Page 343 - Practical Ship Design
P. 343
300 Chapter 10
CF in both cases being the minimum specified yield stress in N/mm2.
Whether a change to higher tensile steel brings a reduction in labour cost
depends on how much of the steel used is of a grade and thickness which requires
special heat treatment.
The thinner scantlings used with higher tensile steel means that a structure
constructed in this material inevitably carries a higher fatigue and corrosion risk.
10.5.7 Corrugated construction and swedged stiffeners
The use of corrugated construction for transverse bulkheads provides a good way
of reducing both steel weight and labour costs but this is achieved at the expense of
the cargo capacity unless the cargo is a liquid or a fairly finely divided solid, which
will stow in the corrugations.
The use of swedging to provide the stiffening of steel casings saves both weight
and labour cost but may introduce arrangement complications, whilst fatigue at the
end connections is possible.
10.5.8 Other ways of minimising steel work labour cost
(i) Reducing the number of parts and the complexity of fit-up by paying great
attention to the detail of the design.
(ii) Coordinating the design with the intended production methods to maximise
downhand welding and work done in the assembly shop and minimise
overhead welding and that done on the ship.
(iii) Rationalising plate thicknesses and stiffener sizes used can help to reduce
the steel stock maintained in a shipyard, and possibly reduce buying costs
by increasing bulk buying. It may also simplify construction, but the
advantages are regrettably at the expense of a somewhat higher steel-
weight.
(iv) Taking account of production considerations in the structural design. For
example arranging stringers and girders in a tanker in positions where they
can to act as platforms to aid the fabrication process, rather than positioning
them entirely to minimise steel weight.
10.6 OTHER FACTORS WHICH SHOULD INFLUENCE STRUCTURAL
DESIGN
Apart from structural strength, weight and labour cost, there are a number of other
factors which ought to be considered in well thought out structural design, but
which do not always get as much attention as they deserve:
