Page 238 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

11.6.4 Loading Segregated Ballast
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In general, there are no restrictions on ballasting Segregated Ballast
Tanks (SBT) during the cargo discharge operation. However, the following
considerations should be taken into account:
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
Ballast should be taken as necessary to meet air draught requirements
on the berth, particularly when hard cargo arms are connected.
Ballast should not be loaded if it may cause the ship to exceed the
maximum safe draught for the berth.
Loading of ballast should not cause extreme shear forces or bending
moments on the ship.
Care should be taken to ensure that excessive free surface is not
allowed to occur as this may result in the ship assuming an angle of
loll, thereby jeopardising the integrity of the loading arms. This is
particularly relevant to double hull tankers (see also Section 11.2).

11.6.5 Deballasting in Port

11.6.5.1 Oil Content Monitoring

The use of an oil content monitor for monitoring the discharge of
clean or segregated ballast will give an early warning of any
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undiscovered contaminated ballast caused by, for example,
inter-tank leakage when loading and deballasting are being
carried out simultaneously.

11.6.5.2 Deballasting of a Ship Fitted with an Inert Gas
System

Ships fitted with an inert gas system must replace the ballast
discharged from cargo tanks with inert gas, so as to maintain the
oxygen content of the tank atmosphere at not more than 8% by
volume.

11.6.6 Discharging Segregated Ballast
To avoid pollution due to contaminated segregated ballast, the surface of
the ballast should be sighted, where possible, prior to commencing
deballasting. When segregated ballast is being discharged, it is prudent to
monitor the ballast being discharged over board by means of a ballast
water monitor. This may give the earliest warning of any inter-tank
leakage between cargo and ballast tanks that may have been undetected,
or even have been undetectable, before starting the ballast operation. As
an additional precaution, on commencement of deballasting, a visual
watch should be established to observe the ballast as it discharges into
the sea. The operation should be stopped immediately in the event of
contamination being observed.

11.6.6.1 Air Draught Management
Ballast carried in segregated tanks may be retained on board in
order to reduce the freeboard. This may be necessary because of
weather conditions or to keep within the restrictions of the
terminal metal loading arms or shore gangway for example. Care
must be taken, however, not to exceed the maximum draught for

204 © ICS/OCIMF/IAPH 2006