Posted by: Ken Smith on March 14, 2005 at 23:35:53:
In Reply to: Re: Rules regarding the use of carbon fiber in DN construction posted by Eric Anderson on March 14, 2005 at 15:26:24:
II make my living analyzing stuff and being critical of other people's work, so be warned.
The wood prices quoted are close to what I've found in the Chicago area, but I'd buy planed 3/4 or smaller for side boards, and the wood suppliers, "Owl Hardwood" for instance, will finish plane it for you. McCormack Lumber has air dried Sitka in Madison, WI, and Aircraft Spruce is the most expensive supplier for spruce I've found. Wicks AIrcraft will supply Sitka spruce cheaper, near St Louis. Aircraft grade may not the best for side boards, as it will be heavier than necessary. You want quarter sawn probably with a more open grain than aircraft grade.
Your cost comparison is very biased to minimizing the estimate of materials for composites. I found the need for a gallon of epoxy for a wood DN hull. I'd expect at least another 1/2 to 1 gallon for the composite side boards. And I cannot find good epoxy at $30/gal. THe price you quote for glass, I do not know how much you anticipate using, so its hard to know if your estimate is good. I shop from USComposites.com for both glass and carbon, and your prices seem much lower than I can find. Wicks Aircraft has about the same prices and less selection than USComposites. You ignore the infrastructure of molds, and vacuum bagging equipment and only consider consumables, an unfair comparison if you do not already have a shop with the compressor, vacuum pump, tubing, manifolds, gages, tables, etc.
Philosophically, composite hulls are not necessary, IMHO. Carbon hulls are illegal. Based on discussions with three people who've built composite hulls (Jeff Kent, Steve Orlebeck, and BJ Johansen) the composite hulls are lots more work. My bet a rule change to allow carbon in hull or plank would fail to make any ballot. These boats are fun because of shop time, as wel as sailing time. Rules changes that threaten shop time for the home builders have always (and always should) be voted down.
Ken Smith