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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Sat Jun 08, 2013 5:05 pm 
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okume plywood is too expensive 4 my budget on this project


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Sat Jun 08, 2013 7:39 pm 
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BWD wrote:
Stitch through idea or many stringers might be too heavy and stiff for sup I think. I would just do a sandwich deck of 2-3mm high density foam (corecell or d-cell etc) or thin okume plywood, veneer etc.

Frederiks idea is correct in a way but only partly.
Its right mainly IF he means having a sandwich deck AND sandwich bottom. But many board builders have known for many years a sandwich deck helps against impact and heel dents.
By making the laminate thicker it is stiffer and resists impact. The recipe is different to maximize stiffness and light weight.
For example:
stiff and light = eps core, 2 oz glass, core cell, then 4-6oz glass on top. This sandwich can wrap the rails and deck
Impact resistant = eps core, 4-6 oz glass, THIN corecell or ply or veneer ( or even just a thick hot coat), then 6-8 oz glass on top.
Or you can just add a few glass layers on deck!


A sandwich construction gives you better specific stiffness for the part it does not help with impact resistance. You want the strongest construction at the areas where you are moving around on the board, only a thicker skin is effective here.

http://en.wikipedia.org/wiki/Sandwich-s ... _composite


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Sun Jun 09, 2013 1:28 am 
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And a sandwich skin is thicker, so resists buckling better, which is what is needed in this case :wink:
A thin sandwich deck resists impact and point loads well but does not necessarily make the whole board too stiff.

Also important, modulus of resin and core....


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Sun Jun 09, 2013 11:23 am 
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I understood it as if the #0 already has a SUP which works and wants to upgrade it to kiteboard use.

You could do a sandwich but it only adds bending stiffness. Most of the SUPs I have seen are sufficiently stiff due to the height between the bottom and top of the board.

It is ok for the stand area to flex a bit and therefore adding more stiffness is not the goal, adding strength is due to the fact that you are jumping/falling on it.

A traditional sandwich consists of fiber laminate skin layers for strength, a light weight core to space the skins apart. The core just has to be sufficiently strong to cope with the shear force that comes from the two skins bending with one under compression and one under tensile loading.


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Sun Jun 09, 2013 5:49 pm 
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one off the strongest things out there, and it's light and bendable and easy to wark and cheaper then okoumé, is en grain balsa mat !

littlt cubes of let's say 1/4 inch end grain balsa on a thin layer of fibers !

you could hit it wih a hammer and it would not crack !

just an idea.


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Mon Jun 10, 2013 1:32 pm 
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FrederikS wrote:
I understood it as if the #0 already has a SUP which works and wants to upgrade it to kiteboard use..............



I dont believe edt ever specified if the board was a new build or a retro-fit.
i agree that could make a difference in the chosen approach.


something greg loher (RR epoxy) was promoting with lots of success ( despite your interpretation of the theory)

furniture grade wood veneer over 2 lb EPS foam.
light glass schedules easlily tailored to your needs.

overall very easy, fast, relatively cheap with excellant cosmetics.

http://www2.swaylocks.com/node/1029134

i think there is an instructional video buried in the thread somewhere


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Mon Jun 10, 2013 2:38 pm 
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i have a brand new usa 12'6" blank with a decent stringer built in that I'm sitting on trying to decide. After all this talk I think I might just give it an extra thick glass job and look for a padding that provides extra strength and hope the stringer provides enough strength. The plan is to load it up with kites, boards, sandwhiches, root beer and an anchor, SUP-kite for destinations unknown when it is nuking and then unpack anchor and ride the twin tip or surfboard. I'm gonna load it up like a winnebago.


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Mon Jun 10, 2013 3:13 pm 
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I second the veneer as a great topskin. You get the strength you need plus a good cosmetic custom look.


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Mon Jun 10, 2013 3:33 pm 
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here is one other idea just poped out my mind !

shape the blank

then, shape some gooves in it lenght way, let's say 3/4 of the board lenght, 2 on each side
1/8 wide, half inch to inch deep ? 1/16 would do, depending on :

- get some carbon rods same shape the grooves, and glue them inside them.

top skin shoul touch the rods once you laminate

tada

light weight stringers super rigid for the deck

AND if you have any rocker in the blank ( dont know nothing about sup shape !!! ) then you will have the stringer preloaded as you glue them in... even better


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 Post subject: Re: building a SUP how do you strengthen it for kiteboarding
PostPosted: Tue Jun 11, 2013 3:16 am 
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FrederikS wrote:
A sandwich construction gives you better specific stiffness for the part it does not help with impact resistance. You want the strongest construction at the areas where you are moving around on the board, only a thicker skin is effective here.

http://en.wikipedia.org/wiki/Sandwich-s ... _composite


Fred you are DEAD WRONG, both in theory and practice,
The sandwhich structure prevents heal denting and impact fracture much better.
if you don't believe me build up some test panels, jump on them. the sandwhich is multiple times stronger in impact with the equivalent number of plies without a sandwhich.
3 plies of 6 oz on 1lb foam will actually fracture when jumped on from a height of about 1 foot.
2 plies of 6 oz + 1/8" dcell H80 + 1 ply 6 oz on 1lb foam will have only a small dent when jumped upon from 2-3 feet.


It is stiffer yes, this stiffness and the compression strength of the structural foam allows it to distribute the load to the lower skin and soft core over a much wider surface area engaging more material and lowering the overall stress and deformation of the structure in impact.


Also to whomever suggested carbon I suggest they run the same tests. Carbon will shatter on almost any impact load when put overtop of a relatively soft structure that will be jumped upon due to it's high stiffness and minimal deformation to failure. (low impact energy to failure) It maybe suitable for the lower skin of a sandwhich where point loads are reduced but I would avoid it's use on the top skin.

Mixing carbon and glass is also not a terribly effective use of materials as the material stiffnesses are so different that the glass is effectively just "along for the ride" until the carbon fails. Really only useful in ballistics applications when you want parts of the structure to shatter and absorb impact energy and other parts to stay intact after initial failure in order to prevent penetration of the structure.

veneer has a similar effect in improving impact , but any of the veneers (oak birch) I've tested have been a little on the heavy side when compared to a sandwhich structure of equivalent impact strength

My vote, if you or a buddy have some thin dcell or core cell laying around (1/8") use this as it will get you the best strength at the lowest weight. . If not veneers should be more readily available, easier, cheaper and better looking .


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