Notes on Torsional Stress on ships

When a body is subject to a
twisting moment which is commonly referred to as torque, that body is said to
be in ‘torsion’. A ship heading obliquely (45°) to a wave will be subjected to
righting moments of opposite direction at its ends twisting the hull and
putting it in ‘torsion’.
In most ships, these
torsional moments and stresses are negligible but in ships with extremely wide
and long deck openings they are significant. A particular example is the larger
container ship where at the topsides a heavy torsion box girder structure
including the upper deck is provided to accommodate the torsional stresses.
Torsional stresses also
occur due to unsymmetrical loading along the centre line of the vessel. (For
example, too much load on the fwd-port side and at the aft-stbd side)