Vessels and Ballast Water - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 30

The model is presented in Fig. 17 . More details about the model logic, application
and accuracy of results are presented in David et al. ( 2012 ).
Estimation of Ballast Water Discharges World-Wide
In the past global ballast water discharges were assessed or quoted by, e.g., 10 billion
tonnes by Gollasch ( 1998 ), and 3.5 billion tonnes by Endresen et al. ( 2004 ). At the
time these assessments were conducted, the world seaborne trade amounted to
around 5 billion tonnes of cargo per year, i.e., in 1995 it was 4.651 billion tones,
and in 2000 it was 5.871 billion tonnes (UNCTAD 2006 ). The Endresen et al.
( 2004 ) assessment considered the world seaborne trade to be 8.734 billion tonnes
of cargo, 5.434 billion tonnes in international and 3.3 billion tonnes in national
seaborne trade.
The ballast water capacity varies as a function of the cargo carrying capacity
and ship type, with an average value of 33 % of the vessel's DWT (Suban 2006 ).
However, the ballast capacity is only partially utilized because the vessel's DWT is
commonly not fully exploited. First of all it is necessary to consider the fact that
the ship is not loading the full DWT capacity. From DWT it is necessary to deduct
weight of stores, fuel, fresh water and other weights. This weight usually repre-
sents around 5-10 % of a ship's DWT (Suban et al. 2006 ), hence the ballast water
capacity would be about 37 % of the vessels cargo capacity in terms of weight.
Secondly, vessels frequently do not exploit also their maximum DWT dedicated to
cargo, e.g., different vessels, especially container vessels, car carriers, and general
cargo vessels are usually only partially loaded, and bulk carriers when they load
light cargoes as grains or wood. The BWDA model (see section “ Ballast water
discharge assessment ”) considers all this, hence the estimated discharge would
amount to 33 % of the cargo volume in the world seaborne trade, not considering
the lightweight cargoes.
The world international seaborne trade in 2011 amounted to 8.748 billion tonnes
of cargo (UNCTAD 2012 ), thus the global ballast water discharges from vessels
engaged in the international seaborne trade in 2011 would be about 2.88 billion
tonnes. If we want to estimate the global ballast water discharges for 2013, the
information needed is not yet available, but needs to be estimated. According to the
UNCTAD ( 2012 ) data the world wide economic crisis was refl ected in the decrease
of world seaborne trade especially in 2009, after which it recovered with an annual
growth of about 350 million tonnes per year until 2011, while the average annual
growth from 2000 to 2011 was about 250 million tonnes per year. Assuming an
average annual growth of 300 million tonnes per year as the global economy
recovered after the 2009 crisis and continued to grow (UNCTAD 2012 ), the world
international seaborne trade in 2013 would amount to about 9.35 billion tonnes of
cargo, thus the global ballast water discharges from vessels engaged in the interna-
tional seaborne trade in 2013 would be about 3,1 billion tonnes.
The amounts estimated here are much lower than some earlier estimations men-
tioned above, especially when considering that the global cargo transport today is