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Thin Baltic Birch with Fiberglass reinforcement?

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buttercutter
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Thin Baltic Birch with Fiberglass reinforcement?

Postby buttercutter » Fri May 25, 2007 2:36 pm

Making a new lightwind board 145 x 49cm. I've made this before with just 1/2 inch Baltic Birch, and works like a dream in light wind but it's heavy. So we're trying do do one now with 1/4 inch BB Ply and then put layers of glass on top and bottom. Put one layer on top and didn't seem to stiffen it up much. How many layers will it take to get this board strong but still flexy? Anyone ever try this method of thin wood and fiberglass?

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KiteSmurfer
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Postby KiteSmurfer » Tue May 29, 2007 1:38 pm

depends on the weight of glass you using

Also, putting it on the bottom is usually better than the top with Ply - Ply boards break in tension on the bottom usually so this is where the glass is most useful - using the same logic, i assume it would stiffen the board more as well on the bottom.

crabman
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Postby crabman » Tue May 29, 2007 2:28 pm

Trying to make it stiffer by applying more glass will not work . Use two thin pieces of ply with a foam core will work . For awesome flex simply take the core no further than the footstrap inserts.This will give you flex in the tips ,and not between ya feet.

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Postby Phatbob » Wed May 30, 2007 3:16 am

The large plywood board I use now is 1/4in glassed on the bototom with a bit overlapped over the top. It works great! Super flexy! Hasn't broken yet.

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kitezilla
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Postby kitezilla » Wed May 30, 2007 3:30 pm

I have made about 12 different plywood boards, using everything from 1/2 Baltic Birch to 3/8" (my favorite) to 1/4" (adding a second 1/4' piece under the Foot Strap area). I have never fiberglassed any of them. I have a question for those of you who have added glass to the plywood.

Question: Does the fiberglass give the boards a faster REFLEX? That is to say, does the glass not only stiffen the board, but upon flexing the board when turning, does it make the board more QUICKLY SNAP BACK to its original unstressed shape?

The reason I ask this, is that, from my 3 years of experience in using plywood boards, I have concluded that, even though a plywood board may appear to have the same FLEX (ie. "PASSIVE BEND", judged by the standard technique of holding your knee against the board, while it is braced against the floor, and forcing the board to flex, by pulling on the upper end of the board)....even though the flex of the board FEELS the same as the flex of a manufactured board (eg: Spleen or SS Glide), in reality, on the water, the USEFUL flex (performance) of the board is very different. The plywood is inferior to the engineered, layered, foam and composite board, due to its lack of speed in flexing back to shape (reflex).

This enhanced performance of the manufactured board is evidenced by the "livelier" feel of the board in:

(1) Jumps
(2) Turns

Have others, out there, observed and concluded this?

Does the fiberglassing of the plywood blank add any performance characteristic, other than stiffness, durability and weight?

Inquiring minds want to know!

zfennell
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Postby zfennell » Wed May 30, 2007 4:04 pm

kitezilla wrote:Question: Does the fiberglass give the boards a faster REFLEX? That is to say, does the glass not only stiffen the board, but upon flexing the board when turning, does it make the board more QUICKLY SNAP BACK to its original unstressed shape?



compared with plywood, i would say adding glass will give you faster reflex (higher natural frequency)

on a simple level , a board is a spring with a mass .
the stiffer the spring, the quicker the natural frequency (reflex)
the greater the mass, the slower the reflex.

adding minimal glass to top and bottom surfaces would easily increase the stiffness more than the weight ( compared to plywood)

other things to consider for better stiffness/weight (reflex for you)
length of board
thickness of board
thickness profile (where does board actrually bend )
concave vs flat
laminated planks vs plywood ( all the grain is going lengthwise)
lighter wood (cedar, pine, pawlonia, balsa)

you get the idea.
-bill


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