How much carbon?

[SaulOhio]

I am working on my own hydrofoil. The wings themselves are done, and I have built a few versions of the vertical strut. But I am thinking of building a new one that will turn out hollow. I have a mold made by a CNC machine out of artificial plastic wood. I plan on laying up a lot of carbon clot on both sides of the mold, adding a couple of those long balloons used to make balloon animals with tubes leading outside the mold, then vacuum bagging the mold to suck out as much resin as possible. The balloons should inflate, pushing out more resin.

How much carbon fiber should I be using? How would I calculate such a thing?

BTW, would epoxy resin degrade the latex of the balloons?

[rynhardt]

I'm no expert on masts, but I've built some carbon beams in a mould, Approx 1.4m long and 50cm dia. Foam core, carbon skin.

Why go for a hollow core? You need some kind of internal structure for compressive and shear support, and building some kind of trellis or internal beam or bracing will be fiendishly difficult.

If you want light and strong, the foam sandwich is hard to beat.

as for how much carbon.. gut feel says 300gsm uni and 150gsm triax should be a good start. If that breaks, go heavier.

[Blackrat]

you wasting your time if you want decent performance

you must have a core , and even better a shear web

you will need atleast 2x400 uni and 2x400 biax on a core

my latest mast flexes 10mm on the flex test (5kgs at 800mm)

[Johnny Rotten]

I am working on my own hydrofoil. The wings themselves are done, and I have built a few versions of the vertical strut. But I am thinking of building a new one that will turn out hollow. I have a mold made by a CNC machine out of artificial plastic wood. I plan on laying up a lot of carbon clot on both sides of the mold, adding a couple of those long balloons used to make balloon animals with tubes leading outside the mold, then vacuum bagging the mold to suck out as much resin as possible. The balloons should inflate, pushing out more resin.

How much carbon fiber should I be using? How would I calculate such a thing?

BTW, would epoxy resin degrade the latex of the balloons?

Ballooons don't work too well as bladder as they are difficult to inflate into a pile of sticky goo and expand without getting stuck in said goo. As a result they don't expand well and put uneven pressure on the inner cavity, and yield crap results. unless they are perfectly fit to the mold.

If you REALLY wanna go this route, just for the challenge.
(which I wouldn't recommend due to reasons others mentioned. check out the following)

http://vimeo.com/35648020
http://vimeo.com/37883424
would still likely have unique challenges on something less round like as a mast....but you could do it

Regarding how much carbon to use, depends on thickness of the mast and desired stiffness more than anything.

how to calculate it,
Without getting into a lesson on structural mechanics Start googling bending stiffness and moment of intertia. If the math looks too heavy, you're probably outta your league. (engineering stuff) but not terribly complicated. If you get it with ease but want some clarification I can help clear up any questions in PM