Ship Unloading
Solutions
Hans van Est, Van Aalst Bulk Handling BV, the Netherlands,
outlines the benefits of pontoon-mounted ship unloaders for
use in a wide range of applications.
Introduction
Most ship unloaders for cement and other dusty abrasive products are installed on the dock in harbours. For
small ships the unloaders can be fixed to the dock, making it simpler to move the ship up and down to enable
the machinery to unload all of the ship’s hold.
However, larger ships (bigger than 5000 dwt) are more complicated to move along the dock; on many
occasions a pilot is needed to carry out transportation of the ships. Unloaders for larger ships are
designed to be mobile. The ship stays moored at one location in the harbour and the unloader is moved
from hold to hold. The ship unloaders can be installed on rubber tyres or on boogie sets on rails.
Figure 1. A ship unloader for
cement in Trieste, Italy, with
a capacity of 275 tph and
able to unload ships of up to
15 000 dwt.
In some situations, a better solution would involve
installing a ship unloader not on the dock, but on a
pontoon. Van Aalst Bulk Handling BV has delivered a
number of pontoon-mounted ship unloaders over the
years and is currently installing one on a pontoon in
Bangladesh. This article will address a number of different
installations of pontoon-mounted ship unloaders carried
out by Van Aalst in connection with their specific local
circumstances, including:
ll Low draught at the dockside.
ll A narrow and/or weak jetty.
ll Large differences in water height.
ll Wide mobility range for big and heavy ship unloaders.
Low draught at the dockside
At several harbours, the water level close to the dock is
shallower than the depth further from the dockside. The
further away from the dockside, the deeper the draught
Figure 2. A ship unloader for cement in Rhode Island,
USA, with a capacity of 600 tph and able to unload ships
of up to 45 000 dwt.
of the ships can be. Even after dredging, the situation will
improve for only a short period.
Installing the ship unloader on a pontoon results in
the possibility of placing the equipment several metres
from the dockside (Figure 1). Ships of 15 000 dwt can
be unloaded from this position, compared to ships of
3500 dwt that could previously be unloaded at dockside.
Figure 1 illustrates the ship unloader in operation in
the beautiful harbour of Trieste in the northeast region of
Italy – the same solution as was required in Bangladesh.
The terminal in Italy is very close to the marina and a
pneumatic unloader provided the most environmentally
friendly solution with regard to dust emissions.
The pipeline to the storage hold was installed along
the gangway to the pontoon with two flexible connections
– one at the shore side and one at the connection
between the gangway and pontoon.
An extra advantage of a ship unloader on a pontoon
is that tidal differences have no influence on the
height difference between the unloader and the ship.
Consequently, the suction arm of the ship unloader does
not have to be designed with extra length to compensate
for tidal difference. The ship and pontoon always stay at
the same water level. A longer suction arm requires larger
vacuum pumps and, for this reason, a ship unloader on the
dock will consume more power than a pontoon-mounted
unloader.
The ship unloader in Figure 1 is fixed at one position;
here the ship has to be moved during unloading to allow
all holds to be emptied. In the description below of an
installation where there is a narrow or weak jetty to
accommodate, this disadvantage is solved.
Narrow and/or weak jetty
Figure 3. A ship unloader for cement in Newark, USA,
with a capacity of 600 tph and able to unload ships of up
to 45 000 dwt.
In harbours with narrow docks, or docks with limited
strength, a pontoon-mounted unloader can provide the
right solution.
At this unloading terminal, the pontoon can be moved
along the ship from hold to hold – this is a big advantage.
In this case, ships up to 45 000 dwt have to be unloaded
and it would prove very difficult to move this size of ship
up and down in front of a ship unloader that remains in a
fixed position. Small separation pontoons at the front and
back of the ship secure a space between a ship and the
dockside, making it easy to move the pontoon-mounted
ship unloader.
The ship unloader shown in Figure 2 is integrated
into the pontoon. When operating in the US, the pontoon
is constructed according to ABS (American Bureau of
Shipping) standards. Facilities such as a canteen for the
operators and a storage room for spare parts are provided
on board. Note that not all unloaders of this type are
integrated in the pontoon.
Temporary solution
On some occasions a harbour extension will not
be completed upon the arrival of imported cement
shipments. The ship unloader must operate in a different
part of the harbour until the construction work is
Reprinted from May 2014
World Cement
\
Figure 4. Two ship unloaders with identical capacity.
concluded. At the final position of
the cement import terminal, the
ship unloader will be dock mounted
and movable on rubber wheels.
During the in between period, the
wheel sets of the ship unloader can
be temporarily removed and the
unloader installed on the pontoon
(Figure 3). As soon as the extension
in the harbour is finalised, the wheel
sets can be reinstalled and the
ship unloader can be lifted onto the
(new) dock.
This type of ship unloader was
also delivered for use in Newark,
USA. However, in this case the ship
unloader was not integrated in the
pontoon, but temporarily lifted onto
a pontoon. This pontoon does not
have to be constructed under the
strict ABS rules – it can be any
available pontoon.
If there is sufficient available
dock space and strength,
a dock-mounted ship unloader is preferable, as
transporting the ship unloader on wheels is much
simpler than moving the pontoon.
For this project, the size of the ship unloader is
notable. Van Aalst Bulk Handling is capable of building
much more compact mobile ship unloaders, compared
to unloaders produced several years ago (Figure 4).
Both ship unloaders have a capacity of 600 tph and can
unload ships up to 45 000 dwt. The unloaders shown
in the photographs are all diesel driven and require no
power supply from the shore.
Figure 5. A ship unloader for alumina in Neus, Germany,
with a capacity of 275 tph and able to unload ships of up
to 3500 dwt.
Large differences in water height
Water height differences can be caused by tides – in
the UK these can be more than 4 m. Terminals along
rivers can also suffer from huge water level differences.
For example, at a terminal in Neus, Germany, the
water level of the Rhine River varies by up to 6 m in
the summer and winter months (Figure 5). This ship
unloader unloads river barges carrying alumina and
pumps the unloaded alumina to storage silos on
shore.
The water level at this terminal does not change twice
daily with the tide, but over extended periods depending
on the season. This presents the possibility of shortening
or lengthening the vertical steel transport pipeline in
sections (Figure 5) during periods where no ships have
to be unloaded. Small movements of the pontoon (when
a ship passes by) are compensated by a short flexible
connection hose between the pontoon and the fixed
convey line.
As well as the draught problem in Bangladesh, the
water level at various terminals along the rivers poses
the same problem experienced at the Neus terminal in
Germany. Thereby, this solution was also chosen for
use at various terminals in Bangladesh, where large
quantities of flyash are imported from India. By installing
the ship unloader on a pontoon, the flyash can be
unloaded during all seasons.
Wide mobility range
By mounting the ship unloader on a pontoon, it can be
temporarily moved to any location or harbour where
large amounts of cement are needed. These demands
can arise as a result of major infrastructure projects,
such as the Olympic Games or a hydropower
dam. Following completion of the project, the ship
unloader can be transported to a new location. No
harbour modifications are needed for supplying large
construction projects and there are no obstructions to
existing operations during this period. It is even possible
to store the unloaded cement in the pontoon and create
a floating silo.
Reprinted from May 2014
World Cement
/