My first instinct was toward composites -- they really do offer tremendous advantages in many ways, mostly their insensibility to water. And you can find I-beams in FRP that are adequate structurally.
http://www.eplastics.com/Plastic/Fiberg ... een-I-Beam
Minimum 6m order, tho. Carbon fiber problematic due to galvanic issues? Would be a good choice if any Ballad has a carbon mast!;)
I use a lot of phenolic countertop material that has acceptable edge strength and terrific face and beam strengths. Thought about building the truss from that. The problem with composites is knowing how good the finished article really is. I guess that's true of welded metals and some imported metals as well. But even at the highest levels of design and fabrication, composites have a tendency to fail unexpectedly, for reasons that are hard to analyze later. Consider the last Volvo Ocean race, when entire hulls were delaminating on the first leg, or the recent Gunboat catamaran that dropped its carbon rig and was abandoned fresh from the factory. Some plastics (like HDPE) begin yielding under loads much lower than their ultimate strength. Others like carbon fiber tend to fail explosively right at their yield strength.
At first, metals had the same learning curve composites are going thru now: boiler explosions, Liberty Ships, etc. These days, metals are such a
known thing, made in large batches in a few factories to exacting standards. If you buy 316L Stainless from an ISO9001 factory, you pretty much know what you are getting. And steel especially is so forgiving. Our poor truss was nothing but rust flakes and lace, yet the mast was still up! OTOH, acetal wouldn't rust in the first place....
There's no one nearby who could make a reliable composite truss for me, and my own skills & knowledge are not good enuf.
Anybody building a truss from composite, please detail it here!
)
Composites are attractive, tho they have strange properties sometimes & carbon fiber also eats aluminum. I bet G10 could be made into an excellent truss: it has a face compression strength around 65k psi, tho I have no idea what its edge strength is. And others here have made very good replacements out of wood, which is a superb material if you can keep it dry. As I mentioned to a fellow with a Ranger 37 who was needing to shim his mast foot, Westsail 32s often used a $3 paving brick under their masts. It is possible to overthink this, and that's a disease I have.
(A sack of concrete mix poured into the cavity might be a pretty good solution! Sink some glue-in studs into it afterwards. Hmmmmm. You'd need to declare your extra ballast to the class measurer, tho.)
