glass/carbon lay-up to stiffen hull?

[Drew W.]

Hey folks
Anyone tried laying some glass or carbon fiber on the inside of the base of their c1's hull to stiffen it? Methods I've heard about (but never seen) involve laying down a layer of 1/8" foam and then a layer or two of glass or carbon over that, but I haven't been able to get any info directly from someone who's done it.

Thanks!
Drew

[Mike W.]

I had a 30 year old wildwater boat that I was scared the strap anchors would pull out chunks of hull if I rolled. I added 3 layers of s-glass to the cockpit area of the hull. The 1st layer was the smallest (covering the saddle, kneepad & strap anchor points), 2nd layer a little larger & the 3rd layer covered everything. This did stiffen that area but the boat eventually broke about half way between the cockpit & bow. They're not supposed to last 30 years anyway.

[Sir Adam]

I would not recommend using Carbon as in inside layer - Carbon is best near the outside as its strong point is tension (I really mean compression here...typing too late ) rather than compression (TENSION) and these days is really difficult to find and very expensive due to high demand in the defense and air line industries). Strenght wise, the same goes for S glass, though many have used s glass (or cheaper E glass to go for thickness which also helps, as you do not need the added abrasion resistence S glass offers on the inside of the boat). Your best bet would be a few layers of Kevlar, or if it�s really floppy a layer of glass followed by a layer or two of kevlar ( which is best under compression (er... TENSION)). Be sure to sand the inside as much as you can so it bonds properly. I would also recommend using West Systems, as it is stiffer than vinyl or poly ester in my experience. (the other two are lighter, however).

You may want to track down Charlie Walbridges boat building manual, and do a few searches here at Cboats for more information on composite characteristics. There are many folks that post here much more knowlegable than I am on the subject of boat building and composites....

[John Coraor]

Adam:

You placement advice may be sound, but I believe that the rationale for that advice is backwards, at least as far as kevlar is concerned. Kevlar is usually recommended as the innermost layer because it is strong under tension, not compression. When an outside force is exerted on kevlar (e.g. from a boat hitting a rock, or from kevlar body armor being struck by a bullet), the innermost layers are placed under tension as the foreign intrusion deforms the boat/vest inward, stretching the innermost fibers.

John

[Sir Adam]

Your right John...I flipped compressive and tension stresses in the description-I am over in Switzerland right now visiting NZMatt, and arrive last night before typing that missive....

Time to get back to vacation:)

[John Coraor]

Drew:

I've used strips of thin foam in the middle of a layup to create "ribs" to stiffen a composite hull, but always in the course of the initial layup, never as a later add-on when adhesion is more of an issue. I would be a little leary of adding on a really large "pad" of foam because of the possibility that adhesion problems would cause delamination over such a large area. However, not having tried it before, I'll happily defer to someone who's used this technique with success.

I have also added carbon fiber "ribs" on the interior of a hull after the layup is complete. You could probably use the same technique on a used boat whose interior has been sanded thoroughly. These were made by pre-wetting the hull where each rib is to be laid up, placing a rib of unidirectional carbon fibers about 1 - 1.5 in. wide, and then concentrating the fibers into a much narrower strip with your brush in the course of wetting them out. This rib is then covered with a length of wet-out seam tape to secure it. I got the unidirectional carbon fiber from John Sweet years ago. Sweet Composites lists what sounds like a similar product on their web site (ask Davey if it would work for this application).

Certainly, Adam's advice to use West Systems is generally best for any later modification of an existing composite layup as epoxy has better adhesion to an existing layup than polyester and, to a lesser extent, vinylester.

John

[Drew W.]

Thanks for the responses all!
I forgot to mention one very important thing, this would be on the inside of a plastic boat (Large Flirt) instead of a composite boat (my bad, sorry!). If I remember right, the thin foam layer was to make it so that a crease wouldn't form at the edge of the glass or carbon lay-up (that could happen if carbon or glass were right against the inside of the plastic because the plastic isn't nearly as rigid?) In light of that, anyone have any suggestions? Thanks!

[PAC]

you could think about strips of glass or aluminum that is glassed over. But best would be plastic.
If you have access to an old beater plastic boat .. cut it up and weld the plastic.
Or (BEST) just do a modified TEAM etc Conversion set up. I think Mike W. has a sheet he was looking to shead.
It's just a thin sheet of plastic that you work into the boat using a heat gun that will have you banging rocks in no time.
Search on Team etc or outfitting for details.
Paul C.