Protection of Fuel Tanks Safety ahead! - GL Group

COVER STORY | FUEL TANK PROTECTION
Fig. 1 Fig. 2
Generally, the tanks should be located as far inboard
as possible in order to avoid large outflow in the case of
lateral damage. Fuel tanks located directly on the double
bottom should be oriented to minimize the minimum oil
outflow factor, i.e. inboard of B/5. Regarding the vertical location,
the bottom damage contribution can be eliminated
by placing the tanks above the waterline, i.e. at 30% of the
overall depth of the vessel.
The ideal fuel tank arrangements depend on the type of
the vessel. For bulk carriers, one possible solution consists
in locating the fuel tanks in the topside tanks, protected by
a void space. The topside tanks are adjacent compartments
extending along most of the vessel’s length, allowing easy
installation of continuous piping and heating systems.
A Partial Triple Bottom
On tankers, some of the fuel could be carried within the
engine room in tanks away from the outer shell. In some
instances, the cofferdam in front of the engine room could
also be utilized for storing fuel.
For container vessels, one possible solution is to construct
a ‘triple bottom’, placing the fuel tank above the water
ballast tank inside the double bottom. It is also possible
PROTECTION OF FUEL TANKS: THE NEW IMO REGULATION FEATURES TWO APPROACHES
Descriptive Requirement
According to the descriptive requirement of the regulation,
fuel oil tanks must be located above B/20, or at least
0.76 m from the bottom, whichever is greater, not to exceed
2.0 m. This is in line with new the SOLAS (SOLAS 2009 MSC
80/24/Add. 1, June 2005) requirements so as to avoid subjecting
vessels to different minimum double bottom height
requirements resulting from different IMO conventions.
Prevent Pollution. The calculation of the required wing
tank widths or minimum distances from the outer shell accounts
for the total fuel oil capacity. Widths range from 1 m
(0.76 for tanks smaller than 500 m³ on vessels with a capacity
below 5000 m³) to 2.0 m. Furthermore, the regulation
includes provisions to prevent pollution from oil pipes.
Application of MARPOL Annex I Reg. 12 A:
Fuel oil capacity:
Total aggregate fuel capacity C>_ 600 m 3
Exception: individual tank capacity < 30 m 3
Small tanks aggregate capacity < 600 m 3
Maximum individual tank capacity 2500 m 3
Fuel oil type:
Heavy fuel oil, marine diesel oil, gas oil
14 nonstop 4/2006
For bulk carriers, one possible solution is locating
the fuel tanks in the top side tanks protected by a
void space (Fig. 1). For container vessels, a possible
solution is to construct a ´Triple bottom`, to place the
fuel tank above the water ballast tank in the double
bottom (Fig. 2). Figures 3 to 5 show more possible
cross-sections of a container vessel.
HFO – Heavy Fuel Oil WB – Water Balast
MDO – Marine Diesel Oil
SHIPBUILDING. The Design must consider the new
IMO regulations for fuel tank protection.
to construct a partial “triple bottom” that does not extend
across the entire hold area. The tanks in the turn of the bilge
usually have recesses to provide a foundation on which to
place the containers. They can be designed to assure the
continuity of the double hull between wing and bottom
Probabilistic Requirement
The probabilistic approach within the regulation can
be used as an alternative to the descriptive parts of the
regulation regarding double bottom heights and wing tank
widths. The alternative requirement is based on a probabilistic
concept of non-dimensional oil outfl ow, comprising
outfl ow calculations for side and bottom damages. This
method was validated by extensive analyses of vessels
complying with the requirements of the deterministic
approach of the regulation. The mean oil outfl ow is determined
irrespective of whether the damage is a side or a
bottom damage and is combined into a non-dimensional
computational parameter OM.
More variety. When regarding grounding damages, the
initial grounding, the deceleration and subsequent effects
from currents, tide and waves are all taken into consideration
when the oil outfl ow. A number of scientifi c research
studies were undertaken to evaluate the particular effects.
In summary, this approach accounts for a larger
number of aspects in a more refi ned way, allowing fuel
tanks to be arranged more fl exibily to accommodate special
needs.However, more optimization work is obviously
required.