Question.
State, with reasons, the locality and extent
of damage which may be sustained by the hull structure of a ship being driven
hard through heavy seas.
Describe how such damage stated in (a) can
be made good.
Answer.
Most likely to be damaged are:
Pounding region
This is the bottom shell for the forward 0.25 of the
length of the vessel, three strakes of plating either side of the keel. This
region is subject to severe impact stress.
Panting region
This is the forward 0.15 of the length of the vessel,
but especially the forward 5% to 71\2% of the length (i.e. forward of the
collision bulkhead). The panting stresses are cyclic and arise due to the
fluctuations in water pressure as the forward end immerses/emerges during
pitching.
At end connections/discontinuities
There is a susceptibility to cracking and failure at
end connections and other discontinuities due to the stress concentrations that
arise.
Damage may
be made good as follows:
Pounding region
Any indented shell plating/frames should be 'faired'
back to shape if possible (using wedges, shores, strong backs and heat if
necessary). If this is too difficult, replace the bottom shell longitudinal
grinders and floors as required.
Panting region
The same procedure as
with pounding damage should
be followed. Repair/replace
shell plates, frames, stringers and panting beams as required.
At end connections/discontinuities
•Gouge or grind aft end connection welding and
re-weld.
Drill the ends of cracks, gouge and weld if safe to do
so.
If watertight integrity is threatened
can use a cement box as a temporary repair.