Page 270 - Ship Construction.DJ Eyres 6Ed

Ch22-H8070.fm Page 259 Wednesday, October 18, 2006 6:59 AM
Tanker Construction 259
of the bottom and side shell is inspected. This testing may take place after
the application of protective coatings, provided that welds have been
carefully examined beforehand.
In practice a combination of a structural water test, and air leak test is
often used. The air leak test is carried out on the building berth, the tanks
being subject to an air pressure similar to that required for testing double
bottom tanks. A water pressure test is carried out on one centre tank and two
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wing tanks selected by the surveyors.
Clean water ballast tanks are tested in the same manner as the cargo
tanks, but bunkers and deep tank test requirements are similar to those in
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
dry cargo ships, i.e. a head of water 2.45 m above the crown of the tank is
applied. Any bulkhead not forming a tank boundary is hose tested.

Fore End Structure

Forward of the tank space deep tanks may be fitted. Framing throughout
this space and the forepeak may be transverse, longitudinal, or a combination
of both.
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DEEP TANK If transverse framing is adopted forward floors are fitted at
every frame space in conjunction with a centre line girder or centre line
bulkhead and intercostal side girders not more than three times the trans-
verse frame spacing apart. If longitudinal bulkheads are fitted port and
starboard in the cargo tanks these may be extended to the fore side of the
deep tank in lieu of a centre line bulkhead. Above the floors the transverse
frames are supported by stringers spaced not more than 5 m apart which
are either supported by web frames connected to deep beams to form a
vertical ring frame, or connected to longitudinal stringers on the transverse
bulkheads to form horizontal ring frames. Alternatively, in narrow tanks
perforated flats may be fitted at 5 m spacings.
Longitudinally framed deep tanks are supported by side transverses
five frame spaces apart. Where the depth of the tank exceeds 16 m the side
transverses, also the web frames in a transversely framed tank, either have
one or more deep stringers fitted, cross ties, or perforated flats with deep
beams in way of the transverses or webs.
A longitudinal bulkhead generally must be provided if the tank width
exceeds 50 per cent of the ship’s beam and may solely be a wash bulkhead
on the centre line. Where the breadth of tank exceeds 70 per cent of the
ship’s beam, at least one solid bulkhead on the centre line is recommended.

FOREPEAK A transversely framed forepeak has a similar construction to
that of a conventional cargo ship and includes the usual panting arrange-
ments (see Chapter 20). If the forepeak is longitudinally framed the side