Indeed, there is no “truth” to be found, I miswrote.
But there are certainly ideas that are healthy to challenge, even if it can get a bit overwhelming and deteriorate the good vibes due to the “debate” format they take.
Happy to see what I shared being challenged in return, I don’t claim to have the truth, that’s why I mostly post pictures/measurements/reports.
Nice,
One thing I think is very interesting that you posted (among others), is the fuse diameter. This has often come up as point of differentiation, where lower cross section supposedly results in less drag. I think this speaks to the same physics around wetted area being more important than thickness for the mast. Is there anything quantified on this?
@Dontsink my AFS stuff is all 2 bolt M8 which has done well but the Mikes Lab, F-One, and maybe Duotone all go M6 if I am correct? That’s why they 100% need 3 bolts. However, I think the new KT foils are 3 bolt M8 which I think Kane said was to “future proof” the foils.
In my climbing days we taught the value of redundancy and I think the instructor who originally taught me cited a NASA paper about it. The 2nd bolt is a huge upgrade in security over 1. The 3rd bolt is also a significant upgrade, but not as big of an upgrade. A 4th layer of redundancy is a relatively insignificant improvement in security.
I think that in the fuse situation there is a combination of thickness and wetted area happening, it can’t be one without the other right? I think wetted area of fuse is best impacted with fuse length.
For masts, I think the thickness vs wetted area thing is honestly a bit jumbled up and misleading at the moment. They both matter and they both impact the riders experience differently. IMO picking the trait that you want to alter in your ride is what’s most important and knowing if thickness or wetted area is going to enhance that trait is what needs to be decided for the individual rider.
I’m not sure everybody agrees with what you think everyone knows 
.
Also, not all “U” connections have parallel sides. Wear on parallel sides will cause a loose connection with some bending on the bolts.
Unifoil (and Lift thanks @Eriefoiler ) iss tapered - “V” connection? So the little bit of surface wear that “everyone” is freaking about can only cause the mast to seat deaper into the fuse.
Both type of connections rely on the surfaces to be clear of sand/salt to ensure consistent AoA.
Bolts are designed for tensile loads. Any connection that creates shear or bending loads on a bolt is a bad design.
Will also be interesting to see dimentional longevity of the AFS style connection - same force over a much smaller area creating much higher compression force and possibly turning sandy interfaces into a grinding paste.
Time will tell.
I was wondering if this move towards M8 could be trouble, with mast sections already as thin as 13mm near the fuse it gives 2.5mm (or less if front or back bolt) on each side of the bolt .
And in those 2.5mm you have to accomodate metal insert+carbon…pretty tight.
A full metal lower section as that Chubanga someone posted maybe a better way.
FWIW the Lift mast foot is definitely not parallel:
It measures 20.47mm at the base and 17.15mm at the tip.
Design will be critical for sure and that might lend itself to the butt joints because it gives more flexibility to the mast shape and fuse size than the mortise and tenon joints.
Here you can see the meat of the AFS mast actually blends into the overall shape of the fuse allowing it to be 26.4mm at bolt insertion.
But then it dramatically tapers down to 12.7mm within 3 inches of touching the fuse.
I wonder if this shape/design will actually be a necessity to achieve the thinnest mast profiles in the future?
Thanks for the correction. I updated my comment. Lift then definately more bulky on the mast foot. Would be interesting to know if their fuselage sides are proportional.
Of couse the carbon layup around the box would also be critical. No way we can know that.
I would personally take anything said at a trade show with a grain of salt. By the time we’re at a tradeshow, the job is to sell gear - which means make up a believable story about why what we’ve done is the best.
Structural design work isn’t always intuitive and can’t be boiled down into something easy to understand by a 5yr old. The answer is always - it depends. There is nothing fundamental about a socket or face style connection that must be stiffer or less stiff. Shortcomings of either can be overcome by other choices such as materials and cross sections. What I was trying to point out is that from a structural standpoint, the face style connection is easier to execute into a stiff joint. Done wrong, it won’t be. Done right, the socket style can be just as good. But always there are tradeoffs and the best is to start with the fundamentally best joint.
The front wing socket also appears to be tapered. The issue that causes wobbling is most likely when the foot bottoms out in the socket - which lift comes very close to doing. Simply adding some epoxy or tape on the mast foot is a easy fix to this. I disassemble my foil frequently and have not had issues.
Agree. Or a light spray of clear epoxy paint over the mast foot. Not needed for the last few years riding and swapping fuses a few times a week.
I suspect the wear is mostly on the 2K coat most manufacturers put on. If youve ever tried sanding clean carbon, even with 80grit, it takes massive effort to even make a few microns “damage”.
So many variables, but i suspect a lot of the damaged reputations happen in the spray booth. A joint comes out of a mold to spec and the cowboy with a spray gun screws up the connection by adding a paint layer
All styles have their own perks and drawbacks. It is up to the designer to balance the features in a way they think is optimal.
The advantages to the socket are connection strength and strength of the thread inserts. It is really nice not having to rely on bolts for your strength/stiffness; barrel nuts make construction and repair simple and reliable.
The ability to use m6 bolts reduces drag from the head of the bolts and allows rounder bottom of the fuselage.
Hiding the inserts inside the connection also allows for a thinner mast and lower drag blend to the fuselage.
The disadvantages of a socket start with the fuselage. Removing so much material weakens the fuselage, resulting in larger diameters especially when using carbon. The connection is only as strong as the wall holding it.
The second set of flaws has to do with wear, seating, and stiffness over time. The socket needs super tight tolerances not to wobble. Most versions use a taper to fix this which works in roll but the lack of contact on the bottom surface combined with low taper angles leads to the connection settling as you ride it, leading to inaccurate pitch angles between the mast and fuselage. Steeper taper improves this but also removes even more material fr the fuselage. If you have ever come in with a loose front bolt this is the connection settling.
From my experience axis actually has a pretty good implementation of a socket design. The straight walls mean no settling. They have the tolerances really tight. After a year or so of hard riding you can just re pot the connection with epoxy and it is better than new.
For race specific foils using metal fuselages, the foot may be the lowest drag as it minimizes seam area on the fuselage. You can go pretty small with the slot if accommodating to thicker masts or requiring extreme strength is out of the picture. Look at Levitaz R series for a great example of this.
Now on to the foot style:
Foot style connections sacrifice ease of manufacturing and ultimate strength for a fit that is more consistent, stiffer over time, and smaller possible fuselage diameter.
A foot style connection is easier to assemble and disassemble. Most slot connections only work when everything is extremely tight. In my experience, if you don’t need a mallet to put it together or take it apart a slot connection is not working optimally and will flex. In contrast, the foot is only as tight as the bolts and way simpler to use.
The problem with most foot connections on the market is they are just under engineered. Connections with a small width or using m6 like f-one, Ensis, or mikes lab will not stand the loads of modern large high aspect wings and large boards. Afs and especially duotone are much stronger. When looking for a foil using a foot style connection, I would set an absolute minimum width of 20mm and 2x m8 bolts. For anyone pushing hard, I would want closer to 30mm and at least 2 m8. I recommend using 316 stainless or better bolts.
A well designed foot connection will wear in. High spots will experience more pressure and wear down, spreading the wear to match the load. They can wear asymmetrically but this can also be fixed with a sanding block.
Foot style connections are easier to make with carbon. They have no thin walls, fewer sharp corners, and more robust cross sections.
I am also a fan of hybrid foot/slot connections like phantom uses. These still require strong bolts for stiffness but don’t rely on the bolts for maximum strength. Inserts can also be done with a barrel nut like the slot connection allowing a thin mast all the way to the fuselage.
The disadvantage of this design is it will need a larger fuselage compared to the foot only and it may be harder lay the fibers in the mold.
The last popular style is zero mast to fuse connection. Gofoil and Flite use this option. This can increase the size of the mast piece and make traveling difficult, or the designer can move the connections close to the mast, increasing the force on the connection. It also makes the mast more expensive and loses the option of a one-piece wing + fuselage and the ability to change fuselage diameter to suit foil purpose. I think there is potential for something cool with some more experimentation.
A few brands are more unique like Armstrong and gong but these would require their own individual breakdown.
In summary foils are a structural nightmare and we are not by any means close to a perfect system. Buy something strong or something with a great warrantee 
Fantastic. Thank you.
That might be the best comment I’ve seen on this forum. You can really tell who here works in the industry vs the others.
I’m not familiar with phantom, but I wonder if cedrus could be added to the hybrid connection column. Bolts for initial load, with backup(might be a better word for it) provided by the m10 pins at fuse and collar up at the plate. That plate is like a socket/butt joint hybrid. As for those pins, I’m not a machinist but I find it incredible that a random adapter slides into those holes in the mast with that tolerance. SEEMS like it would be hard to manufacture but I’m probably wrong.
Can you give us the explanation of the difference between monobloc front wing versus the kinds of connection systems found in afs and kt? It seems like the monobloc had an advantage in less drag the same way that a thinner fuselage has
Would love to hear your thoughts on the new Slingshot system.
So, just for sake of argument (thanks @KDW for talking some sense into this thread!) are we at a stage where we could have a “standard” emerge, with this mast/fuse joint as the interface? Assessment on the options below. I would say probably not, but fwiw:
Based on this it seems likely not an obvious “standard” with the uncertainty
I love the zero mast to fuse connection, but it seems the compromise is that you have to go into an Armstrong / takuma connection system for the front wing. Personally I think thats one of the worst front wing connection systems along with axis, so the trade off more than offsets the benefit of the zero mast to fuse.
I think the best system in terms of design is the delta M frame. No connection on the mast to front fuse - rear fuse detaches for logistics, simple front wing connection.
If only there was a top of the line surf wing for it!
