Kaholo and Carbon Fiber Twill Weave.

Has anyone put this on a Kaholo out there?

Why shouldn't I?


7 replies:

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RE: Kaholo and Carbon Fiber Twill Weave.

I haven't built (or even seen live) a Kaholo, but i can't see why not.  Wherever you will put the carbon, I'd skip the undelying layer of 'glass to save weight.  It seems to take a bit more epoxy to fill the weave in the carbon, which may simply be because it's much more difficult to tell when you've actually filled it - the carbon doesn't change color like 'glass so I tended to ere on the side of overfilling. If it was mine, I would lay a thin layer of epoxy on and then lay the carbon on while that layer is wet.  I'd also lay a layer of 4oz 'glass over the carbon at the same time (all wet) then wet out the whole layup.  The 'glass is unnecessary structurally, but if you don't add it, you need to be very careful not to sand into the carbon.  It frays when sanded, and you'd lose the look I assume you want.  The glass over the top will be invisible, and will protect the carbon, which is not forgiving when it comes to abbrasion.  Obviously, my method will be heavier than glass or carbon alone, and all things being equal, 'glass is likely the lightest option (a light carbon layup is tough to acheive without vaccum bagging).  That said, I used carbon all over my boat because it's very strong and looks amazing.

RE: Kaholo and Carbon Fiber Twill Weave.

Disagree about carbon "fraying when sanded". If you need to add glass over the carbon, it seems smartest to skip the carbon. Fair the surface first, do a test sample of your carbon layup on a piece of plastic or glass so you can see if your technique is getting the back wetted, consider applying a sealer coat to the raw wood (and sanding it once dry or applying the carbon after it has kicked but before it has cured), apply your carbon, and then cover with strips of peel ply (nylon sport fabric at the local fabric center works great). You can probably do the whole deck with one piece of peel ply, but you'll need to piece in the rails. (don't know how much of the boat -err, board you want to put carbon on.) Once dry, peel off the peel ply and lightly sand the textured carbon- you'll be sanding the epoxy texture, but there will be some black powder in your sandings, try to avoid that. Unless you're reckless, it won't effect the look or strength of the carbon. Add either another neat coat of epoxy, or your first coat of finish, depending on how you think it looks. TRY a sample 12" square on a piece of scrap ply, from start to finish, you'll see it's not too hard. Whether carbon adds any strength or stiffness to the ply is a different question- I suspect it would be more useful on the inside (tension surface), but then it wouldn't be seen. ;) As I understand it, the exterior sheathing of these boats is primarily for the purpose of adding a hard, impact resistant coating to the relatively soft wood beneath. Glass and carbon are similar in compression, and the hardness of the surface will be dominated by the epoxy matrix anyway, so the choice of fibers is somewhat moot.

RE: Kaholo and Carbon Fiber Twill Weave.

I don't disagree with anything nemochad said here. You just need to be careful with sanding if you don't add the 'glass.  An error would be very difficult to cover asthetically without recovering with additional carbon.  My way is easier but definately heavier and unnecessary structurally.

RE: Kaholo and Carbon Fiber Twill Weave.

I didn't understand this statement:

   "The 'glass is unnecessary structurally....

If you mean that a layer of 'glass over the carbon doesn't have any structural benefit, only an abrasion protection benefit, could you explain why do you think that?

(Here's the reason I ask. When you build a mast with carbon fiber, you are instructed to add two layers of 'glass on the outside.  If, as you say, there is no structural benefit for 'glass layers over the carbon layer, then what is the reason for them in the case of a mast? A mast is never dragged over concrete and rocky beaches, so it doesn't seem that the 'glass could be specified for abrasion resistance.

Intuitively, it seems to me as a layman that the reason is that there's a structural benefit to adding glass layer over the carbon layer.  When a carbon composite component, like a mast in a racing sailboat, fails where wooden masts don't, it is because the carbon part is too stiff, and as a result the stress is too high even for carbon. The carbon masts crack, and the wooden masts bend. When there is a layer of 'glass outside, where strain and stress are concentrated, the stiffness of the member is less, the glass layer soaks up much of the stress, the stress on the carbon layer is reduced, and as a result, the part bends but doesn't break.  The strength of the member in service is therefore higher.

RE: Kaholo and Carbon Fiber Twill Weave.

Glass cloth will see almost no strain at the stress or elongation that will rupture the carbon cloth. If you're using unidirectional fibers (and you're pretty clever), you can use glass for offaxis loads or to bind the carbon fibers. I've heard of using glass for the lengthwise fibers in whippy masts, but not for mast hoop strength. But I'm not a mast designer.


There's a story about supporting a 15 pound bowling ball with a ten pound test piece of elastic, and a 10 pound test piece of string. The elastic sees no load initially, the string is overloaded and breaks, then the elastic stretches and breaks.



RE: Kaholo and Carbon Fiber Twill Weave.

Exactly - A layer of 'glass will add a structural benefit - you just don't need it.  I did not mean to say that it won't be stronger - it's just not necessary in your application.  However, I would view the abrasion restistance (as opposed to shear strength) as a material benefit.

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