Carbon Fiber for Hull Exterior?

[Shudoman]

I noticed that the CLC site is selling 5.7 oz carbon fiber for a reasonable price. I was wondering if anyone (John?) had any thoughts on using carbon fiber for laying up the hull exterior instead of the 6oz fiberglass?

My thoughts are that that carbon fiber would give a much more rigid and abrasion resistant bottom.

Aside from the cost what would be the down side of going this way? Would the layup be any harder than doing it in fiberglass. After completing the interior fiberglassing of my PocketShip I've gotten pretty good at fiberglassing.

Thanks,

Bill

[John C. Harris]

While I'd love to take your money for all that carbon fiber, I'm going to urge you not to do it.

Good things about carbon fiber in general:

1. For its weight, carbon fiber is simply astonishingly strong.
2. Carbon fiber has a certain coolness cachet. Lamborghini offers a $8,950 carbon fiber "look" interior package. At CLC we use it decoratively from time to time.
3. It's just the thing for helicopter blades, race car bodies, Boeing 787 wings, racing yacht masts, and tennis rackets.
4. Struggling here for anything else.

Bad things about carbon fiber in this context:

1. It is chokingly expensive, even when CLC bumbles onto a pallet of affordable quality fabric.
2. While a carbon-sheathed PocketShip would be a lot stiffer torsionally, it would not be lighter. I'm a pretty competent composites guy but I'm STILL not good enough to create carbon layups that are any lighter than the equivalent E-glass layup without resorting to vacuum bagging and peel ply.
3. PocketShip is already exceptionally stiff because of the "eggcrate" plywood construction and the fiberglass inside and out. Say the stock boat is at 400% of desired strength; maybe going to carbon fiber takes it to 700% or 800%. Why? Maybe if you're parachute-launching out the back of a C-130. (Which would be a nice way to go explore places like the Maldives in a small boat.)
4. Carbon sucks to work with. Very tricky to "wet out" properly (see #2), and the graphite dust is especially toxic when sanded.
5. Carbon fiber is heroically strong but very brittle. It will do poorly with the impact loads on the outside of the hull of the kind small boats endure: whacking the corner of a dock, hitting driftwood, etc. (Because carbon is so much stronger in tension, if the goal was an aerospace-spec PocketShip, vacuum-bagging carbon onto the interior surfaces of the hull would be better, sticking with e-glass on the outside.)

I'd like to sail a PocketShip with a hollow carbon mast, boom, and yard. It would be noticeably stiffer and faster under sail. But making such spars yourself requires sophisticated skills; buying them would cost thousands of dollars.

So, carbon fiber is a bust for PocketShip.

[Shudoman]

Thanks John,

That's just the advice that I needed!

Bill