After completing this chapter the learner will be familiar with the
configuration of a typical ship's fuel storage arrangement be familiar with the
configuration of a typical ship's fuel transfer system know the problems
associated with storage of fuel onboard ship
as we will see later in the module the actual fuel storage and transfer system
for any individual ship would be dictated by the type of machinery fitted
the trading pattern and the trading area amongst other things in this section we
will look at some typical common arrangements for handling fuel onboard
ship but you should always make yourself familiar with the actual systems onboard
your ship if you are involved in bunkering or fuel transfer operations
recent amendments to MARPOL annex one which came into force in August 2007
have introduced a requirement for all ships with a total fuel capacity of more
than 600 cubic meters delivered after the 1st of august 2010 to have fuel
tanks located inside of the double hull structure this effectively means all
ships ordered from the date the amendment came into force the amendment
also limits the maximum capacity of a single tank to 2,500 cubic meters the
purpose of this is to limit the pollution potential of these ships in
the event of a grounding or collision incident traditionally fuel storage
tanks have been referred to by names related to the position of the tank
within the ship's structure the list gives some common examples the
introduction of the recent Marple amendments regarding double hull
requirements for new vessels mean that the fuel tanks will have to be contained
inside the inner hull for new vessels the traditional names no longer describe
the tanks accurately double bottom and wing tanks will no longer exist as such
many vessels have already adopted a simple system numbering the fuel tanks
from forward and identifying them by port and starboard location there are
many different arrangements for onboard fuel storage and the example used in
this module is a typical general arrangement remember you should always
familiarize yourself with the actual arrangement onboard the vessel you are
sailing on when planning the fuel storage arrangements the ship designer
needs to consider a number of factors we have already stated the main factors
which are the type of machinery fitted and the fuel types required the trading
pattern and the trading area consideration must also be given to
segregation of different fuel grades and to the
effect on the ship's list trim and stability of using fuel during a voyage
you will appreciate that it would be no use having a single tank for all of the
fuel or having all of the fuel tanks arranged down one side of the ship the
storage tank positions are also selected to minimize the risk of pollution in the
event of collision and to minimize fire risk
the recent Marple amendment mentioned earlier is an example of this with the
need for double hull arrangements on new ships it is not permitted to use either
the forepeak or after peak tanks for fuel storage a fuel tank requires
certain fittings in order that the fuel system is safe and meets the vessels
requirements for storage and transfer of the fuel the items given in the list
should be considered as the minimum requirement for fuel tank fittings other
fittings which you may find fitted to the fuel tanks on the vessels you sail
on may include remote reading content gauges heating coils and temperature and
level alarms the exact specification will depend on which classification
society the vessel is classify as well as any flag state requirements all fuel
tanks must have an air vent arrangement to avoid the risk of overpressure or
partial vacuum occurring in the tank the arrangement should allow the air to exit
when filling the tank and enter when taking fuel from the tank the vent pipe
should have a diameter 25 percent greater than the filling line the vents
should be positioned in an area where there is minimum risk of ignition of any
vapors exiting the vent as a further safeguard a flame screen normally a wire
mesh should be fitted to the outlet of the vent since the vents are normally
positioned on an open weather deck there is a risk of water entering the tank
through the vent during rough weather to prevent this happening the vent head
will have a valve fitted usually either a ball or a disc type float valve during
normal conditions the float will remain in its lower position if the deck area
in the vicinity of the vent becomes flooded the float will rise onto the
seat closing off the vent pipe you should be familiar with the vent
arrangements for your vessel and the maintenance requirements for correct
operation when the fuel is on board it will contain impurities such
as dirt and water in time these will settle out in the bottom of the tank
forming a residue of sludge it is necessary to manually clean the tanks
regularly to remove the sludge to prevent too much accumulating in order
to do this the tank must be provided with a manhole door to allow access if
you are involved in cleaning fuel tanks you must observe all of the requirements
for entering and working in an enclosed space these requirements are shown in
the list make sure you are familiar with the requirements for tank entry on each
Bethel you sail on in the event of a fire the fuel tank suction valves need
to be closed to prevent the contents of the tank feeding the fire whenever the
fuel tank suction valves are in the same space as the machinery that they are
supplying it is necessary to have remote operated
quick closing valves fitted this ensures that the valves can be closed even if
the fire is in that machinery space the quick closing mechanism must be of an
approved type they can be operated by various means pull wires hydraulic and
pneumatic actuators or solenoid valves are commonly used controls for all of
the remote closing valves as well as ventilation fan and pump emergency stops
are usually placed in a common emergency station the valves and stops should be
tested regularly to ensure correct function and you should make sure that
you were aware of the operating procedures on your vessel most ships
fuel tanks are fitted with sounding pipes
although classification societies do allow alternate arrangements as long as
they are of an approved type sight glasses and direct reading contents
gauges may be used instead of sounding pipe arrangements but they must have
automatic closing devices to avoid spillage in the event of failure this is
usually achieved by fitting spring-loaded self-closing coughs at the
tank connection we're sounding arrangements are used the classification
society rules give preferred positions for the sounding pipes for sounding
pipes which are positioned in the engine room the rules require that they are
fitted with self closing coughs usually of the gravity closed type
the sounding pipe must also be fitted with the test cock positioned below the
self closing cock so that you can check for a high level before opening the self
closing cock there are other fittings commonly found on fuel tanks and these
may include fuel storage tanks should be fitted with high level alarms to prevent
overfilling unless an overflow arrangement is provided low level alarms
are also sometimes fitted to avoid running transfer pumps dry settling
tanks and service tanks are always fitted with low level alarms on vessels
classed for UMS operation a heating facility has to be provided for all
tanks used for heavy fuel oil usually in the form of steam or thermal oil heating
coils high temperature alarms may be fitted to fuel tanks to warn against
high temperature of the fuel where the heating medium temperature can exceed
220 degrees Celsius a high temperature alarm must be fitted a temperature
indicator should be fitted to all tanks that can be heated there is no point
filling the fuel storage tanks if the fuel cannot be transferred to where it
is to be used a suitable transfer system which will allow transfer of fuel from
any location to the settling tanks is required the system should have at least
two transfer pumps each of which is capable of transferring fuel at a
greater rate than the maximum consumption rate of the machinery
installation suction strainers are required at each pump suitable valve and
piping arrangements will be included to allow transfer to and from and isolation
of all the tanks in the system there will normally be provision for separate
transfer of each grade of fuel it is usually possible to crossover systems by
removing blanking plates in the event of pump failure a typical system is shown
here you can compare it with the system on your vessel you will notice that it
shows diesel oil double bottom tanks these would not be allowed in future new
builds the tank arrangement for fuel storage should allow the different
grades and new batches of similar grades to be stored separately it should also
have the flexibility to maintain vessel stability as fuel is used during a
voyage depending on operational requirements most seagoing vessels
now use at least three grades of fuel the majority of main engines operate on
heavy fuel but we'll need to change over to distillate fuel prior to maintenance
or when the heating facility is unavailable many auxiliary engines now
use the same grade of heavy fuel as the main engine others use a lighter grade
of heavy fuel or a distillate such as diesel or gas oil also there is an
increasing need due to legislation such as Marple for operation on no sulfur
fuels in certain trading areas we will say more about these low sulfur fuels in
a later chapter you need to be aware of the grades used on board your vessel so
that you understand the storage and handling requirements for the fuel the
problems associated with storing fuel on board a ship have increased with the
wider use of residual fuels from more aggressive refining processes generally
the fuel quality has deteriorated and with this deterioration there have been
a wide range of issues to deal with microbial contamination of diesel fuel
oil has unfortunately become a common occurrence microbes are microscopic
living organisms and include bacteria fungi and yeast all of which can cause
problems in the fuel system bacteria normally the main source of problems can
be either aerobic types which need oxygen to survive or anaerobic types
which do not need oxygen when bacteria are present in water contaminated diesel
fuel colonies can form as slimy masses at the interface between the settled
water and the fuel as the colonies break up they can be carried through the fuel
system causing severe filter blockages aerobic bacteria usually initiate the
problem but as the oxygen supply reduces anaerobic bacteria can appear with the
colonies growing rapidly these anaerobic bacteria produce hydrogen sulfide which
is toxic and highly corrosive we will look at ways to deal with the problem in
a later chapter in many cases the fuel delivered to the vessel will consist of
a number of different components from the refinery process which have been
mixed together in order to meet the specification given in the fuel standard
heavy fuel oil with either viscosity or density
values outside of the limits of the fuel standard may have distillate fuel mixed
with it to try and improve its condition if the mixture is not stable then the
two components will separate out during storage
leaving the heavy fuel component in the lower part of the tank and the
distillate above it obviously the high values of density and viscosity may
cause problems when transferring or pre treating the fuel before final use you
can reduce the risk of this occurring by ensuring that the fuel storage
temperature is not excessive as this may accelerate any separation if you have
studied CBT number 179 marine fuel properties - then you will remember that
fuel oil can be contaminated from a number of sources these include the raw
crude oil the refining process and the transportation and storage stages of
supply some of the contaminants are solid material including sand soil rust
and other debris water either salt or fresh is also often present in the fuel
during storage some of the water and dirt will settle out and collect in the
bottom of the tank this has to be removed either by
draining or manual cleaning so that it doesn't carry over into the fuel systems
it also means that there has to be suitable filters and pretreatment
facilities onboard to remove any remaining water and dirt which is not
settled you will learn more about these facilities in a later chapter of this
module in compatibility is the term used to describe a situation when two
different batches of fuel each of which is normally stable react when mixed
together resulting in heavy sludge deposits in either the storage tanks or
in the pretreatment equipment the result of this condition can be that the fuel
becomes unusable and the vessels operation is seriously affected severe
sludge accumulation in the fuel treatment equipment resulting in more
frequent cleaning can mean that the treatment rate cannot keep up with
consumption requirements it should be standard practice when bunkering a new
batch of fuel that it is only loaded into empty or nearly empty tanks mixing
with previous bunkers should be avoided whenever possible in this chapter we
have seen the kind facilities required for receiving an
onboard storage of fuel oil we have looked at the tank arrangements
including the fittings required which make the arrangement suitable for
storing fuel safely we have considered possible transfer systems for moving the
fuel from tank to tank we have also looked at some of the common problems
associated with onboard storage of fuel in the next chapter we will be looking
in detail at the bunkering requirements and procedures that are in place to help
make onboard fuel handling operations safe and pollution-free before you move
on you should complete the end of chapter assessment this will give you an
indication of how much you have learned so far