On Sun, 13 Jan 2008 08:56:00 -0800, Alan Gomes wrote:

Cal used a mild steel beam that runs athwartships to support the
compression of the mast.

Steel is cheaper than corrosion proof aluminum, which, contrary to
popular belief, is no lighter. The strength to weight of mild steel
and common aluminum alloys is about the same. Aluminum would be
bulkier, which means possibly stiffer. Of course, maybe you design for
stiffness, and let strength take care of itself. Houses are that way:
they hardly ever fall down, but quite a few are not quite stiff
enough, and when the wind blows, the plaster cracks.

Casady