VIDEO: Workers Rivet Side Shells during the construction of Liberty ship during World War II.
As useful as pre-assembly was in cutting
production time, the real key to accelerated shipbuilding, however, was
welding. Ships in World War I took longer to build than in World War II
primarily because their hulls were riveted rather than welded. Welding had
been introduced in American ships prior to 1918, although none had an
entirely welded hull. Riveted ships were strong and durable. But riveted
hulls had drawbacks. Chief among these was the time needed to align steel
plates and drill holes for rivets, and to set and drive home the rivets.
To place each rivet (150,000 for a typical hull) took two workers, one on
either side of the plates being fastened. But to reach that point required
the efforts of at least two other workers. A "driller" had to position
each hole in the proper place and drill through the one-inch-thick hull
plate. After the plates were aligned on the frames they seldom matched the
pre-drilled holes precisely, so a "reamer" had to enlarge the holes to
eliminate overlap and allow the rivet to fit. The combined weight of
rivets needed to fasten hull and deck plates could add more than 300 tons
to a ship's hull and subtract that weight from the vessel's payload.
Strong as they were, rivets could pop loose under stress or when hull
plates were damaged. Unless the exterior heads of the rivets were flush
with the hull, they added drag that could slow the ship at sea.