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Building HF-board; as light as possible, what construction?

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omg
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Building HF-board; as light as possible, what construction?

Postby omg » Fri Dec 02, 2016 12:30 pm

So, I have board a 20mm thick core foam, target for 125x47cm board, but then comes the questions: what is the best construction to build the board? The board should be really stiff, should I put a carbon stringer and how many layers of glass or carbon? Carbon is stiffer so that should be better, right? Other things to consider?

The main thing is to get the board stiff and most of all, really light! :jump:

Thanks!

tkettlepoint
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Re: Building HF-board; as light as possible, what construction?

Postby tkettlepoint » Fri Dec 02, 2016 12:50 pm

20 mm thick isn't very thick. This is why shinn puts the carbon plate on the bottom for the foils

But here is what I am thinking
#1 I would make a carbon stringer for it . if not 3-4 of them with abs rails
#2 4oz 2x2 twill, HM12oz uni,HM 8oz biax +-45 (so it crosses the board at 45degree,2mm soric , foam,2mm soric HM8oz biax,HM12oz uni , 2x2 twill You could UHM and the HM epoxy you can find
too
#3 I would put all this in a rocker table and pull it down and do infusion this will get the perfect mix ratio for resin to material.
#4 If done right I you should be able to sand the edges and buff them out.


this is just my thoughts
terrie
http://www.jellyfishboards.com

My 70mm boards are around the 2-2.5kgs depending on what the customer want

faklord
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Re: Building HF-board; as light as possible, what construction?

Postby faklord » Fri Dec 02, 2016 7:50 pm

Firstly I should point out I have only a little experience in board building. But what experience I do have may be relevant to your project.
I have built a 120 x 50cm board using a 20mm core.
Even though the majority of the strength comes from the skins, I think the core material still comes into play both from a compressibilty and shear strength point of view. I used a 75kg/m3 closed cell PVC foam (quite a bit tougher than the standard EPS).

The main layup consisted of:

200 g/m glass
200 g/m glass
200 g/m carbon
200 g/m carbon patch strut mount reinforcement (maybe 20cm x 40cm)
core
200 g/m carbon patch strut mount reinforcement (maybe 20cm x 40cm)
200 g/m carbon
200 g/m glass
200 g/m glass

Top surface was done in one shot with all layers wrapped around rails (vac bagged)
Then bottom surface was done in one shot with all layers wrapped around rails (vac bagged)
All layers were standard woven twill.
Also included were a couple of wooden (western red cedar) stringers (600mm x 12mm x 20mm) either side of the strut mount
IMG_2614.JPG
The result was unbelievably stiff. I could support the ends and bounce around the middle with little flex or fear of breakage.
In fact it was surprisingly stiff with just to top laminates applied.

I made a bit of a mess wrapping the rails. This needed quite a bit of sanding and i ended up covering these with another layer of wove glass tape (200g/m) but this was more for aesthetics and ding protection than strength.
Maybe relevant, the strut mount is a Ketos 'KF box middle' which was bonded to both top and bottom skins.


In my view the carbon provides most of the stiffness and the glass is to protect the carbon.
The board came out at about 2.8kg painted.
I've only had a few sessions on it but some of these have been struggling to get out through breaking waves in an onshore wind....lots of groundings and board tumbling in on the surf. A bit of a baptism of fire for a new build !!
All has held up fine so far.

I think it is more than stiff enough. Only time will tell if is strong enough (I'm a bit paranoid about loosing my foil !)


My thoughts for the next one are:
1) Don't bother wrapping carbon round the rails - I don't think its needed and its difficult to do well.
2) Probably only one layer of glass on top surface - most of this is covered in deckpad anyhow.
3) Maybe eliminate stringers in favor of an extra carbon patch top and bottom.
4) Plate mount - oversize holes filled with epoxy glass, prior to lamination, then drilled to size after lamination.

Hope this helps?

Lev737
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Re: Building HF-board; as light as possible, what construction?

Postby Lev737 » Wed Mar 22, 2017 1:47 pm

omg wrote:
Fri Dec 02, 2016 12:30 pm
So, I have board a 20mm thick core foam, target for 125x47cm board, but then comes the questions: what is the best construction to build the board? The board should be really stiff, should I put a carbon stringer and how many layers of glass or carbon? Carbon is stiffer so that should be better, right? Other things to consider?

The main thing is to get the board stiff and most of all, really light! :jump:

Thanks!
Hi!
I did build my HF board using 4 oz FG and 6 oz Carbon.
Cut the board in 3 pcs and wrapped every piece, creating the "rail".
After I put it all together into vacuum bag+eoxy...
Please look at the sketch and some pictures.
Cheers :bye:
Attachments
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HF+fuse_aboard.jpg

RalfsB
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Re: Building HF-board; as light as possible, what construction?

Postby RalfsB » Wed Mar 22, 2017 2:15 pm

I am in the process of making a board of similar dimensions (125x46cm) but mine is thicker(4.5cm). Made it from XPS foam, the bottom has 200g carbon and 110g glass, a bit more around the foil box, the top has 200g carbon + 110g glass plus the deck area has additional 200g carbon plus the foil box area has yet another 200g carbon. The edges are wrapped from both sides. The board also has a bunch of footstrap inserts. So far the whole construction seems to be pretty stiff and strong. The weight is nearly 2.9kg (this includes a built-in KF box). I did not use vacuum (with that I would probably saved a bit of weight).


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