Page 341 - Ship Construction.DJ Eyres 6Ed

Ch28-H8070.fm Page 330 Wednesday, October 18, 2006 7:02 AM
330 Ship Construction
might be preferred, but fibreglass can be supported by tongue and grooved
board linings and wood bearers. The thickness of the insulation depends on
the type of material used and the temperature to be maintained in the com-
partment. However the depth of stiffening members often determines the
final depth. Insulating material is retained at the sides by galvanized sheet
steel or aluminium alloy sheet screwed to wood grounds on the frames or
other stiffening members (see Figure 28.3).
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Insulation on the boundaries of oil tanks, e.g. on the tank top above an
oil fuel double bottom tank, has an air space of at least 50mm between the
insulation and steel. If a coating of approved oil-resisting composition with
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a thickness of about 5 mm is applied the air gap may be dispensed with.
Suitable insulated doors are provided to cold rooms in general cargo
ships, and in refrigerated cargo ships the hold and tween hatches may
be insulated. Patent steel covers or pontoon covers may be filled with a
suitable insulating material to prevent heat losses.
A particular problem in insulated spaces is drainage, as ordinary scuppers
would nullify the effects of the insulation. To overcome this problem brine
traps are provided in drains from the tween deck chambers and insulated
holds. The brine in the trap forms an effective seal against ingress of warm
air, and it will not freeze, preventing the drain from removing water from the
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compartment (Figure 28.3).

Refrigerated Container Ships

Many of the container ships operating on trade routes where refrigerated
cargoes were carried in conventional refrigerated cargo liners (‘reefer
ships’) have provision for carrying refrigerated containers and have in many
cases replace the latter.
The ISO containers (usually 20 foot size since with most refrigerated
cargoes 40 foot size would be too heavy) are insulated, and below decks the
end of each hold may be fitted with brine coolers which serve each stack of
containers. Air from the brine coolers is ducted to and from each insulated
container. Connection of each container to the cold air ducts is by means of
an automatic coupling which is remotely controlled and can be engaged
when the container is correctly positioned in the cell guides.
The below decks system described with fully insulated containers means
that heavy insulation of the hold space is unnecessary. On the ships sides,
bulkheads and deckhead about 50 mm of foam insulation with a fire retard-
ent coating may be fitted and the tank top covered with 75 mm of cork and
bitumastic. If provision is only made for the ship to carry a part load of
under deck refrigerated containers these are generally arranged in the
after holds adjacent to the machinery space.