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 Post subject: How Thin Can I Go?
PostPosted: Thu Jun 19, 2003 10:13 am 
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Joined: Mon Sep 24, 2001 1:00 am
Posts: 29537
Location: World (KF Admin)
I have been building a lot of boards with a 3/8" (9mm) thick wood
core and glass skin. Except for the weight, I really like the way
they ride and I think the flex and lack of volume really play a big
role in the performance.

I want to make an identical shape in corecell to try to get the
weight down. If I use 9mm corecell and a heavier laminate will it
work or is the board destined for failure if I go this thin?

Anyone have any ideas on how heavy I would have to make the glass
skin?



the historically safe recipe has been 18 oz glass top and bottom on a
3/4 in core.
if you cut the core thickness in half (3/8 in), you'll need to use 4
times as much glass (72 oz) to keep the stress comparable.

-that might be as heavy as the plywood...

*******

I weigh 185 pounds, what is that about 85kg?

If I use 4 times the glass I should end up with a board that has
about the same stifness, right?
I want the board to be flexible, I just don't want it to snap in
half. How much glass do they use on snowboards? They are thin and
seem to be able to bend quite a bit without snapping.

*******

if we stick with the same example;
the core thickness is cut in half to .375",
but the skin is increased 4x (approx .1")
the board stiffness will be about the same.
possibly a little stiffer due to the high skin thickness.

I'm just guessing, but i doubt 72oz top and bottom is required.
I would consider alot less (30 oz) on the bottom and see how you like
the flex.
assuming the board is around 140cm, the stresses shouldn't be that
high.

*******

The board I want to duplicate with the foam core is 120x39

I am thinking I will use a triaxial fabric like I have heard is used
with snowboards. My understanding is that the non-woven fibers
require a lot less resin so that should help keep the weight down.

*******

That sounds pretty good.
I figure with most layups: 50% is resin and only half of the glass is
aligned for bending stress'.
The triax will be a big improvement.
If the weights are acceptable for you. I would guess that 30-35 oz.
top and bottom, with a little extra under your feet (just for luck)
would work just fine.


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 Post subject:
PostPosted: Fri Aug 08, 2003 10:27 am 
hy !

i´ve been working with 8mm herex foam and carbon laminate. 2 layers of 160 g/m² carbon on underside and on top with one layer 163g/m² glass topping on each side. works perfect.
due to the stiffness of the carbon there is not too much flex.
i´ve been riding this board for one year now, not probs with stability.

last weekend i build a 8mm herex board with a 730g/m² glass layer (triaxial) and carbon stringers. this board has a huge amount of flex, but i´m not sure wether it is strong enough. we will see after testing the board.

however, a 8mm core works fine - easy to shape and nobody really needs the extra volume on a kiteboard with a thicker core in my opinion, especially with the smaller boards that i ride (max lengh 137 cm).

cu
gerald


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 Post subject:
PostPosted: Fri Aug 08, 2003 3:50 pm 
Hello Gerald?

I want to ask you about stiffnes.

Do you use one 8mm layer of Herex?

I want to laminate 3x 3mm Herex do you think that it will be stiffer/stronger or weaker.

Have you concave on your board? This help a lot regarding stifness. /But also unequall stress load/

Do you ever build wood board?

I now make board from light weight plywood 3x 3mm core

What will be difference between same shaped board with simillar flex /deferent skin using for example glas on wood and carbor on foam/
from wood and from foam?

Will be wood cored board better?

I read somewhere that wood has ability of internal damping - thats why is still used on good skiis and snowboards.

It is is true or its BS?


I also thinking about wood herex composite.

What do you think?


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 Post subject:
PostPosted: Fri Aug 08, 2003 4:53 pm 
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Joined: Sun Nov 03, 2002 1:00 am
Posts: 393
I forgot log in
So above post wrote

Tom


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 Post subject:
PostPosted: Mon Aug 18, 2003 1:29 pm 
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Joined: Tue Feb 18, 2003 11:19 pm
Posts: 32
Location: Europe
hy tom!

actually i´m using a 8mm herex core. laminating 3x3mm herex sandwich cores should be stiffer, as long as you are using vaccum for the sandwich.

the board mentioned above (full carbon) has no concave (this was one of my first boards), the boards i am buildiung now have all a concave of about 8mm from tip to end.
it true that this ads extra stiffnes, but this is not the motivation for building a concave board - its about the riding!

i just built a full carbon/kevlar board this weekend (120 cm) and i will compare this board to the one i built about a week ago with glass (same shape - 125cm) - as soon as there is wind! the board is stiffer, but by far not as stiff as the full carbon board. (klevlar has a lot of flex).

i have to add that i use HPL-laminate on the underside of my boards wich might alter stiffness as well. next board will be a 115 with kevlar/carbon and no HPL on the underside.

concerning wood core i have no personal exp., but a friend of mine who is a snowboard designer at a well known brand built some kiteboards with wood core (about 9mm) and glass laminate plus a design layer.
i have never seen a board with more flex!! its perfect for his riding style (no chicken loop) but too much for my taste.

i have to add that you prob. will never reach this performance when shaping a wood core at home , since this guy is using computer aided machines to cut and shape the core (depending on the flex you like). and this boards are quite heavy - no prob if you ride wake style.

dont know much about the damping - effect f wood in laminate, but if you look at serial boards they often got wood parts under areas of punctual load (like under the footpads). probably the wood spreads punctual load over a wider surface!?

i think that a wood core might give you more flex but on the expense of much extra weight. concerning stability a well built PVC-foam-core board will be strong enough - with much less weight.

hope this helps
cu
gerald


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 Post subject:
PostPosted: Thu Aug 21, 2003 8:32 am 
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Joined: Sun Nov 03, 2002 1:00 am
Posts: 393
Thank you very much Gerald. For answer.
Please read some review when you are try carbonkevlar board.
Something like Carbonkevlar vs Glass vs Carbon.

Regarding concave. I built on my board ca 10mm concave in middle with continual fade to tip so tip has no concave at all. I think that concave added grip but also create drag and slow board down. I like fast board and so i thinking about cancel concave at all.

What are you experiences with concave?



Thank you very much

tom


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 Post subject:
PostPosted: Fri Aug 22, 2003 8:56 am 
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Joined: Fri May 24, 2002 1:00 am
Posts: 338
hi

i finished this week the construction of my latest board.

some technical data:
it is 96 cm long, 39 cm wide and has a concave bottom that is increasing towards the tips.
the concaves are about1.5 cm in the middle and grow to about 3.5 cm at the tips. rocker is about 3cm on both sides.

the idea behind was to create a board that has very good grip, but is easy to turn, that starts early but can handle overpower well.

construction:
i used 3 layers of 1.5mm plywood and 2 layers of 166g/m2 crossdirectional fiberglass, one of the layers cut in 45°. the core became this way a wood/glass/wood/glass/wood sandwich. the tips with the stronger concaves, i reinforced with one layer of crosscarbon 166g/m2 on the bottom side. finally i put one layer of 100g/m2 glass to finish. (of course, the whole lamination is done with epoxy)

the board weights this way, without pads and straps, about 1.6 kg. complete, it weights 2.1 kg which i consider absolutely alright.
i already tested the board behind the wakeboat. first impression: it is very fast compared to the wakeboards i usually use, but ways more aggressive when edging and turning.

this weekend, i will test it at the lake silvaplana. if we are lucky and there is wind, i can tell you more about the performance with the kite on monday.

regards, mede


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 Post subject:
PostPosted: Sat Aug 23, 2003 8:44 am 
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Joined: Sun Nov 03, 2002 1:00 am
Posts: 393
Im looking forward and im very interesting

Tom


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 Post subject:
PostPosted: Mon Aug 25, 2003 10:01 am 
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Joined: Fri May 24, 2002 1:00 am
Posts: 338
hi everybody

so, actually i was lucky with the wind this weekend :) at lake silvaplana, it was blowing 4-6 bft , i was out with my 16.5 gxr almost 8 hours, so i can tell you more about the board.

overall impression (as far as i can tell after 2 sessions on it)
most importantly, it works! the more overpower, the better. as with most boards, you have to get used to it a bit to find the right position of your weight.

to make it going, you have to accelerate it a bit more than e.g., my 140* 40 board, i.e., going 20 meters or so slightly downwind to pick up speed. probably due to the very concave bottom, there are like 2 stages, first, you get out of the water, and second, a „turbo“ kicks in.
once on speed, you can edge as hard as with no other board i know, and you go upwind at an incredible angle. (under the condition that you have power in the kite). because of the excellent edging, you can handle overpower incredibly well.

on the other hand, when it is gusty and the wind decreases immediately, you just sink (no wonder given the small size of the board.)
do to its small size the board is very loose for switching. to jibe it, you need a sensitive foot as it reacts very quickly.

the jumping ability are of course cool: you can really load the kite, and you don’t even feel the weight of the board when the lift kicks in.

in conclusion, my hopes that the concept of an ultra thin, ultra concave, very short & wide board would work have been confirmed :)

regards

mede


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 Post subject: ITCHY-SCRATCHY SHOW
PostPosted: Tue Nov 23, 2004 9:00 pm 
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Joined: Tue Nov 23, 2004 7:42 pm
Posts: 7
using the pvc and resin core I often go to less than 1/4(finished) inch rails ,but retain tons of flex(softer ride)and viturally unbreakable


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