Im about to make my third plywood kiteboard. By previous 2 boards have been made out of a single peice of 12mm ply that i bent by soakin in water, which is a pretty hit or miss method. Am now looking to make a board by gluing 2 peices of 6mm together and using a rocker table to get the right rocker.

I was just wondering if there are any real advantages in making ply boards hollow rather than just gluing the deck peice and the bottom peice directly together.

Also what is the best rail shape to use, do i want sharp rails or rounded rails like on a surf board?

One more thing, what gives better upwind ability, a squarish board or a more elliptical shape. And which is better for waves (where i do most of my riding).

forgot, one more thing, what is better constant or a 3 stage rocker?

You can reduce weight, without reducing 'floatability'.
Strength is not really a problem. and you can always reinforce with some glassfibers and polyester or resin.



Squarish is good for upwind, elliptical for waveriding.

It might be difficult to build a hollow board from 2 pieces of plywood. I usually use 3 pieces of 3.6mm plywood and cut out the middle one like is shown on this site: http://www.stuntkites.nl (--> kiteboards --> servaas 13 --> bottom of the page).

with 3 layers You get the desired rocker much easier than with 2 layers

A 3 stage rocker gets you going faster because of the bigger contact surface in the middle of the board but it doesn't make that big of a difference. If you want a board that planes early, you should just make it a bit wider.
That's just my two cents, feel free to correct

With a hollow board made of 3 layers of ply do you need any glassfibre reinforcement??

You don't need rocker if you let the board have some flex. Flex will give you "dynamic rocker" and a flater board will give you better light wind performance as well. My favorite board has no rocker at all.

Chris