Breaking my boards - help needed

[grisen]

Hi board builders,

I need some help improving the strengt of my TT boards. So fare I have broken 3 boards this year, which is a little to much from my point of view I'm 90kg heavy, and sometimes my landing are hard and flat:-) the different lay-ups I have used (and crashed) are: (Bottom - core - top) (GF=glasfiber, CF=cabon fiber)

1) 3x160g GF + 15mm 80kg/m^3 PVC core + 3x160g GF
2) 1x160 GF + 1x240g CF + 14mm 80kg/m^3 PVC core + 1x160g GF + 1x240g CF
3) 1x160 GF + 1x240g CF + 13mm 80kg/m^3 PVC core + 2x160g GF + 1x240g CF

I have just started a new board, in which I have planed the following lay up in order to improve the stregth:

a) 2x160g GF + 1x240g CF + 12mm PVC core + 3x160g GF + 1x240g CF

I consider to reduce the core thickness to 11mm in order to reduce the stiffness.

Thank you in advance

Kind regards from Denmark
Lars, the board killer

[handy]

let me guess,all your boards did crack first on the top under your heels.
2nd guess : your glass orientation is 90°/0° ?
Try for the top , 3 x 250 gr 45°/45° and you will be on the save side, if you want a bullet proof board add a +-100 gr Kevlar under you heels ( core, kevlar,glass)
for the bottom go with: core 2 x 165 gr glass, 240 gr carbon and a 80 gr glass as protection over the carbon.

this will give you very solid board.

[grisen]

Hello Handy,

WOW!!!!

I'm impressed. You are 100% right, both about location of the cracks, and also that I'm using 90/0 fiber orientation.

I just have one extra question: I assume that the 45/45 orientation is only needed/demaned for the top layer(compression), for the bottom it is still ok to use 90/0 oriented fibers (only tension). I ask because I still have some square meters of 160g 90/0 GF in my workshop

But thank you very much for your help, I really appreciate you help.

kind regards
Lars

[plummet]

I'll start off by saying I haven't build a kiteboard yet. But i have build nemerous skateboards and a landbaord that flexes 130mm and bottoms out on the ground without breaking. Infact i have had no failures in all my builds. the techniques are very simalar. infact the landboard is quite abit more difficult than a kiteboard.

I say use Uni-direction mainly with a couple of layers of Double bias on the 45. Matt in either glass or carbon is the weakest form of layup. All the fibres need to go in the direction you want. 90\0 as handy states is pretty pointless. 50% of 90/0 matt fibres are doing nothing. So..l Uni directional will give you the strength lengthways. double bias on the 45 will get your torsional strength.

Get rid of the pvc core and use a more flexible/durable core. Bamboo is the shiz.

[handy]

sure you can go with 90°/0° on the bottom, the 45°/45° on the top makes the board solid cause you have to break twice the fibres than with 90/0.
Your Airex core is fine, the only thing is you have to add all strenght with the laminat That's also the only reason way the all the mayor companies work with wood, it is way cheaper and easyer to bild a rock solid board, but it does not say a better board.

[Bille]

Hi board builders,

I need some help improving the strengt of my TT boards. So fare I have broken 3 boards this year, which is a little to much from my point of view I'm 90kg heavy, and sometimes my landing are hard and flat:-)
...

Under the heal of your foot ...
before placing the second skin on your board ; cut a groove in
the core down to near the bottom skin,and lightly sand the skin itself
at the bottom of the groove. The cut only needs to be an inch or co past
where your heals are located.
THEN
insert an exterior or marine ply, (only 5mm thick is needed) into the pre-cut
& sanded groove. Then continue on with your lay-up.
50K uni will also work.

This will keep the core from crushing under your heal; and it's Much
lighter than extra and unnecessary skins !

This was the First glass & carbon board i made off a mold that actually worked,
(also the one i learned on). Turns out, the turned down rails would hold my 11M Ozone Edge
in a 35mph wind ; my 10M PL in a 42mph, even though the board was 160 X 48.
I learned to jump on that board, & when my 210lb would hit the water the board
held up nicely. It Had the groove cut with ply inserted.
The board weighed nearky the same at my 142 underground and had a 3lb pound
density core in it.
Bille

[plummet]

Hi board builders,

I need some help improving the strengt of my TT boards. So fare I have broken 3 boards this year, which is a little to much from my point of view I'm 90kg heavy, and sometimes my landing are hard and flat:-)
...

Under the heal of your foot ...
before placing the second skin on your board ; cut a groove in
the core down to near the bottom skin,and lightly sand the skin itself
at the bottom of the groove. The cut only needs to be an inch or co past
where your heals are located.
THEN
insert an exterior or marine ply, (only 5mm thick is needed) into the pre-cut
& sanded groove. Then continue on with your lay-up.
50K uni will also work.

This will keep the core from crushing under your heal; and it's Much
lighter than extra and unnecessary skins !

This was the First glass & carbon board i made off a mold that actually worked,
(also the one i learned on). Turns out, the turned down rails would hold my 11M Ozone Edge
in a 35mph wind ; my 10M PL in a 42mph, even though the board was 160 X 48.
I learned to jump on that board, & when my 210lb would hit the water the board
held up nicely. It Had the groove cut with ply inserted.
The board weighed nearky the same at my 142 underground and had a 3lb pound
density core in it.
Bille

Hey Bille, have you layup some carbon legs for yourself? maybe some of those springy cheeta legs to absorp the chop?