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Board Blank density

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TomW
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Board Blank density

Postby TomW » Fri Nov 10, 2017 8:38 pm

I'm having trouble getting surfboard blanks milled for hydrofoil boards. So I'm considering using 3 layers of 10mm Divinycell glued together with rocker bent in while gluing.
My question is if I should use 45kg/m3 or 60kg/m3. I'm looking to build a few light freestyle / Freeride board. 1350 and 1200 long.
I'll laminate with unidirectional-carbon-fibre on deck and bottom followed by Glasfiber wrapped onto rails. The foil attachment with have 80kg/m3 insert patch and screw strengtheners.

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tegirinenashi
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Re: Board Blank density

Postby tegirinenashi » Fri Nov 10, 2017 10:18 pm

If you are putting three layers, then one sheet of 45kg/m3 in between the two 60kg/m3 would provide the best strength/weight.

TomW
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Re: Board Blank density

Postby TomW » Fri Nov 10, 2017 11:11 pm

My calculations :
All H60 blank is 900g
All H45 blank is 702g
H60 outside and H 45 middle is 858g.

This is based on rough calculations using 130cmx 40cm rectangular board outline.
I designed a board in CAD and the rough calculations are very close to the real 130x47 board with curvature and taper at nose.

The H60 has 30% more compression and shear strength.

TomW
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Re: Board Blank density

Postby TomW » Fri Nov 10, 2017 11:18 pm

My lamination schedule is planned to be :
Option 1: 2 layers of 250g uniD cf, 250mm wide, and 2x 200g glass each side
Option 2: 3 layers of 250g uniD cf, 165mm wide, and 2x 200g glass each side
Option 3: 4 layers of 250g uniD cf, 125mm wide, and 2x 200g glass each side

I'm cutting the uniD cf from a 1m wide piece, so I can decrease width and increase layers,
I'm guessing the 125mm wide and 4 layers is the best stiffness.

I'm not planning on using any stringers.

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Re: Board Blank density

Postby BWD » Sat Nov 11, 2017 5:26 am

I'd go with #1
Or something else that has both heel and toe of both feet over carbon, with just 2x200glass skins.

Another thing you can do is put a layer (or partial layer) of reinforcement between the foam sheets to boost stiffness without another full layer of anything on both sides. They did this in ac34 to get stiffer without extra weight - and they were already using prepregs and aluminum honeycomb. I'd put a patch around the mast attachment, maybe a 30x75 strip under the stance area -mainly if using lighter foam.

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downunder
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Re: Board Blank density

Postby downunder » Tue Nov 14, 2017 4:03 am

Tom,
your UNI is in the board length only? The bottom will be compressed under your foot with tension on top square to the board length, with only UNI binding fibers resisting this.

Thoughts?

TomW
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Re: Board Blank density

Postby TomW » Wed Nov 15, 2017 12:26 am

Yes, I'll have unidirectional-carbon-fibre running from tail to tip, on top and bottom of board.
Idea is to create a sandwich beam.
Glass fiber at 0 and 90 degrees, using twill or plain weave.
My thinking was option 3 would give strongest beam compared to option 1.

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downunder
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Re: Board Blank density

Postby downunder » Wed Nov 15, 2017 2:16 am

The local guy here is wrapping the complete board if cf. 50+ board he made, must be good.

TomW
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Re: Board Blank density

Postby TomW » Wed Nov 15, 2017 6:44 pm

Downunder,

Trying to keep cost down...


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