Any experience with high load jumping using a "kite foil box"

[Horst Sergio]

I actualy design plans for a new board to give them to my shaper.

To be as flexible as possible I want to set inbetween the two standard rails for plate mount also a rail that will allow at least three position for kitefoilbox (kfb) strut heads (-4 cm, 0 cm + 4cm) .

I know this will go on cost of weight, but I like the kfb concept for shorter struts without big strut heads for traveling. And I don't have doupts that a three positon kfb will be weaker than a one place if adding a reinforcment frame inside the board in the middle of this elongated box to prevent it from getting stretched towards the sidewalls. The small front walls shouldn't take relevant load anyway.


But as I restarted boosting a bit, which could also be a goal with a maximum strut length of 90 cm and kfb (longer just with platte), I wonder if even two screws of normaly just M6 in a distance of 8 cm and the small box in general is able to take high loads. When I see what damages allready happen to plattes with 4 x M8 screws at a distance of 16,5 cm …. you know what I mean

As also not too many brands using kfb and most of them use it just with freeriding strapless style foils….

So anybody around, who has jumped his kfb setup, in the best case with a volume board, for a year without any problem and maybe a video of your riding style and your weight to evaluate how hard the load is.

Thanks a lot.

[cglazier]

The KF Box and the Tuttle box and the Pro Box all are designed to take most of the forces on the sides and front/back edges of the box. The screws used to hold them in place shouldn't normally see much load. In fact Alpine used only one screw, (although now they have gone to two screws).

The plate system is different and the four screws all take significant loads. As long as the mast is tightly installed I would expect something else would break before the screws would break in any of these systems.

But if the mast is loose and moving around then sheer forces and metal fatigue can certainly cause a screw to fail.

(A typical M6 stainless screw has a tensile strength of 9KN or roughly 1000 Kg of force... and an M8 stainless screw is almost twice that)

CG

[Horst Sergio]

Hi cglazier,

yes I see your points, but I am sure it is not about absolute values of the strengt of a best material M6 screw but much about load caused by leverage. I have seen constructions with M6 screws of best quality steel that broke during riding and looked like out of a tensile test. Studied a bit material science so a bit know what I am talking about. And it is not only about screws but more about if k-f box in creates too high loads due to its small size to all components, especially to a box inside a volume board.

Till now my 3 most used boards have never lived much longer than 1 year. Two of them started to get soft on the plate-strut conection as most of them can't resist to the pull out forces they see on the front screws when the nose touches down at high speed being kicked back upwards, while the foil still wants to dive deeper. ...

And till now I have seen no video of someone with a k-f box boosting hard for a year or more.
What are all those f-one foil owners do, staying on the ground?

Anybody arround?

[cwood]

Some of our most frequent boosters ( 10's of thousands of massive boosts) are running on Alpine with KF. Haven't see one fail yet which amazes me. Other brands were not as robust. Personally I prefer the strength of the distributed load of the Moses plate system. Hard to imagine the single boxes holding up but they seem to on the Alpines at least. I do think the boards are quite heavy so they may be well reinforced and braced between stringers and such.

[Peter_Frank]

KFBox or Tuttle box or whatever box are cleaner and more sleek and in every way also really strong when mounted correctly, using a good female box.

But they can of course also be junk, if the box is'nt mounted right

I like a box simply because they are "clean", eventhough they are not needed for my somewhat clumsier style

Because, having a beautiful clean board, and then slamming a plate with maybe screws or bolts sticking out, and a bulky edge/plate down in the waterstream before foiling, simply seems so wrong in my eyes eventhough I know it doesnt matter that much and they can be made a bit cleaner somtimes - but it is just wrong for me mentally

I've had the KFBox in different depths, mounted on a handful of kitefoilboards, and also on my windfoil (where the loads are much stronger usually).


As said in an older post, simply loving this distribution of forces which is an engineering masterpiece IMO, utilized to the extreme here with a sleek long carbon box so even the thinnest board will get stronger and a lot stiffer:





Less can also do it, and it you got a thin board, this box can be used for boards 20 mm thick only, and you can choose yourself if you want 1 or 2 or even 3 screws, depending on your mast: https://www.ketos-foil.com/en/foil-kf-b ... iddle.html

Again, nothing is stronger than the build/inserts used.

Can not contribute to your question Horst, about whether some has used this box for "endless" jumping - but IMO it is not about the box really, but more about the build itself whether it will hold up or not

PF

[BWD]

I would think you would want m8 screws, and to be sure the top part of the mast was a true monolithic carbon fiber laminate all the way through, since so much more load would be put on the screws and thence into the inside of the mast, without any front or rear walls to the box.
It would also be a big advantage to have not a normal kf box mast head but instead a longer one.

[Breze]

First post,longtime reader and almost same considerations
Today i got the message from the french alps, jumping is ok with the "KF box out"
https://www.ketos-foil.com/en/foil-kf-b ... x-out.html
My diy board has strong rails and hopefully sufficient reinforcements but with 2.5 cm not enough meat
to install the KF box in.
With a "third rail" or slot in between the rails, it would be possible to unscrew the mast and
still use the rails.