AND BULK CARGOES
Purpose and general use of Seagoing bulk
Bulk carriers are single-deck vessels, designed with top-side
tanks and hopper side tanks in cargo spaces and are intended
primarily to carry single-commodity solid bulk cargo.
What is solid bulk cargo ?
Solid bulk cargo means any material, other than liquid or gas ,
consisting of a combination of particles , granules or any
larger piece of material, generally uniform in composition,
which is loaded directly into the cargo spaces of a ship
without any immediate form of containment. Example of such
dry cargo are grain, sugar and ores in bulk.
Fig : A Bulk carrier on sea passage
In its broadest sense, the term bulk carrier embraces all
ships designed primarily for the carriage of solid or liquid
cargo in bulk form, and so would include tankers. In ordinary
usage, however, the term is normally used for those vessels
designed for the transport of solid bulk cargos, typically grain
and similar agricultural products, and mineral products like
coal, ore, stone, etc., on one or more voyage legs.
General features of bulk carriers are:
1. Carrying capacity varying from 3,000 tonnes to 300,000
2. average speed of 12 ~ 15 knots
3. single deck ships, ie no tweendecks
4. small to medium sized bulk carriers (carrying capacity up
to 40,000 tonnes) generally have cargo handling gear
fitted, while larger vessels use shore based facilities for
loading and unloading
5. the cargo holds are usually large, without any obstructions, with
larger hatch sizes to allow easy loading/unloading of cargoes
6. most bulk carriers have one cargo hold dedicated as a ballast hold.
This can be used on ballast voyages for improved stability. One or
two further holds may be permitted for partially ballasting but only
7. they have hydraulic, single pull or stacking (piggy- back) type steel
8. these ships usually have four types of ballast tanks:
sloping topside wing tanks
sloping bottom side wing tanks
double bottom tanks
fore peak and after peak ballast water tank.
Coal , Iron ore, Mineral ore, Grain, Cement &
Woodchips loading in bulk
Bulk carriers are designed to load a maximum deadweight of
any type of bulk cargo from heavy ore to light grain . The
loading, carriage and finally the discharge of dry bulk cargo is
not as simple or straight forward as most people would
Many bulk cargoes have hazardous properties, or can change
their properties on passage. The ship can be easily damaged
by incorrect loading e.g. loading a forward hold to it maximum
can cause the ship to bend. This „stress‟ can have life
threatening results at sea in rough weather.
Residues from previous cargoes can also seriously effect
latter cargoes. Water damage can also have devastating
effect on some bulk cargoes e.g. cement power. It is not
easy to verify true weights or quantities of cargoes loaded
or discharged. All these factors have a serious consequence
on the methods of operation for the safe carriage of bulk
cargoes. Discharging bulk cargo using “grab”
Bulk cargoes have an inherent tendency to form a cone
when they are loaded if conveyor belts or similar systems
are not supervised and controlled. The angle formed by this
cone is known as the `angle of repose' and varies with each
cargo. Cargoes such as iron ore will form a steep angled
cone, whereas cargoes that flow freely form a shallow
angled cone. A cargo with a low angle of repose has the
potential to shift during passage.
Coal is transported on all types of bulk carriers from handy
size to VLCBs. However, it is not an easy or straight forward
cargo to handle. It can emit methane gas and it is self-
heating. In addition coal contains sulphur which causes
severe corrosion when in contact with the ship's steelwork.
In most ports the cargo is loaded wet to reduce dust. Much
of this moisture settles on passage and is pumped out
through the ship's hold bilges which means that less weight
is discharged than is loaded.
Find out more on ....coal hazards and safety precautions
This cargo is loaded very fast, 10,000 tonnes an hour is not
unusual. The loading and de-ballasting of the ship must be
meticulously planned to ensure that the vessel is not
overstressed. There is very little chance of damaging the
cargo but the ship can receive extensive damage during the
discharge operation from the equipment used.
Find out more on ....Safety precautions for loading and
carriage of iron ores
Many different types of concentrates are handled in various
parts of the world and in varying quantities. Most of these
cargoes are extremely heavy and have a low transportable
moisture limit (TML).
This means that if the moisture content of the cargo become
greater than the TML the cargo can liquefy and turn into a
slurry. When this happens on board, the cargo moves from
side to side as the ship rolls which reduces the ship's righting
lever. It does not require much cargo weight to capsize the
vessel when this happens, it a loss of stability due to free
surface effect. Some of the most dangerous cargoes where
this can happen are copper, lead or zinc concentrates,
magnetite, limonite and most pyrites.
One of the most difficult and dangerous cargoes to carry in bulk are grain cargoes.
Most grains have an angle of repose (slip angle) of about 20° from the horizontal,
which means that if the ship rolls more than 20° the cargo will shift. Then this
happens the ship will develop a large list, lying on her side and still rolling will
obviously cause a greater shift of cargo which in turn will capsize the vessel.
Most authorities therefore request that the master proves that his ship is capable of
remaining stable even if the grain cargo shifts. This is done by the compiling of the
Grain Loading Form which fully outlines the ships stability at the worse condition on
Naturally grain cargoes, like any foodstuff, are susceptible to claims with
contamination from a previous cargo and in addition can easily be damaged by
Vermin can also be a problem. Cargo holds must be clean and dry prior to the
loading of any grain cargo and most grain charters demand a survey of the ship's
hold prior to loading for this reason.
Find out more on : .Hazards and safety precautions for grain cargo
Obviously any moisture is going to ruin a cargo of cement but
probably a greater danger to the vessel is the dust that can
be produced during the loading and discharge of the cargo. If
it is not removed promptly or gets into the ship's air intakes it
can cause some long term problems to the vessel.
Salt- Salt, strangely enough, is not damaged from water, in
fact the cargo can be loaded slightly moist. However, it can
get rust stained from the ship's steelwork, therefore the ship
must cover all the steel within the cargo hold with a lime
wash solution thereby keeping the salt off the steelwork.
Again a supposedly harmless cargo that does have some
hidden dangers. Some shipments many be subject to
oxidation leading to depletion of oxygen and an increase of
carbon dioxide in the cargo hold and adjacent spaces. In
addition, woodchips can be easily ignited by external sources,
it is readily combustible and can also ignite by friction. The
stowage factor can vary greatly with this cargo depending on
the wood type, the moisture content and the type of loading
head used. Even different loading operators can achieve
varying stowage factors with the same cargo.
Structural integrity & design limitations of modern
seagoing bulk carriers
Most seafaring nations have established classification societies which
review standards for the construction of cargo vessels. Classification
societies publish construction guidelines and stability and operating
standards to ensure vessel safety and standardization of ship construction
and other marine equipment.
All ships are designed with limitations imposed upon their operability to
ensure that the structural integrity is maintained according to classification
society guideline. Therefore, exceeding these limitations may result in
over-stressing of the ship's structure which may lead to catastrophic
failure. The ship's approved loading manual provides a description of the
operational loading conditions upon which the design of the hull structure
has been based. The loading instrument or vessels approved loading
software provides a means to readily calculate the still water shear forces
and bending moments, in any load or ballast condition, and assess these
values against the design limits.
A ship's structure is designed to withstand the static and
dynamic loads likely to be experienced by the ship throughout
its service life.
Fig : Cargo hold construction of a typical bulk carrier
The loads acting on the hull structure when a ship is
floating in still (calm) water are static loads. These loads
are imposed by the:
i) Actual weight of the ship's structure, outfitting,
equipment and machinery.
ii) Cargo load (weight).
iii) Bunker and other consumable loads (weight).
iv) Ballast load (weight).
v) Hydrostatic pressure (sea water pressure acting on the
Dynamic loads are those additional loads exerted on the
ship's hull structure through the action of the waves and the
effects of the resultant ship motions (i.e. acceleration forces,
slamming and sloshing loads). Sloshing loads may be induced
on the ship's internal structure through the movement of the
fluids in tanks/holds whilst slamming of the bottom shell
structure forward may occur due to emergence of the fore
end of the ship from the sea in heavy weather.
Cargo over-loading in individual hold spaces will increase the
static stress levels in the ship's structure and reduce the
strength capability of the structure to sustain the dynamic
loads exerted in adverse sea conditions.
Special care needs to be taken with heavy cargoes such as
iron ore, scrap iron, lead and other concentrates. On general
bulk carriers with uniform hold lengths alternate hold
loading or block hold loading may be utilized to stow high
density cargoes. With such loading arrangements high shear
forces occur at the ends of the holds requiring additional
strengthening of the side shell in way of the bulkheads.
Bulk carrier business & trade patterns
Bulk carrier voyages are fixed according to market
demands. While there is a steady flow of bulk cargoes
from exporting countries to the industrial nations, floods,
droughts or other natural disasters may affect a region's
crop output, changing commodity prices. The trades may,
to some extent, be fixed with the vessel on a liner service,
but when the trade is generated on an `on demand' or
spot basis, a ship will generally not know its next `fixture'
until it receives its voyage orders.
Over 6,000 bulk carriers are engaged in the trade of bulk
cargoes, such as ores, logs, coal and steel products.
Parties in the bulk trade include:
The ship operator
the ship (as carrier) and its Master
cargo seller, ie the shipper
cargo buyer, ie the receiver or consignee
charterer (note that the ship may have been sub-
chartered to one or more charterers, but the main
contractual agreement between the charterer and the
sub-charterer is similar to that between the main
charterer and the shipowner)
insurer or underwriter
Typically, a shipowner may allow his ship to be
chartered to a charterer (who in turn may sub-charter
it). They then find a shipper who loads their cargo on
the ship. The cargo's sale has either been previously
agreed with a buyer or, in some cases, may be sold
after it has been loaded. The ship carries the cargo to
the destination and discharges to the receiver. At the
loading and discharging ports the ship, charterer, seller
and buyer may nominate agents.
To engage a ship to load a cargo, a contract of affreightment,
setting out the terms and conditions for the payment to the
shipowner in return for provision of the ship, has to be agreed
between the shipowner and the cargo owner. This agreement
can be either a bill of lading (between the carrier, ie the
shipowner or charterer, and the cargo owner) or a charterparty
(between the shipowner and charterer).
A bill of lading (B/L) is a document, agreed under the auspices
of the Hague or Hague-Visby rules, issued on behalf of the
shipowner that provides evidence that the cargo has been
received for shipment (Appendix 34). A B/L may still be issued
in addition to the charterparty agreement.
A charterparty is a written agreement (usually in a specified
format) between the shipowner and the charterer for hire of a
vessel with clearly defined freight rates, cargoes and
Cargo operation useful terms related with bulk carriers
The following definitions are extracted from the International Maritime
Solid Bulk Cargoes (IMSBC) Code 2009:
Angle of Repose
The maximum slope angle of non-cohesive (ie, free- flowing) granular
material. It is measured as the angle between a horizontal plane and the
cone slope of the material.
Dry materials that readily shift due to sliding during transport.
a. Non-cohesive bulk cargoes having an angle of repose less than or equal
to 30° These cargoes, which flow freely like grain, shall be carried
according to the provisions applicable to the stowage of grain cargoes
b. Non-cohesive bulk cargoes having an angle of repose greater than 30°
to 35° inclusive Loading is carried out using trimming equipment
approved by the competent authority
c. Non-cohesive bulk cargoes having an angle of repose greater than 35°
Loading is carried out using trimming equipment approved by the
Materials other than non-cohesive materials.
Cargoes That May Liquefy
Cargoes that contain a certain proportion of fine particles and a
certain amount of moisture. They may liquefy if shipped with a
moisture content in excess of their transportable moisture limit.
Materials obtained from a natural ore by a process of
enrichment or beneficiation by physical or chemical separation
and removal of unwanted constituents.
Flow Moisture Point
The percentage moisture content (wet mass basis) at which a
flow state develops under the prescribed method of test in a
representative sample of the material.
A state occurring when a mass of granular material is
saturated with liquid to an extent that, under the influence of
prevailing external forces such as vibration, impaction or
ship's motion, it loses its internal shear strength and behaves
as a liquid.
Materials that may react dangerously when mixed.
That portion of a representative sample consisting of water,
ice or other liquid, expressed as a percentage of the total wet
mass of that sample.
The movement of moisture contained in a cargo by settling
and consolidation of the cargo due to vibration and ship's
motion. Water is progressively displaced, which may result
in some portions or all of the cargo developing a flow
The figure that expresses the number of cubic metres one
tonne of cargo will occupy.
Transportable Moisture Limit (TML) of a Cargo
Which May Liquefy
The maximum moisture content of the cargo which is
considered safe for carriage in ships.
Any levelling of a cargo within a cargo space, either partial
Thank You for Reading
Captain Thein Win