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Lightwind kiteboard build, planing ahead

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phuqit
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Lightwind kiteboard build, planing ahead

Postby phuqit » Tue Jun 26, 2018 9:40 pm

Hey guys, I am seeking for advice.

I would like to build a light wind kiteboard, from the tests I've done so far, I'd probably go ahead with Flydoor 5 XL as a template (170x50): flysurfer.com/project/flydoor5/. The goal is to have a comfy board for those light wind conditions, to accompany me on my 12m and 21m Flysurfer soul kites. I also have the Flysplit 2 (139x43), but it sometimes feels a bit too flexy for my taste (I'm 100kg, intermediate skill level type of rider - freeriding, jumping, some hooked tricks). The goals are to keep the board as light as possible, and reasonably thin, without flexing wildly.

My current plan is to:
1) use a western red cedar strips for core material (I can get it much easier than Paulownia strips, and by the looks of it, it's comparable stats-wise), material cost being ~50€. I then plan to CNC it, keeping it thicker at the center/foot pads area, and to thin the rail and tip portions to something like 3-4mm, to get more flex at the ends.
2) I plan to use moderate rocker, something like 30-40mm at the tips, that should allow it to perform better in chop. Slight single concave, as well, ~1cm at the center, too - not sure what's best - suggestions welcome. Plan to use 5mm plexiglass as the rocker table.
3) Use 250g unidirectional carbon in the center/pad area both top/bottom, to ensure it doesn't flex too much.
4) Use 300g biax carbon on the tips (which are ~3mm thick).
5) PU rails, fin reinforcement, and flanged stainless steel nuts for pads/handle.
6) I'd like to cast the nobile's click'n'go fin attachment mechanism from PU, it's super easy and convenient to use http://nobilekiteboarding.com/products/ ... -gf33.html. Got some molding materials at hand, will give it a try with PU and resin+fiberglass.

I'd like to do the job as resin infusion, because I have all the equipment and materials, and supposedly it keeps resin usage at the minimum.

So the questions are:
1. Should I leave the center core part ~1cm thick, and apply uniform layer of carbon, or make it thinner, around 6mm, and double the carbon layer to compensate? I'm leaning for the latter, since it supposedly gives me a more resilient board with similar flex characteristics?
2. Should I apply another layer of FG on top/bottom, just to protect the carbon layer from the elements? Right now I plan to use a few thin layers of UV stabilised epoxy to get that piano finish.
3. Provided I do the resin infusion, what would be the proper way to ensure that the resin passes from top to bottom? I assume keeping the core strips glued with some spacing between them might help with that? But that would probably make it somewhat weaker structurally...
4. Painting a logo or something on the top sandwich layer, before infusing... what paint to use? I'd simply print the template on paper and cut it manually, or perhaps use a plotter.

Any advise would be much appreciated.
pq

BWD
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Re: Lightwind kiteboard build, planing ahead

Postby BWD » Wed Jun 27, 2018 4:09 am

For your weight make it 15-20mm thick instead.
0-90 300gsm cf over all top and bottom.
Plus 45/45 300gsm Between outer foot strap screws through center.
If you want more flex use glass instead and maybe an extra layer on the top.
Skip the PU rails unless you want it to weigh an extra pound or two. Or figure out how to make them very narrow.
Instead of pu you can just wrap an extra layer or two of glass or carbon over the rails.
Infusion if you haven’t done it before will require several small test projects before doing a whole board. Or a gamble. Even then you have to be very confident to go for a one shot infusion of the top and bottom. Usually confident means experienced.
For what it’s worth, failure mode in kite boards is skin buckling on the compression side, meaning thinning your lamination by infusion will give lighter tighter lams but not more strength vs buckling. In other words not always worth the trouble for a few grams saved.
Boards always break right outside the footstrap area so continue your 2nd lamination layer(s) a few cm past this. Also better if it doesn’t run straight across.
Cedar will be heavier than paulownia but I’ve used it.
Good luck and have fun

fluidity
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Re: Lightwind kiteboard build, planing ahead

Postby fluidity » Wed Jun 27, 2018 10:27 am

170 x 50 will be massive for your weight. My last board I ride most, is 130 x 40 with high concave and about 18mm rocker. I'm currently between 99 and 101 kg so very similar weight. I like to fly overpowered to jump higher. My previous design was quite similar to an Ocean Rodeo Mako though I used my own 3D process to create the contours. That was low rocker, 150 x 45. I think you will find that to be a sweet spot for your a 12m and 21m kites. It's verging on too big a board for a 12m kite but is still controllable down to a 7m kite, but gets me upwind at a higher angle than most kiters. On the 21m it will also be fine I'm sure, and definitely more manouverable than a 170 x 50 board which is close to tandem kiting size. For most of my kiting I really prefer my 130 x 40 board which is so much softer landing and the concave doesn't fight to bend my toes down if I slide it sideways.

But then my local conditions would favour an average of 10m kite for my weight for most of the year....

If you want a look at a couple of my builds they are here:
viewtopic.php?f=107&t=2398790
The Paulownia wood with Kwilla rails has worked great so far.

I'm setting up for infusion too but like BWD says above, there is a lot that can go wrong.
Agree with some of his comments about location of materials too.
From my point of view,
Carbon is supposed to be a lot harder to infuse than glass due to much thinner fibres. On top your main loadings landing a jump are compressive, this is where carbon fibre excels. Maybe a 100mm wide carbon tape strip going 150mm past foot strap pads. zigzag the ends to increase potential shear line length and difficulty.
Glass over it.
For underneath, use glass/innegra. More stretchy which is what you need.
For your rocker, Plummet on here has suggested using the trick that one of the manufacturers has, of a rocker that straightens under loading. So close to constant thickness along the length. More thickness gives more buoyancy for board recovery, I've found around 8-10mm thick still has good ability to bend. Too thin and you'll have to trim your T-nut inserts and starting the footstrap bolts will be harder and with less engagement of threads.
Adding layers of epoxy afterwards: I've been working on a twintip hull mould the last 3 weeks. I'm finding it's really hard to get the epoxy adhering uniformly on multiple layers. Polyurethanes aren't as tough but gloss flat easier due and have more UV protection.

Getting your plexiglass to follow a concave will be a mission. I've experimented with vacuum moulding PETG RC Jetboat hulls in the past, I had a bank of heaters set up to soften the PETG. you will need to raise the heat slowly and evenly after taking care to start with very dry plexiglass. Many plastics absorb water from the air.
A logo... I would be wary of using paint. It will likely put weaknesses in the finished epoxy. I've used laser printer cut out paper pieces before which don't bleed in epoxy resin, you could try the same with colour printed paper but mage get bleed during infusion you'd have to test. The paper I've used soaks up the resin and goes almost transparent under the glass. Keep us posted with your progress!

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Re: Lightwind kiteboard build, planing ahead

Postby rynhardt » Wed Jun 27, 2018 2:22 pm

First .. decide why you want to build your own board.
If you enjoy the construction process, great. You will get the opportunity to work with new materials and build new skills. You may or may not end up with a great board.
If you just want a different board, it will be cheaper to just buy one or even have one custom made.

If you do decide to build, once again ask yourself why you want to use carbon.
If you've always wanted a carbon board, for the either the looks or for bragging rights, then by all means go for it.
Otherwise glass is perfectly fine and popular for good reason.

Wood is fine as a core material, but structural foam works just as well, is lighter and easier to conform to a specific rocker.
With wood you may need to exaggerate the rocker to compensate for spring back. And the spring back you'll only be able to quantify once you've built your first board. Or just guess and be happy with whatever result you get.

A slight concave (i.e. 1cm over a 50cm width) will not have any significant effect on grip or upwind ability. It will make the board slightly stiffer (which is good in your case).
Forming a single concave with acrylic (or preferably polycarbonate) on your rocker table is as easy as putting spacers in the middle and pulling down the sides.
Even though forming a concave is easy, I prefer a flat board because I like flex. Your preference is for stiffness so by all means use concave.

Good luck and good winds!

phuqit
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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Wed Jun 27, 2018 6:06 pm

Thank you guys for your input and helpful advice. My reasoning regarding the size: it's quite often that we get 6-8 knots of wind, and the water is too shallow for hydrofoil. 21m kite with a door is a proven solution for this. And since I have a few minions who want to start kitesurfing, having a large board + 12m kite is much easier to get going; talking from experience. Most of the time I'm pretty happy with just my 139x43 board. But since I have to travel 250km one way to get on the water, a saved session is gold. Provided I get more proficient with board building, I may one day build a hydrofoil as well.

re: building versus buying... I like to learn new things and skills. I have time and resources to spare, so I can invest some of it to supplement my kitesurfing hobby. I don't expect to build the perfect board the first time - at the moment I have materials for like 5 boards, and I'd be happy to come up with a couple usable boards from the lot (except the cores... getting paulownia and PVC foam is both problematic and ungodly expensive here in Lithuania - even though there is a DIAB (think - divinycell) factory 150km away). So I've just picked western red cedar - easiest to obtain locally. Brokite approach is very appealing too -they make it look so easy, but I'd have to source some foam first.

Carbon vs FG - I tried a number of different boards, and I liked the carbon ones somewhat better (probably my weight plays an important role here). F-one Trax, LiquidForce Element Carbon - I liked their flex a lot. But I'm not discounting FG - especially considering it's so much cheaper.

Two sided resin infusion is supposedly a bitch, I am aware of that. I watched the videos from easycomposites - they keep some spacing between the wood planks by using 'dots' of hot glue - maybe that would work here as well, although it might introduce problems when CNC machining the panel to thin the rail parts. I'll make a few 'dry' runs first to ensure that this can actually work. The empty spaces will be filled with epoxy during infusion anyway, right?

At the moment, I'd be happy to clone the flydoor5 (which I'll have at my disposal in a few days) - keeping same dimensions, rocker, and concave (if any).

PU rails - I read a lot of ugly things in this forum :) Maybe try a small scale experiment first to see if it works at all. Since it's a lightwind board, maybe just wrapping the edges with FG could work. I'm willing to experiment, especially since you guys already paved the way!

Again, thanks a lot for your advice.
pq

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Re: Lightwind kiteboard build, planing ahead

Postby Skywalker7 » Thu Jun 28, 2018 1:30 pm

Hi,
I rode the Flydoor L and XL both. I am ca. 97 kg. In very light wind XL is good but otherwise I always felt that a 160x45-46 cm would be the perfect board. So If I were you I would make the Flydoor XL in a 160x46 cm shape with no center fin, just the fins moved a bit on the edges. Right now I am riding a Spleene Door 159x45 cm and it feels a little bit faster and more efficent than the Flydoor L since it has no center fin.

phuqit
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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Thu Jun 28, 2018 3:34 pm

This has crossed my mind as well, and I might reconsider the lower size, but the fact that I'll have the XL one at hand and be able to take all the measurements, is too appealing. Again, this is just the first of 5 boards I have planned, provided it doesn't suck, it has a potential new owner already :)

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downunder
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Re: Lightwind kiteboard build, planing ahead

Postby downunder » Mon Jul 02, 2018 4:57 am

Since quite big board, I would think of making more fin inserts for testing latter on. You can always fill the inserts with epoxy when finished.

Getting the perspex to bend is actually trivial, including a concave. Which is just a few layers of balsa on top of perspex, protected by mylar.

From here: http://kiteforum.com/viewtopic.php?f=107&t=2387451

Image

Image

The important part, as mentioned many times, is not to glue the strips before the vac all the way through. This can be seen on 2nd pic on the link as tiny gap.
Or, you'll have a significant spring back.

I would stay put from the resin infusion, no matter what, unless you have it dialed in 100%. As opposing to a closed cell, the wood strips are resisting to a vac foil and the forces here are double - one is a vac force on wood and the opposing is the bent wood forces = huge! This tends to rip the vac bag off. And when this happens with infusion, the project is ruined.
This plus other reasons is that a pneumatic press is used = 80-100psi force. And that is double the 30 inHg.

Good luck.

PS
Re PU you can read on my blogs as well. Since you have access to molds, the PU should be easy. I am puzzled a bit tho with the shallow water, wouldn't it be better to use a race board anyway?

I own the FS Razor, specially for that.

phuqit
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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Mon Jul 02, 2018 1:07 pm

Downunder: I've read everything I could find here and in other places regarding the kiteboard construction, and your blog and posts here are very helpful and insightful, I feel much more confident now rather than just starting from scratch. I'll try a few test runs using different materials and layups, and only attempt a proper build once I'm confident it can actually work. All the materials and equipment finally arrived today, so I'll start experimenting right away. Thanks again!

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downunder
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Re: Lightwind kiteboard build, planing ahead

Postby downunder » Tue Jul 03, 2018 5:15 am

No problem.

Let me know if you need SS inserts, I can send from the EU next month (maybe more expensive) or from AU shipping for around AU$8 (10 inserts).

D.


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