Abstract: An aluminum scaffold tube filled with a predominantly closed-cell foam material selected so as to give the filled tube positive buoyancy in sea water and to resist collapse at pressures of up to at least 14062 Kg/m.sup.2.

Abstract: Drop scaffolding is formed by assemblies of drop tubes 12 and scaffold tubes 15 extending transversely between the drop tubes. Each drop tube has a top coupling secured to an upper part thereof and a bottom coupling secured to a lower part thereof, the two couplings being similar and having cradles with openings directed respectively generally downwardly and generally upwardly. Each coupling comprises an elongate body having a hollow section with a longitudinal axis extending the length of the body, in which section a drop tube is secured. A hook-like cradle 14b, 14c, 14d projects from the body away from the hollow section with an opening x between retaining walls 14c, 14d, each making an acute angle with the longitudinal axis of the section in the quadrant that includes the first end of the body.