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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Fri Nov 22, 2013 9:35 pm 
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The core, unless a dense hardwood, should be made of laminations, with vertical grain or opposing grain direction.
Like a wood strip kiteboard core.
This gives strength and resistance to warping.
I think I might foil one side, and put at least a layer of glass on it, before foiling the other side.
Then finish laminations, bog and fair both sides...


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Fri Nov 22, 2013 10:29 pm 
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OK -- so Marine plywood to make this part, with as many lamination-s as
i can find then .
DO you like one type of ply-wood better than the others, for this application ?

One thing on the glassing of just one side at time :

Epoxy will shrink as it cures ; if you only coat one side, then that
side is gonna get smaller as the epoxy cures. Same thing goes
with a foam core, if you laminate one side then that side will
get slightly concave as it cures, and glassing the other side may or may not
make the first side straight.
The larger or Longer the part, the more prevalent the shrinkage will appear.

You Can however, lay-up a part in a mold or caul-plate , and only glass
one side of the core at a time, but the second side should stay under
vacuum until it's completely cured. This is normal when the core needs
tweaking before the second skin is attached.

Watch what happens when you wet both sides of a ply-wood, then set
it in the sun and dry just one side ; the sunny side goes concave.

Bille


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Fri Nov 22, 2013 11:49 pm 
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If you are going for a composite-heavy build, okoume ply could be good because it's light and easy to shape.
If you want heavier on the wood, and lighter on the composites, birch would be good.
Or the bamboo as guys have done above.
For max plies, stack sheets of 3mm into a blank, this would give about 1 ply per mm or thickness.
I think this method, with a transverse spar cap of uni's, and a skin of +/-45 stitched CF cloth, would be very strong.
Birch advantages:
cheap - <$20/sheet from guys that supply cabinet shops.
strong - probably you would not have (as) catastrophic failure on hitting things.
fast -no need to laminate so many strips.

But the okoume would be lighter. and easier on the sander and router.
You also could do strips of poplar, pine or cedar for the blank, and laminate on a little more CF.
Cedar is nice except for the sneezing.

Short answer is I'd probably use birch, though.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 1:45 am 
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BWD wrote:
...

Short answer is I'd probably use birch, though.


Birch ply it Is then ; Thanks !!!
I'm hoping to find one with Lots of lamination-s ; the plys
look like a topographic map ; makes final sanding/shaping easy !!

Bille


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 3:19 am 
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Location: Southwestern Ontario
Bille wrote:
BWD wrote:
...

Short answer is I'd probably use birch, though.


Birch ply it Is then ; Thanks !!!
I'm hoping to find one with Lots of lamination-s ; the plys
look like a topographic map ; makes final sanding/shaping easy !!

Bille


Look for birch veneer core. No voids, lots of layers.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 8:48 am 
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Marine Grade Baltic Birch is the way to go (if you can find it):

Image


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 9:33 am 
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friend tried the 15mm ply wings i shaped behind his ski- worked which is good considering they were $5 each to make but a bit draggy.. then the ski broke down again - r&d getting expensive...

injection moulded abs wings @ 11mm thick? --..suuup chaep and easy to produce? maybe too flexy tho - but there are some stiffer glass filled ABS compounds out there that are quite amazing from what i have seen... FEA model

$3000 foil boards and $2900 race kites are not exactly making kiting more accessible for youth.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 1:13 pm 
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The UA4085 louvre aluminium extrusion looks about right for a mast? 94mm chord and 10mm thick.
Australian company.

http://www.ullrich.co.nz/images/louvre_3.jpg

It seems Australia is the place to live to build hydrofoils.
These are PVC wings which mount onto a stainless steel tube for strength.

http://www.thebackshed.com/windmill/PVCBladeOrders.asp


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 2:26 pm 
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I wonder if you could buy one of these and layup over it with epoxy to make the hydrofoil fuselage and tailplane?

The wings look quite similar to the Taaroa Sword.

http://www.aliexpress.com/item/free-shi ... 68799.html


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Nov 23, 2013 3:41 pm 
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Location: rhode island
thanks ronnie.
...so close

somebody has the right piece laying around, but its easy to understand why folks start from scratch.

@Hawaiis
i've probably missed it in past post.
what is the chord length and thickness of your koa strut?
have you added any glass to the strut?

any opinions regarding the stiffness compared to Europ2 numbers?

my guess is that you'd need something 1" thick or greater to match his numbers.
so i was wondering what your impressions are when comparing the ride of wood foils on a wood strut vs the carbon strut

thanks again.
-bill


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