Page 59 - Ship Construction.DJ Eyres 6Ed

Ch05-H8070.fm Page 48 Wednesday, October 18, 2006 8:02 AM
48 Ship Construction
A proprietary steel sandwich plate system (SPS) has been developed
which consists of an elastomer core between steel face plates. Elastomers
are a specific class of polyurethane that has a high tolerance to mechanical
stress i.e. it rapidly recovers from deformation. The SPS elastomer also has
a high resistance to most common chemical species. Initial application of
SPS in shipbuilding has been in passenger ship superstructures where the
absence of stiffening has increased the space available and provided factory
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finished surfaces with built in vibration damping, acoustic insulation and
fire protection. SPS structures have been approved with an A 60 fire-resis-
tance rating (see Chapter 27). Also SPS overlays have been applied to
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
repair existing work deck areas. SPS structures can be fabricated using join-
ing technologies presently used in the shipbuilding industry, but the design
of all joints must take into account the structural and material characteris-
tics of the metal-elastomer composite. The manufacturer envisages the use
of SPS panels throughout the hull and superstructure of ships providing a
simpler construction with greater carrying capacity and less corrosion,
maintenance and inspection. In association with the manufacturer Lloyds
Register in early 2006 published provisional Rules for the use of this sand-
wich plate system for new construction and ship repair. The Rules cover
construction procedures, scantling determination for primary supporting
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structures, framing arrangements and methods of scantling determination
for steel sandwich panels.
The Norwegian classification society, Det Norske Veritas (DNV), have
proposed for bulk carrier hulls the use of a lightweight concrete/steel sand-
wich. They envisage a steel/concrete/steel composite structure for the cargo
hold area of say 600 mm width for the side shell but somewhat greater
width for the double bottom area. This sandwich would be much narrower
than for a comparable steel-only double skin bulk carrier thus increasing
the potential carrying capacity although water ballast may have to be car-
ried in some designated holds as the double skin would not be available for
this purpose. DNV consider the other advantages of the concrete/steel
sandwich to be reduced stress concentrations with less cracking in critical
areas, considerable elimination of corrosion and elimination of local buck-
ling. At the time of writing DNV were undertaking a two-year investigation
programme in association with a shipyard to study the practicalities of their
sandwich proposal.

Steel Castings

Molten steel produced by the open hearth, electric furnace, or oxygen
process is pored into a carefully constructed mould and allowed to solidify
to the shape required. After removal from the mould a heat treatment is
required, for example annealing, or normalizing and tempering to reduce