Posted by: Eric Anderson on March 14, 2005 at 15:26:24:
In Reply to: Re: Rules regarding the use of carbon fiber in DN construction posted by Paul Goodwin on March 14, 2005 at 08:36:54:
I am not sure I would agree that it is much more expensive to build out of balsa/ glass then conventional lumber. Maybe you have access to much cheaper high quality lumber than I can find.
Side board costs assuming I start with 4/4 stock rough and joint and plane it myself. Costs from looking around at New England Lumber mills
Basswood 54 $
Western Read Cedar 104$
Clear spruce 171$
Aircraft grade Sitka Spruce 348$ from aircraft spruce
Cost to build end grain balsa sideboards:
Balsa bought by Box 35$ You do have to buy 5 boats worth at a time.
Biaxial Glass 24$
Unidirectional S glass 67$
Epoxy/ vacuum
bagging expendables 20$
Totals ~150$ Hull
Labor to build 2 sideboards in mold~ 5 hours Any additional labor in this method is more then used up sorting through lumber yards trying to find other lumber.
Cost savings to build using unidirectional carbon in place of unidirectional S Glass 26$
Sideboard costs~ 125$ per hull
Everyone is still limited by a minimum weight of 46 lbs. My argument for this type of construction is that it should be more repeatable, and more robust.
As far as balsa/ carbon planks go, they make no sense. It would be way too light. Even spruce/glass planks are at minimum weight. Personally I am building my new planks Ash/basswood/ash with S glass Uni to stiffen them up. I am looking for about 200 lbs/inch deflection. I would prefer to stiffen them with carbon Uni because you need a lot less of it and it is cheaper. Do I think stiffening it with carbon is faster then stiffening it with S glass? Nope, but it is easier. As far as shape and drag go. You can duplicate any shape that a CNC uses if you have the time and patience. A CNC just lets you build it faster. I was indicating state of the art from a manufacturing point of view, not necessarily from a performance standpoint.
I can’t see any reason that allowing carbon in construction would make a boat faster unless the minimum component weight was lowered. There is no agreement as to what the optimal dimensions of a DN are. There is also no agreement as to how stiff or flexible a hull or plank should be. What characteristic could changing from S glass to a carbon composite impart to boat has that you can’t duplicate in wood?
Personally, I would argue that composite construction is no harder then all wood construction. Runners today are Composite construction. No one argues about that. They are easy to build at home.
If there is a valid reason why carbon reinforcing in the hulls, or planks or booms will lead to a faster boat, I would like to hear it. I honestly can’t think of why it should. I do think it makes my life easier as a home builder to be able to use it.
Eric Anderson US 5193