CAFAR - Canting Foil Arm System

Hello everyone,

I’d like to share a foiling concept we’ve been developing, currently under patent, which might open an interesting alternative design path for the Mini 6.50 class.

CAFAR – Canting Foil Arm System

The basic idea is fairly simple in principle: partially decouple hull form stability from righting moment generation by using a foil configuration that actively contributes to dynamic stability.

In a Mini 6.50 context, this could potentially allow:

• narrower hull geometries compared to today’s wide scow-based Minis
  
  
• reduced wetted surface in displacement mode
  
  
• improved light to medium wind performance
  
  
• additional dynamic righting moment from the foil system
  
  
• possible self-stabilizing behavior, depending on geometry
  

The concept works within the maximum beam allowed by class rules, developing an extended effective working span while staying inside dimensional limits.

We see the Mini 6.50 as an ideal high-performance test platform, but the underlying principle could also scale to:

• offshore racing yachts
  
  
• long-range performance cruisers
  
  
• large sailing yachts or megayachts looking for dynamic stability without extreme beam
  
  
• potentially even wind-assisted commercial vessels
  

We are currently entering a feasibility phase and would genuinely appreciate technical feedback from the community, especially regarding:

• trade-offs vs modern wide scow designs
  
  
• structural loads at the foil root in offshore conditions
  
  
• torsional and slamming load management
  
  
• ventilation and pitch control risks
  
  
• how realistic passive/self-balancing behavior would be offshore
  

We’re also open to collaborating with professionals interested in CFD/VPP analysis, structural modeling, foil optimization, prototype construction, or investment for a structured development program.

At this stage, critical and constructive input is very welcome.

Looking forward to your thoughts.

Francesco Belvisi

 

Hi fbelvisi, I applaud your inventiveness, and following through on an idea. My comments may be harsh, only to help you.
An elaborate flopper stopper. Can it bolt onto any/most monohulls? It will need fore and/or aft bracing for in any seas or minor collisions. It may need a running light to reduce night collisions. Would it withstand a trip to the Great Southern Ocean in a moderate storm or gale? What will happen if a large breaker dumps on it? Have you designed a hull to maximise strength where needed for your levers? On capsize how difficult will it be to right - will it have buoyancy? How will it behave when anchored in a fast flow tide or river?
Other questions may include: materials, weight, steering offset, etc.. It's interesting though.

 

Hello , thank you
The reasoning behind an object like this is that it should be built entirely in carbon fiber, with structural stays similar to a spinnaker pole arrangement, so that it works primarily in compression and minimizes bending loads.
The main drawback would concern the mast, which would need to be properly engineered and dimensioned to withstand the increased righting moment generated by the system.
A navigation light for nighttime use would be a good idea. However, it should be considered that when at rest the device would sit forward of the mast and could be fully retracted onboard during maneuvers.
I have designed it to be buoyant, with closed ends, but intended for installation on ballasted boats. My plan is to first test a prototype on a dinghy.

 

I think most of the claims are sales hype. For example, that it can be retrofitted on any boat without structural modifications. It doesn't explain how to change sides when tacking. It has a drag component that will make the boat bear down, which is likely to cause the boat to broach and capsize. In a storm, what do you do with the whole mechanism? The forces diagram is wrong. It shows weight up and also down. The righting forces are shown as added instead of subtracted. There are too many errors to take the design seriously.

 

Hello Gonzo,

thanks for taking the time to comment. Let me clarify a few points calmly.

Website and “sales hype”
The website is intentionally simple and was partly generated with AI just to present the concept quickly. It is not meant to be a technical dissertation.

The claims presented are those examined and accepted by the U.S. Patent Office. Anyone who has gone through the USPTO process knows that it is rigorous, demanding, and not particularly tolerant of hype or vague technical assertions. Claims are challenged, limited, and refined before approval.

The engineering substance sits behind the project — not in the presentation page.

Retrofit and structural modifications
The point is not that there are “no loads.”
The point is that the system avoids hull penetrations, foil trunks, and major structural openings — which are usually the most invasive and heavy part of adding side foils.

Of course any appendage generating load requires structural verification and, depending on the boat, reinforcement. That is standard naval architecture practice. It does not invalidate the concept.

Changing sides when tacking / gybing
The canting arm rotates around a longitudinal axis and the foil transfers to the new leeward side.

Yes, during certain maneuvers (for example easing the headsail or gybing) it may require slightly more coordination and possibly a few extra seconds. High-performance systems often involve this kind of trade-off.

The benefit is increased righting moment and reduced hull resistance. In offshore or distance sailing, that stability and sail-carrying power are worth far more than a marginally slower maneuver.

Drag, bearing away and broaching

Every lifting surface produces drag. The real question is balance and control.

Any yawing tendency caused by side force or drag is managed with rudder authority and trim — exactly as on modern foiling boats.

If drag alone automatically caused uncontrollable rounding down and broaching, then America’s Cup boats would simply sail in circles instead of racing at high speed. Clearly, force balance is a bit more nuanced than that.

The foil is positioned far from the centerline to generate a meaningful righting effect. Reduced hull resistance combined with increased righting leverage translates into more usable sail power. That is basic mechanics.

Force diagram

The diagram is intentionally simplified.

It does not show “weight acting upward.”
Weight acts downward.

The reason “weight” appears in two directions is to illustrate equilibrium — meaning that the upward support (buoyancy plus foil lift) equals the downward weight. The arrows represent balance, not two different weights acting in opposite directions.

It is a conceptual diagram to show moment arms and force balance, not a full vector-resolution drawing.

Storm conditions

The system is retractable and can be secured on deck. It is not intended to remain deployed in survival mode.

Experience and technical background

For context, I have designed and built boats that have sailed seriously and competitively without structural issues.

I have also collaborated with experienced professionals in the foil and high-performance racing field, and the concept has received thoughtful technical appreciation from them.

The feedback has been based on engineering reasoning and practical experience — not enthusiasm.

Constructive discussion is welcome. Practical evaluation matters more than assumptions.

 

That I believe.

So it is supposed to turn inside the backstay and above the crew's heads? The length on the diagram would not allow it to turn.

Not drag alone, but the force at the end of a long arm multiplies the torque.

There is clearly an upwards pointing arrow labeled "weight". There is no confusion on my part reading a forces diagram.

That is a really fantastic sales hype claim; "there are no loads". How do account for forces applied by the system producing "no loads"? This is just funny.

 

Rotation / rig interference
Have you looked at the actual geometry?
The arm passes forward of the mast — rather like a bowsprit or a spinnaker pole. Boats have been putting long structures forward of the rig for quite some time now without violating the laws of physics.

The drawing is schematic. It is not a class-rule measurement certificate.

Torque at the end of a long arm
Yes — force × distance = moment.
That is not a discovery; that is literally the reason the arm exists: to generate righting moment.
The structural strategy is to place the arm forward of the first main frame so that the resultant falls close to the neutral axis of the primary member, reducing torsional demand.
That is called load-path alignment, not “sales hype.”

Upward weight
There is, indeed, no such thing as weight acting upward on this planet.
The second arrow represents support reaction (buoyancy + lift) balancing gravity.
If two arrows disturb you more than bending moments, we may be debating graphic design rather than naval architecture.

“No loads”
Of course loads exist.
If lift is generated, reactions exist.
The statement concerns avoiding hull trunks and major structural cut-outs — i.e., changing the load path, not abolishing Newton.

And finally — the concept passed patent examination.
Patent offices do occasionally reject things that ignore basic mechanics.

If you believe a specific load case makes the system unworkable, I’d genuinely enjoy seeing the numbers

 

A technical discussion only works if there is a genuine attempt to understand the system first.
Otherwise it becomes time-consuming rather than constructive.

 

What frame on a composite boat? Further boat have a variety of structures. How do you propose a mounting systems, that as you claim, requires no structural changes?

In that case the arrow should be labeled "buoyancy". However, there is no positive buoyancy force on a foil. We are discussing proper diagrams, with correctly labeled forces, and forces that can exist and not simply added for advertising purposes.

So you admit the "no loads" statement is simply sales hype. Thanks

 

Gonzo,

you’re focusing on marginal details from a simplified public presentation and treating them as if they were the engineering basis of the project. That’s not serious technical critique — it’s nitpicking.

Nowhere did I ever state that there is “no load.”
If you can quote where I said that, please do. Otherwise, attributing that position to me is simply incorrect.

The website material was intentionally simplified to explain the concept to non-experts. Using that as proof that the system ignores basic mechanics (levers, flotation, etc.) is frankly a strawman argument.

And stressing that the forces on the foil must balance the boat’s weight is obviously a first-order simplification — a way to explain the primary load path in intuitive terms.

It is not a full dynamic equilibrium model, not a structural load envelope, and not a claim that the system operates in some static, single-force universe.

Anyone with a naval architecture background knows that the real picture includes dynamic amplification, righting moment coupling, pitch–heave interaction, wave-induced loads, inertia, transient peak factors, and offshore sea-state variability.

If every conceptual explanation had to include the full dynamic load matrix, no idea would ever leave a spreadsheet.

What I have been asking on my first post was:

• • trade-offs vs modern wide scow designs
    
    
  • structural loads at the foil root in offshore conditions
    
    
  • torsional and slamming load management
    
    
  • ventilation and pitch control risks
    
    
  • how realistic passive/self-balancing behavior would be offshore

If you believe the concept is structurally or dynamically unworkable, please identify the dominant limiting factor and under which assumptions (displacement, righting moment, foil area, speed range, sea state).

Attacking simplified diagrams instead of addressing real load cases does not move the discussion forward.

 

This shows the weight on the right going up. Then there are heeling forces going both right and left. The heeling arm and righting arm don't make much sense either.

 

That diagram is self-evident for any naval architect or engineer.
My initial comments in this thread were addressing much more specialized aspects of the system.

The sketch was introduced only as a visual aid to make the basic moment mechanism understandable also to non-specialists following the discussion.

In steady-state equilibrium:
ΣFy = 0 → Lift = Weight.
This simplification was assumed intentionally. The purpose was not to present a rigorous free-body diagram, but to illustrate the lever arms generating heeling and righting moments.

Heeling moment = aerodynamic force × vertical arm.
Righting moment = ballast weight × horizontal arm.

The vertical force balance is trivial in this context and was simplified for clarity.

Focusing on the arrow styling rather than on the moment equilibrium being discussed means concentrating on the finger instead of the moon.

 

This is not correct. The righting moment is the result of several forces. The ballast weight x horizontal arm would be one component when the boat has been knocked down. Otherwise, it depends on the angle of heel. The hull shape and weight is another component of the righting moment. Finally, you advertised foil would be a component too.

This is not a simplification, it is a totally wrong diagram. The forces vectors are indicated by arrows; the arrows must point in the correct direction.

If the finger points away from the moon, I would indicate it is pointing in the wrong direction.

By the way, I am an engineer.

 

Dear colleague,

I don’t believe this discussion will lead to any meaningful conclusion or provide something interesting and stimulating for the community. Moreover, it has moved away from the original purpose and scope of the thread.

For this reason, I think it would be best to stop here.

Best regards,

 

Francesco I would suggest replacing the word "weight" with "force" on your diagram to eliminate possible ambiguity.

I have noticed that this otherwise excellent site suffers quite a lot from egotistical points scoring. Not the sort of behaviour I would expect from mariners where team work is essential to survival.