2.10 Where Ballast Water Exchange at sea is the
chosen method, the overall design strength and stability of the ship
should be sufficient to permit its execution on all ballast voyages
and in all except severe weather conditions. For the guidance of the
master, the maximum sea state and swell conditions identified by the
builder, if any, in which ballast water exchange can safely be carried
out should be recorded in the Ballast Water Management Plan.
2.11 The design of the ship should make it easy
to achieve exchange at sea, by reducing the demands upon other crew
resources. In particular it should endeavour to minimize:
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.1 the number of operational steps;
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.2 the time taken, and
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.3 the number of partially loaded tanks and the
duration of their partial loading, needed to complete a ballast water
exchange sequence.
2.12 The design of the ship should include consideration
of the consequences of ballast water exchange at sea including: stability,
hull girder strength, shear forces, resonance, sloshing, stemming,
propeller immersion, limitations brought about by insufficient strength
in various parts of the ship when the tanks are sequentially emptied
and appropriate strengthening incorporated to allow this operation
to be conducted safely.
2.13 Where the sequential method of exchange is
to be used, particular attention should be given to the ballast tank
layout, total ballast capacity, individual tank configuration and
hull girder strength. If the Plan requires simultaneously emptying
and refilling closely matched diagonal tanks then consequential torsional
stresses should be considered. Still water bending moments, shear
forces and stability should remain at or within safe limits.
2.14 Where the flow-through method of exchange
is to be used adequate provision should be made to avoid the risk
of over pressurization of ballast tanks or ballast piping. Enhancements
in this regard may include the installation of additional air pipes,
installation of tanker hatches (as an alternative to deck manholes),
internal overflow pipes (to avoid water flowing over the deck) and
interconnecting ballast trunks between tanks where applicable and
possible.
2.15 Where the dilution method of exchange is
to be used adequate provision should be made for appropriate piping
arrangements to facilitate the loading of ballast water and, simultaneously,
the unloading of the ballast water at the same flow rate. The hydrodynamic
performance of the ballast tank is crucial to ensure full water exchange
and sediment scouring.