer some unsolicited advice because you have a budget:

- don't use high modulus carbon everywhere (I assume that's what you mean by "high-grade"). It's best reserved for things that have to be extra stiff like beams/mast/foils/rudder and reinforcing for same i.e. internal bulkheads or ring frames at the beam connections of where foils enter the boat. For such a small boat I'm not sure why you need the added stiffness for the hulls

- do vacuum bag unlike John Lindahl. It adds little cost, is easy to learn if you haven't done it, and ensures really good bonds of the foam to the skins. At the end of the project sell off the vacuum pump if you don't need it.

Right - high modulus will be reserved for the foils and bulkheads then. I will definitely look into the vacuum bag as well. As far as the mast goes - would there be a pre-existing race rig suitable for a 25foot racing catamaran, or should I look into mastmaking and rig building?

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Why not build an A cat first?  At least you can get the foils and spars off the shelf, for a first stab at a high performance boat?  The hydrofoils are an adventurous project for a home build, they don't have to be far off to be useless, whereas you can buy old generation A class Z foils by the kilo.

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21 hours ago, 920HYBRID said:

The AC25 will not be using wand-controlled foils in the vein of the S9 or Formula Whisper, but a pair of deployable and retractable foils. I am modelling the design in Fusion CAD currently, and the design is very much inspired by the foils used by the SailGP boat. They will extend past both hulls, thus providing more righting moment

Without the wands, or an expert crewmember actively controlling the foils, how will you keep the boat from crashing? The foils you've sketched won't be self-correcting, and "deployable & retractable" isn't enough. 

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1 hour ago, Doug Halsey said:

Without the wands, or an expert crewmember actively controlling the foils, how will you keep the boat from crashing? The foils you've sketched won't be self-correcting, and "deployable & retractable" isn't enough. 

Doug is right. This is an important point.

For a more practical approach, get your hands on a Flying Phantom or a Nacra 20 FCS. Their foils are sorted -- and that's no small feat. You can explore "scaling up" either of those boats.

 

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4 hours ago, Doug Halsey said:

Without the wands, or an expert crewmember actively controlling the foils, how will you keep the boat from crashing? The foils you've sketched won't be self-correcting, and "deployable & retractable" isn't enough. 

The boat will be double or triple-handed with a crew member actively flying the boat. Although - if you all think it is far too complex a system to feasibly build myself, I am open to using GC32-style J-foils. If I recall correctly, however, the 26-foot "Easy to Fly" catamaran uses dedicated foil/flight control, and is fly/sailable by relative amateurs even. And as far as building an A-cat goes, I already own a DNA F1X, hence why this project is of more interest to me. Budget-wise, I am flexible and willing to spend much more than the baseline 40k.

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Given that you already have a DNA, I think you probably have a good appreciation for the technical quality required for foiling.  It is not something that can generally be done well by a home builder.  After going through quite a few generations of foiling boats in the A-Class myself, I have seen first hand how much development and iteration is required to make something foil well and quickly. 

I recommend off the shelf tech as much as possible and ideally things that are well refined like your F1X which came about after seven years or so of fairly constant foiling development.  Or work with naval architects, commission or conduct extensive CFD work, and likely be prepared to still have to purchase more than one set of molds, several foils, and correct structural issues at substantial cost and time.  I think that is roughly what every foiling class has experienced thus far.  

All that said, why not get the ETF 26 you mention, assuming they are well sorted now at maybe $200K if they are available?  You could then focus on the foils or rig for additional development if you wanted and maybe use it as a test bed to make something bespoke in the future with AC / SailGP levels of mechatronics.

The other option that comes to mind is the TF10 of which there are now a few used ones for sale but that is a larger boat.  https://dnaperformancesailing.com/our-boats/used-boats-for-sale/.

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5 hours ago, Lost in Translation said:

Given that you already have a DNA, I think you probably have a good appreciation for the technical quality required for foiling.  It is not something that can generally be done well by a home builder.  After going through quite a few generations of foiling boats in the A-Class myself, I have seen first hand how much development and iteration is required to make something foil well and quickly. 

I recommend off the shelf tech as much as possible and ideally things that are well refined like your F1X which came about after seven years or so of fairly constant foiling development.  Or work with naval architects, commission or conduct extensive CFD work, and likely be prepared to still have to purchase more than one set of molds, several foils, and correct structural issues at substantial cost and time.  I think that is roughly what every foiling class has experienced thus far.  

All that said, why not get the ETF 26 you mention, assuming they are well sorted now at maybe $200K if they are available?  You could then focus on the foils or rig for additional development if you wanted and maybe use it as a test bed to make something bespoke in the future with AC / SailGP levels of mechatronics.

The other option that comes to mind is the TF10 of which there are now a few used ones for sale but that is a larger boat.  https://dnaperformancesailing.com/our-boats/used-boats-for-sale/.

I'd be more than willing to source off-the-shelf masts, rigging, and even foils for the project. I am very much hoping the AC25 to be a test-bed for custom foil development in the future too. From where could I source such components?

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Check out ARC, Roberts Catamarans, Supercat for used or new masts and rigging. They have been making boats in your size range with carbon masts for decades (22 x 12 with 38.5 ' mast, 27 x 16 with 41' mast, and 30 x 16 with 45' mast). The 22 is designed for 2 crew, the 27 and 30 designed for 3-4. You might be able to find something that fits your needs.

Cool project, good luck.

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Foiling brings a different level of loads, so some find that repurposing older gear works for a bit sub-optimally and then breaks.  The speeds are higher and the decelerations greater.  Traditional platform stiffness, something that wasn't that big a deal for the nicely made Supercats in 2 dimensional sailing, won't work as well when the windward rudder is now set to apply righting moment and the boat pitchpoles or even just ventilates and falls off the foils at speeds higher than it ever encountered in the past.  Relatively tall bows with V'd underwater sections will cause drag and increase steering loads in touchdowns.   Boats that migrate to foiling can have transoms overloaded, board cases / bearings crack or dislodge, beam issues, sails too full which causes heave instability, etc.  Desirable apparent wind angles go from maybe a 70 degree range on either side in displacement mode between jib to assym kite to probably 20 degrees or less as the foiler always goes upwind when foiling.  The boom, mainsail controls, etc also need to be changed to lower the center of effort and deal with increasing sheet tension.  Board and rudder design, build, weight, load, and finish requirements go up dramatically.

A-Class masts have gone up 1.5 kgs for example in making the transition from traditional sailing to foiling. Ask Matthew Smyth on a small scale about conversions as he has converted his classic A2 to foiling and been through most all of these issues and required adaptations with a great spirit and attitude and with generosity from other class members who contributed equipment upgrades. I chuckle as I think about it, but even Matthew's trampoline did not make it through the conversion as he needed a deck sealing system.  In the end, I think the forestay tangs and maybe the mast rotation system are about all that persisted from his original equipment list.  Maybe I am wrong, but it is a bit stunning how much should be changed to have a good foiler.  

I have no firsthand knowledge of the ETF26 but the primary suppliers look to be noted here: https://www.yachtingworld.com/extraordinary-boats/etf26-trailer-foiler-foiling-124381.  

I don't mean to discourage the endeavor as it is awesome.  You may have all this info already but wanted to share in case it is helpful to others as the effort is big regardless of the route.

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3 hours ago, EZE said:

Check out ARC, Roberts Catamarans, Supercat for used or new masts and rigging. They have been making boats in your size range with carbon masts for decades (22 x 12 with 38.5 ' mast, 27 x 16 with 41' mast, and 30 x 16 with 45' mast). The 22 is designed for 2 crew, the 27 and 30 designed for 3-4. You might be able to find something that fits your needs.

Cool project, good luck.

and the carbon (filament wound) mast for my supercat 17, a 28 foot spar, was just under 10k. that is a big bite out of a 40k base budget.

 

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3 hours ago, Lost in Translation said:

Foiling brings a different level of loads, so some find that repurposing older gear works for a bit sub-optimally and then breaks.  The speeds are higher and the decelerations greater.  Traditional platform stiffness, something that wasn't that big a deal for the nicely made Supercats in 2 dimensional sailing, won't work as well when the windward rudder is now set to apply righting moment and the boat pitchpoles or even just ventilates and falls off the foils at speeds higher than it ever encountered in the past.  Relatively tall bows with V'd underwater sections will cause drag and increase steering loads in touchdowns.   Boats that migrate to foiling can have transoms overloaded, board cases / bearings crack or dislodge, beam issues, sails too full which causes heave instability, etc.  Desirable apparent wind angles go from maybe a 70 degree range on either side in displacement mode between jib to assym kite to probably 20 degrees or less as the foiler always goes upwind when foiling.  The boom, mainsail controls, etc also need to be changed to lower the center of effort and deal with increasing sheet tension.  Board and rudder design, build, weight, load, and finish requirements go up dramatically.

A-Class masts have gone up 1.5 kgs for example in making the transition from traditional sailing to foiling. Ask Matthew Smyth on a small scale about conversions as he has converted his classic A2 to foiling and been through most all of these issues and required adaptations with a great spirit and attitude and with generosity from other class members who contributed equipment upgrades. I chuckle as I think about it, but even Matthew's trampoline did not make it through the conversion as he needed a deck sealing system.  In the end, I think the forestay tangs and maybe the mast rotation system are about all that persisted from his original equipment list.  Maybe I am wrong, but it is a bit stunning how much should be changed to have a good foiler.  

I have no firsthand knowledge of the ETF26 but the primary suppliers look to be noted here: https://www.yachtingworld.com/extraordinary-boats/etf26-trailer-foiler-foiling-124381.  

I don't mean to discourage the endeavor as it is awesome.  You may have all this info already but wanted to share in case it is helpful to others as the effort is big regardless of the route.

Thanks to all for the insight. I am fully aware of how difficult and frankly over-ambitious this endeavor is, but I'd still like to give it a shot. I will build the platform to be overly stiff and strong initially, as foiling does put an entirely new set of loads upon a boat. The hulls, given that their shape will be copied from the AC50s, should have no issues with touchdowns and such. Foils wise, I will commission plug-making to a third party, and attempt to build them strong enough myself, but I am open to a full custom commission. As far as the rig goes, however, I will look into the Supercat/Roberts/ARC route, and go from there.

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So I am currently working out the foil designs for the AC25. If I am understanding it correctly, L-shaped boards as seen on the AC50 and F50 catamarans require a flight controller to consistently adjust rake, cant, and angle of attack, as they are not self-adjusting. If I am to use such L-shaped foils on my AC25, I would need to build a mechanism for adjustment of rake, cant, and AoA. However, J-shaped boards like those on the GC32 are self-adjusting, as if they ride too high out of the water they lose lift, and if they ride to deep they lift themselves out. Which system would be preferable for my project?

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There is a 25’ development class catamaran. It is called the C Class and it is where the almost all the fundamental technology of the AC catamarans was developed.  There are existing platforms and wings that would be fine starting places for your project.  At the very least you should consider it.

SHC

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19 hours ago, Steve Clark said:

There is a 25’ development class catamaran. It is called the C Class and it is where the almost all the fundamental technology of the AC catamarans was developed.  There are existing platforms and wings that would be fine starting places for your project.  At the very least you should consider it.

SHC

I know about and love the C-Class catamarans, but given their limited worldwide reach and the small numbers of the class, I have been as of yet unable to find any platforms or boats available for purchase. I am certainly considering it, though.

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The Canadian ETS project has stopped. The second platform was credible, their wing was a POS, but it exists.  I have no idea what they are going to do with is or how much they want.

 Alpha, the Sentient Blue boat, is for sale in Europe.  It is one of the best conventional ( pre foiling) boats.  The wing is very good.  John Downey who post here as Desert Wings had hel listed in the classifieds. This is the boat that beat Cogito in 2007.  

I have 3 platforms ( Cogito, Aethon, & Orion), one modern wing and the Patient Lady V wing, and the spar and control system of the 105 wing.  All of which you could talk me out of for money and the effort to convince me that you are real.

SHC

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2 hours ago, Steve Clark said:

The Canadian ETS project has stopped. The second platform was credible, their wing was a POS, but it exists.  I have no idea what they are going to do with is or how much they want.

 Alpha, the Sentient Blue boat, is for sale in Europe.  It is one of the best conventional ( pre foiling) boats.  The wing is very good.  John Downey who post here as Desert Wings had hel listed in the classifieds. This is the boat that beat Cogito in 2007.  

I have 3 platforms ( Cogito, Aethon, & Orion), one modern wing and the Patient Lady V wing, and the spar and control system of the 105 wing.  All of which you could talk me out of for money and the effort to convince me that you are real.

SHC

@920HYBRID this is with out a doubt the best offer and smartest way for you to go.

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920hybrid, can you explain your goals? So we can understand the project. You want to build a one off just to sail? To race? Or are you planning on selling boats? Maximum performance? To beat who? Or you would be happy to just make it fly even if it's not the fastest foiler? Thanks and good luck!

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On 5/31/2021 at 3:21 PM, Steve Clark said:

The Canadian ETS project has stopped. The second platform was credible, their wing was a POS, but it exists.  I have no idea what they are going to do with is or how much they want.

For reference - https://www.adhesivesmag.com/articles/96458-setting-sail-with-structural-adhesives -- these guys were in Miami Foiling Week 2018 and sailed their C Class there. 

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i have day dreamed about similar topics.  The M20 vampire project looked interesting.  The outboard, swingdown type foils seem like a good solution.  Wands seem like they would be good to minimize crashes.  An autoclave for the mast beams, and foils would be nice. Also, if there are wands then the foils will not need so many compound curves.  Building those foils strong enough with the perfect curves is a pretty big technical achievement on it's own...$40,000 has no doubt been spent on just that alone on other projects.

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