Environmental Engineering Reference
In-Depth Information
to provide for lower air draft.
1
In relation to the fuel and diesel oil consumption dur-
ing a voyage, e.g., a Panamax container vessel consumes approx. 100-180 tonnes of
heavy fuel per day, and according to the
International Convention for the Safety of
Life at Sea
(SOLAS), 1974, vessels need to be adequately trimmed
2
to provide for
optimal hydrodynamics, they need to provide for bridge visibility standards, and for
minimum aft draught for adequate propeller immersion.
Some types of vessels, especially Ro-Ro, container and passenger vessels,
which load cargo or passengers also very high above the waterline, and cargoes
frequently are non-equally distributed, have so called anti-heeling tanks to com-
pensate for transversal unequal distribution of weight and prevent vessel from list-
ing. This is especially important in port during cargo operations. Vessels usually do
not load and discharge water in or from the anti-heeling tanks, but have a constant
volume of water in these tanks which is than being pumped from one side of the
vessel to another.
As a result of these factors, vessels fundamentally rely on ballast water for safe
operations as a function of their design and construction.
Vessel's Ballast System
The number, volume and distribution of ballast tanks are vessel type and size related.
The ballast tanks can be in the vessel's double bottom (DBT - double bottom tanks),
port and starboard along the sides (ST - side tanks or WT - wing tanks), in the bow
(FPT - forepeak tank), in the stern (APT - after peak tank), port and starboard
underneath the main deck (TST - topside tanks or upper wing tanks), and other
(e.g., CT - central tanks). Though FPT and APT tanks are traditional on all types of
vessels, some does not have these tanks, e.g., The Hamburg Express class container-
ships. Some older vessels, mainly tankers, were also using cargo holds (or cargo
tanks respectively) to ballast, but today's vessels have tanks that are dedicated only
for ballasting, i.e., segregated ballast tanks (see Figs.
1
and
2
). The specifi c case
today to ballast in cargo holds may apply to bigger bulk carriers, which may load
water in some of the central cargo holds to sail in so called “heavy ballast condition”
when exposed to heavy sea conditions.
Ballast tanks are connected with the ballast water pump(s) by a ballast water pipe-
line. Water from the vessels surrounding area is loaded on the vessel through the
vessel sea-chest(s) and strainer(s) (see Fig.
3
) via the ballast pipeline to ballast tanks.
Inside the ballast tanks water is loaded and discharged via the ballast water pipe-
line suction head (see Fig.
4
).
Vessels with greater ballast capacity are usually equipped with two ballast pumps
(see Fig.
5
) in order to ensure ballast water operations are carried out even in case
1
i.e., the distance from the water to the highest part of the vessel.
2
i.e., difference between the forward and aft draft, when this exists, means longitudinal list of this
vessel; when there is no trim, vessel is on even keel.
Search WWH ::
Custom Search