Vessels and Ballast Water - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 19

The volumetric ballast water capacity mainly determines the vessels seaworthi-
ness in different static and dynamic conditions. For instance, according to Det
Norske Veritas, Rules for Classifi cation of Ships (Part 3, Ch. 1, Sec. 3) (DNV 2000 ),
ships of 20,000 tonnes DWT and above having the class notation Tanker for Oil and
ships of 30,000 tonnes DWT and above with the class notation Tanker for Oil
Products are required to have segregated ballast tanks. The capacity of segregated
ballast tanks is to be at least such that, in any ballast condition at any part of the
voyage, including the conditions consisting of lightweight plus segregated ballast
only, the ship's draughts and trim can meet each of the following requirements:
The moulded draught amidships (dm) in meters (without taking into account any
ship's deformation) is not to be less than:

dm  20 . 002 . L

( 1 )

where L means length between perpendiculars.
The draughts at the forward and after perpendiculars are to correspond to those
determined by the draught amidships (dm) association with the trim (t) by the stern
of not greater than

t  0 015 . L

( 2 )

In any case the draught at the after perpendicular is not to be less than that which is
necessary to obtain full immersion of the propeller(s) (Perkovi

and David 2002a ).
In general, cargo vessels such as, general cargo, Ro-Ro, e.g., ferries and car
carriers, use only small quantities of ballast water, i.e., generally some 20 % of
their DWT, with some exceptions even of more than 40 % of DWT for special uses
(Capt. Peter Stapleton personal communication). On the other hand, vessels for the
transport of liquid and dry bulk cargoes, e.g., tankers, dry-bulk carriers, require
signifi cantly larger quantities of ballast water, i.e., mostly between 30 and 50 % of
their DWT, what may result to more than 100,000 m 3 of ballast water per vessel.
A summary of the ballast water capacities for main ship types identifi ed by different
authors is presented in the Table 1 (David et al. 2012 ).
The ballast water pumps capacity is mainly related to the speed of vessels cargo
operations, i.e., how much cargo can be loaded or discharged in a certain period of
time, as the ballasting operations are mainly being conducted in the opposite way than
the cargo operations. Some vessels may be loading cargo at much higher speeds than
the others, hence need much faster ballast pumping rates otherwise the cargo opera-
tion may have to be slowed down. Bigger tanker vessels, i.e., crude oil tankers, are the
fastest in cargo loading/discharging rates, nowadays conducting cargo operations at
10,000 tonnes/h or even faster, and bigger bulk carriers with up to 6,000 tonnes/h,
hence having ballast water pumping capacities in the range of 6,000-15,000 m 3 /h.
Container vessels when in most developed ports manage to load or discharge
approx. 18-22 containers 3 per crane per hour (Chief Offi cer Kiril Tereš

č

č enko per-

3 i.e., 40 ft containers or instead of one 40 ft container can be two 20 ft containers loaded or dis-
charged at the same time.