Building a light wind board

30 posts in this topic

Yep, I'm thinking of building a light wind kiteboard. This will be my first attempt at building a kiteboard so I'm trying to keep it simple (and cheap), but also don't want to have to build it again after only a few uses. So I'm after a bit of advice and ideas from those who have gone there before.

the basic plan a broad 1600mm x 500mm. Use a bottom layer of 4mm hardwood ply brace and a top (smaller) layer of 7mm construction ply. Glue them together with epoxy resin. then coat the entire thing in fibreglass and epoxy resin. I'm hoping that the 4mm ply on the bottom will still give a bit of flex on the tips and the 7mm will stiffen in up through the middle. Hopefully it won't weigh a ton either.

some of my questions are...

will it work or just snap in half?

is the size too big? Too long? Too wide?

is normal woven fibreglass ok? Was thinking 1 layer of 200gm.

How should I taper the top layer of ply to the bottom layer so as not to create a stress point? There's a picture below with 2 options of how I was thinking of tapering the ends of the top layer. Which would be better?

obviously there is going to be fins and straps on there somewhere too.

image.jpeg

 

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Right, this is a bit of fun :D  Couple of the guys I used to kiteboard with built their own boards, large and small.  

  1. You're a lightweight, no need to go so heavy duty.
  2. If you're going to glass it then reduce the bottom and top board thickness, it's going to add a heap of strength.
  3. Bring the top layer in from the edges, giving you more of a thinner rail to grab the water.

I'm not sure if using plywood is ideal, I remember a conversation with a few of them mentioning that over time flexing the plywood the glue inside starts to break down.  You're better off getting thin sheets of wood yourself and building the core up from there.  I know some people just go with the thicker wood, but building it up will give you some flexibility to thin it out layer by layer as you get further to the tips.  It will also save a heap of weight on a huge light wind board.

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The picture you showed either only shows one half of the board or is a unidirectional board, which is it?

What conditions do you intend the board at? Ie the surf or some spot where it is super flat. The reason being, if the conditions are flat without chop, you can go for a much simpler design, just head off to Bunnings and get some pine wood 19mm thick planks and edge glue them with West System resin to the desired width. Make sure to get a router jointing tool for a finger joint. I have a thread some where describing the build process.

 

If you go down the ply wood laminating route, expect a lot more work and equipment. Where you have ply drop offs do not leave abrupt step changes in thickness, that is exactly where it will break. To keep the weight down, you will need to squease the bejesus out of the laminates to push out excessive resin, otherwise it will be too heavy. When getting the ply or even the thin sheets of  wood, get good quality other wise all you hard labour will amount to two or more boards --- with a ragged break where you once had one board.

If you go down the route of 19mm planks, check for wood knots, warpage etc. Don't be afraid to stand there for 15 minutes pulling one plank out after another until you have the perfect set. The basic tools you need are a hand saw or jig saw, hand planer, coarse file, sand paper, ideally a cabinet makers scraper, three or so LONG clamps (to keep the planks together edge wise whilst the resin is setting). Oh forgot a router for doing the edge joint finger cut.

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@.Joel when I was doing the "flex test" at bunnings yesterday I didn't consider how much extra the fibreglass would help. So maybe just 2 layers of 4mm will be enough?

the top layer is going to be 25mm in from the bottom to give a thin rail.

@SoutherlyBuster yeah, each end of the board will be the same. The plan just shows 2 different options for how to round off the top layer so that it (hopefully) won't creat a stress point. Or would it be better to just taper it down to the bottom with no rounded ends?

i kite in Morton bay, so it's flat water, but it's not glass, we do still get a bit of chop.

i can see the benefit of the "bunnings plank" :D but I think I'm going to stick with the plywood. The stuff I'm looking at is structural ply so it has limited defects in the wood. Also I'm going to use my hilux as the press, so it should get most of the excess resin out.

 

Does anyone know about fibreglass? Is the standard woven ok? What weight? How many layers?

i don't want to vac bag it, so is rolling it ok?

 

also reconsidering the size. maybe I should go a bit shorter to help reduce the weight and risk of breakage.  1550mm X 470mm???

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160x50 is super massive. My homemade coffin lid is 145x45 and that's big enough.

Don't use the 7mm. use 2 x 4mm layers. Taper the ends of the top layer and round them as per the left hand side of your picture. That will reduce the stress riser and chance of failure.

I suggest a token rocker. maybe 20-30mm. You can press the rocker in when laminating the 2 plywood layers.

My coffin lid has a lot of rocker in it for a light wind board. That's because I sometimes take in out in up to double head waves. I sacrifice some upwind ability for better wave riding ability.

 

Note i'm only using the 2 heal side fins these days.

 

PS my board is made from 5mm vlam bamboo with 600grm triaxle fibre glass.

 

 

 

 

 

 

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jhn.holgate, .Joel, Chook and 1 other like this

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cheers plummet.

so, new plan. 2 layers of 4mm ply. smaller size (155x45), and a bit of rocker.

@plummet would you recommend the 600gm fibreglass, even though its got a thicker wooden core? does your board have much flex?

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No 600grm will be too much with a 8mm core. Maybe drop down to 300 grm

My board flex is ok for what it is. It I did it again I would taper the ends of the board down to 2-3mm. Having a 5mm core at the ends of the board means there isn't enough tip flex.

BUT. For your first build a light wind stormer is a good choice. Get in there and give it a go. Learn and try different things on your next build.

Check out these 2 forums for board building. There's masses of info there

http://www.kiteforum.com/viewforum.php?f=107

http://www.boardbuilders.co/p/forum.html

 

 

 

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Fibre glass, stainless nut inserts, epoxy and some milled fibre to thicken the resin when laminating the ply (is this right?) all ordered :D 

Quick question. What can I use to plug the treads of the nut inserts while I put the fibreglass on?

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blutack, plastasine, playdoh... even silcone. 

i use glue powder to thicken the resin for laminating the wood layers. 

andy666 likes this

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Did my first test run yesterday and it was a failure. 

I just tested on a small section of timber, with some paddle pop sticks on it, to see how well the fibreglass would stick and form to shape. I also wanted to test my cheap vacuum system, which is just a hose attached to the deflate port on my kite pump.

well the entire thing was a failure :( 

the kite pump pulled a good vacuum down to about -0.8 bar, but I couldn't get the bag to seal so it would hold vacuum for more then about 20 seconds.

then when I unwrapped it this morning I was not happy with the fibreglass. It didn't form well around the paddle pop sticks (this could be due to the vac failure), and it didn't stick to the timber very well. It looked good to start with but when I gave it a flex test the fibreglass started to unstick (you can see in the pictures where it has unstuck and turned white). I then just grabbed an edge and it peeled easily off the timber. I know @plummet only puts his fibre glass to the edge and not around, so there must be a way to make it stick?

What am I doing wrong? 

I messured the resin using a digital kitchen scale, so I know the mix ratio was right. I wet the timber first, lay the fibreglass on top and then finished wetting out the fibreglass until it was clear.

did I absorb too much resin out when I vac bagged it? I just used peel ply and a breather layer over the fibreglass.

do I need another layer of resin on top of what is there to so help seal it better? But doesn't that defeat the point of vac bagging?

Please help :cray: 

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Progress update.

i picked up an old fridge compressor for free during the week to use as a vacuum pump. Last night I rewired it and gave it a test run. Can easily pull down to -0.9 bar. I then ran it for 3 hrs at -0.5 to check if it would overheat. No vacuum switch or tank at this stage, just running a bleeder system (bag not 100% sealed) Worked ok, so today I put it into service. 

Laminating the 2 layers of ply together for the core. Clamping them at -0.5 bar, which is wellover 2000kg of force over the surface of the board. 

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Fingers crossed its works. 

Chook, .Joel, ssayre and 1 other like this

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Stage 1 complete. Core laminated successfully. I had it flexed to 35mm rocker when under vac, which had come back to about 18mm. Not too bad. 

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.Joel likes this

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31 minutes ago, plummet said:

Every man needs a stainless rule!

They got banned when I was at high school for having sword fights with them :D 

 

1st layer of fibreglass on the top of the board is currently under vac. That was stressful stressful :fear: 

I had everything prepped and ready to lay on, but it was still a race against time. Mostly because I mixed up 1 batch of epoxy and thicken it with milled fibre to fillet the edge of the top layer of ply so the fibreglass would have to press into a sharp corner. Then had to quickly mix another batch of epoxy, get the fibreglass on and under vac before everything started to cure.

but I got it done and it's currently sitting at -0.3 bar. Hopefully it turns out ok. 

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@andy666 that first layer looks like it turned out well.  Stick your name/number on it before you put the final layer on :good: 

@plummet did you design those foils or is there somewhere online you can pickup info on them?

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13 hours ago, plummet said:

 

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Looks like you heat seal your bags. What are you using?

i tried heat sealing with a couple of cheap eBay bag sealers, but couldn't get a continuous seal. So I gave up and just used clear packaging tape. 

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2 hours ago, andy666 said:

Looks like you heat seal your bags. What are you using?

i tried heat sealing with a couple of cheap eBay bag sealers, but couldn't get a continuous seal. So I gave up and just used clear packaging tape. 

It's my patented secret bag sealing procedure!

Soldering iron and a solid straight edge.  Use a soldering iron with about an 8mm round tip or maybe even bigger. The pissy little ones for small electronics don't melt the bag fast enough. 

The trick is to do one continuous melt from one end of the bag to the other. Stopping and starting can lead to vacuum leaks. 

Do a couple of test runs first to get the process. Once sorted its relatively easy. I even seal the last side of the  bag like that after putting the parts in. Takes about 5 mins. 

 

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well, I think it may be finished. it didn't turn out as good as I was hoping, but not bad for a first attempt.

last week, after vac bagging the fibreglass it looked quite dry, so I put on another couple of coats of resin to help help seal it all up. This caused a lot of runs in the resin, which honestly I couldn't be bothered sanding out.

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Today I painted the board to help protect the resin from UV light and to hopefully make it look a bit better.

I just used whatever paint I had in the garage. So its got a base coat of gloss white on both sides. The top is satin black with gloss red misted over it. The bottom is gloss red, with black misted over.

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I'll weigh it tomorrow, but Im guessing it around 5kg.

jhn.holgate, .Joel and Kamikuza like this

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Just got back from a quick test ride. In a word? Brilliant! :clapping: 

The wind was only 8 knots, so I put up my 15m speed 3 and headed out. A quick dive with the kite and I was up and going. The board was really nice to ride and staying upwind wasn't a problem. In fact, after about 20 minutes the wind picked up to about 10knots and I had to half depower the kite. At a guess, I may be able to get going in 6 knots if I dive the kite hard to get up on the plane.

there was a little chop as well and I could feel the board flexing under my feet and just smoothing everything out. 

I have always preferred light wind kiting, but I think I'll be disappointed now when it gets above 12 knots. 

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The next job will be making a bag to hold big red.

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