Page 272 - Ship Construction.DJ Eyres 6Ed

Ch22-H8070.fm Page 261 Wednesday, October 18, 2006 6:59 AM
Tanker Construction 261
houses. Particular attention must be paid to any endings in the midship
length of the hull. As the machinery is aft the poop front merits special
attention, and is in fact structurally similar to the bridge front, since its
integrity is essential.
A particular feature of the tanker with its lower freeboard is the require-
ment for an access gangway at the level of the first tier of superstructure
between accommodation spaces. This is still often found on vessels with all
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accommodation aft, although the regulations would permit a rail or similar
safety arrangement at the deck level. The provision of a gangway in the
latter case is at the owner’s wish, and is an added safety factor at greater
and FSU in a single floating unit. ศูนย์ฝกพาณิชย์นาวี
initial cost, requiring additional maintenance. Another feature is the absence
of bulwarks on the main decks, the regulations requiring the provision of
open rails over at least half the length of the wells, which are often awash
in heavy weather.

Floating Production, Storage and Offloading Vessels

Floating production, storage and offloading vessels (FPSOs) and Floating
storage units (FSUs) are now a common feature of offshore oil installations.
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A typical FSU is of 100 000 tons deadweight with a storage capacity of
112 000 cubic metres representing 10 days production. Crude oil from a
floating production unit (FPU) is transferred to the FSU where it is loaded
via a submerged turret loading (STL) system. From the FSU the crude oil is
transferred to shore by shuttle tankers, which are loaded by flexible hoses
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from the stern of the FSU. An FPSO combines the functions of the FPU
Many oil tankers have been converted to FPSOs and FSUs but there is
an increasing trend to new design and build contracts for such vessels. The
basic hull construction is similar to that for conventional tankers but there
are arrangements and structural features peculiar to these vessels. The
vessels are moored using a turret system forward which allows the hull to
weathervane into the wind and waves to reduce dynamic loading on the hull
girder. However, because the waves will be coming mainly towards the bow
for the whole of its life the hull girder will experience greater fatigue problems
than would be the case for a conventional tanker. The conventional tanker
carries little in the way of loading on its main deck whereas an FPSO is fit-
ted with a substantial oil production facility, which can weigh in excess of
20 000 tons. This loading needs to be transferred into the hull structure
which means that vertical structural components are more complex and
substantial than those of a tanker. Further, because both FSUs and FPSOs
are expected to remain on station for their lifetime and withstand arduous
conditions without drydocking, the exposed hull construction is generally
upgraded and strengthened with increased corrosion protection.