Here you can exchange your experience and datas about your home build boards
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shawn13
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Postby shawn13 » Sat Jan 09, 2016 1:16 pm
Looks awesome!
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rynhardt
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Postby rynhardt » Tue Jan 12, 2016 10:59 am
Another short video of mostly the board and my feet
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Lokihel
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Postby Lokihel » Sat Jan 16, 2016 2:51 pm
rynhardt wrote:For example, when edging the board forms a natural concave. And I suspect that when landing it forms a natural convex.
I think you only ever get a convex bottom, since in both cases your feet are pushing down on the board.
When edging because your feet are pushing into the board, you will create a convex shape on the underside of the board, which is probably not too good for going up, and overall stability.
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rynhardt
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Postby rynhardt » Sun Jan 17, 2016 8:05 pm
I think it might be convex as long as it is pushing against water. The half that's in the air bends the other way.
I don't know how much convex or concave contributes to stability once the board is edging?
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Lokihel
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Postby Lokihel » Mon Jan 18, 2016 6:08 am
It affects upwind performance mostly.
Imagine an extreme case where your board is so convex that the bottom is actually half a cylinder. You won't be going far with that one.
The extreme of concave is harder to imagine, yet it is easy to see that when you have an exaggerated concave, you will have the heelside of the board vertical (which will grip in the water like a keel) and the toeside horizontal (which will deflect the water).
The concave would then help you go upwind better. It probably has other effects that are harder to picture.
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rynhardt
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Postby rynhardt » Mon Jan 18, 2016 9:58 am
In the extreme cases you mention, agreed the difference between convex and concave is substantial. But given the tiny amount of concave on most boards, I think the effect is minimal.
You may gain 1 or 2 degrees of angle to the water with the concave which is trivially compensated for by edging slightly harder.
And unless the other edge is also in contact with the water, i.e. when the board is ridden flat, there is no compression or additional lift provided by the concave.
*edited to fix the labels on the image
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- flatvsconvexvsconcave.png (7.66 KiB) Viewed 2935 times
Last edited by
rynhardt on Tue Jan 19, 2016 10:23 am, edited 1 time in total.
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Lokihel
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Postby Lokihel » Mon Jan 18, 2016 2:23 pm
I agree. The difference between a 'flat' board and a board with a standard concave is small, although it does help a lot for marketing
And btw, you got concave and convex the wrong way around on your picture.
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rynhardt
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Postby rynhardt » Tue Jan 19, 2016 10:27 am
Yeah, there's a lot of marketing BS around.
And I fixed the labels..
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lovethepirk
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Postby lovethepirk » Mon Apr 25, 2016 7:27 pm
Rynhardt,
The the VHB tape hold the fins? I know how strong that tape can be but I was curious with how skinny fins are if that tape has enough material to adhere to.
Also, would a flat poly board with only bindings and fins create a rocker by just the weight of the rider?
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rynhardt
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Postby rynhardt » Mon Apr 25, 2016 9:32 pm
Amazingly enough the VHB tape was enough to keep the fins attached to the board. The strip of tape is the size of the base of the fin.
That being said, I used small fins with a big base. I think bigger fins with a smaller base may need bolts.
An unsupported polycarb sheet would be unusably flexible at low thicknesses (5-10mm), and very heavy at thicknesses high enough (20-30mm) to be useful. Polycarb is also heavier than water.
But yes, with just the weight of the rider, a flat polycarb board would have rocker under the feet and camber (negative rocker) between the feet, somewhat like a snowboard.
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