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It
is a well known requirement of the naval architects
the reduction of the ships' top weight, with the
aim of increasing the stability by lowering the
vessel's Centre of Gravity.
For this reason the
attention of the naval architects has been worldwide
looked to the composite materials: recently the
Italian Navy, among the first in the world, has
promoted the adoption of composite superstructures
on a steel-hulled 90 m OPV, the forth of the so
called "Comandanti" Class. Intermarine
has been awarded the contract for the construction
of such large component, having dimensions 38
m in length, 11.5 m wide and approx 8.5 m. height.
The main constraint imposed by the Customer in
designing the composite superstructure has been
the total compliance, in terms of geometry, strength
and rigidity, with the equivalent steel superstructure
built for the first three vessels of the "Comandanti"
Class.
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The results of the Intermarine effort are very
satisfactory: the composite superstructure allows
approx 40% weight saving with respect to the equivalent
steel version.
The superstructure is mainly built with GRP (Glassfibre
Reinforced Plastic), duly integrated, where necessary,
with other structural fibres providing additional
features. The upper part of the fore section (pilothouse
and CIC) encompasses an integrated ballistic protection,
made with alternate layers of glassfibre and kevlar,
offering at the same time structural strength
and protection against the threat of a 7.62 NATO
STD calibre.
Where EMI protection is needed, the composite
structure encompasses a suitable copper net in
function of ground plate for the correct operation
of the antennae: such a solution had been already
successfully implemented and tested in other Intermarine
vessels such as minehunters and Hydro - Oceanographic
vessels.
An additional shielding capability has been obtained
by use of carbon fibre layers in the inner skin
of the superstructure. Carbon fibre contributes
to the overall structural resistance and grants
the correct operation of the electronic equipment,
which results duly protected against electromagnetic
interference (EMI) produced by transmitting antennae
or by other electronic equipment.
"Stealth"
features, although not contractually binding,
have been duly analysed by Intermarine with the
aim to obtain features similar or better than
the steel superstructure.
While the steel structure shows undulation on
the surface, due to the effects of welding, the
composite structure finishing is very smooth,
increasing the benefits of the optimisation of
the geometry. In addition it has to be highlighted
that once reduced RCS (Radar Cross Section) requirements
have to be met, the composite material is more
suitable than steel for incorporating RAM (Radar
Absorbing Materials) features.
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