US NAVY'S - Incat

Fire Resistance
Aluminium does not burn. There is some loss of strength at
elevated temperatures, where aluminium ranks second
only to steel. However, the majority of shipboard fires are
localised. Because of the high thermal conductivity of
aluminium, a local, brisk fire can occur adjacent to the
hull plating without much increase of metal temperature
and consequent loss of strength. For superstructures,
which are further away from the cooling effects of the
water, fire resistance can be increased by selection of fire
rated materials and floor coverings.
Corrosion
Marine grade aluminium alloys are
highly resistant to corrosion.
Unlike steel, there is no
requirement to paint
the surfaces inside or
out to protect from
salt water, apart, of
course, from underwater
antifouling. There is no dark oxide
“bleeding” through pin holes or cracks
in the paintwork. The 5000 and 6000 series alloys
have shown negligible pitting and loss of strength after
seven year- long immersion tests in salt water. Operation
of the original Incat vessels, now nearing thirty years
old, are also testament to the corrosion resistance of
aluminium vessels.
Welding with Aluminium
The welding of aluminium structures is not new and has
been under constant development for over a century.
Today it is well understood and used by specialised
shipbuilders and equipment manufacturers around the
world. Welding procedures have been developed to
suit very thin materials less than 2 mm thick through to
materials up to 200mm thick. This is not the limit, and
we are sure there will be a need to weld even greater
thicknesses as the size of lightweight ships increase.
The system of pre-fabricating modules and transporting
them to a main ship assembly hall is common shipbuilding
practice but when working with aluminium, particular
attention is needed to allow for distortion and
to minimise the residual stresses in the
final vessel structure. Prefabrication
also improves worker comfort and
safety with welders able to work
upright and at ground level, rather
than having to work above their heads or
be suspended from harnesses or platforms
many metres in the air.
Incat pre-fabrication staff and research and design
teams also develop and build jigs which increase
efficiency enormously.
After consideration of the design factors mentioned
above, it becomes easier to understand why aluminium
high speed vessels are maintaining their position as the
most fuel efficient and safe vessels to service both the
commercial and military markets worldwide.
Postscript: Aluminium and the Falklands Task Force
Of the 100 ships in the British Naval Task Force, nine were sunk. Of these nine, only three, the frigates HMS
Antelope, HMS Ardent and the support ship Sir Galahad had aluminium superstructures. All three vessels had
steel hulls and in each case the damage inflicted suggested these vessels would have sunk regardless of the
material used in the superstructure. In no case did aluminium burn. HMS Sheffield, the first British destroyer sunk
and which was widely reported to have an aluminium superstructure was an all steel ship with both a steel
hull and a steel superstructure.
“There is no evidence that it (aluminium) has contributed to the loss of any vessel.”
As quoted in the Falklands Defence White Paper 14/12/82.
Incat THE Magazine Issue 36 15