Cargo holds and hatch cover strength requirement for a seagoing bulk carrier
To carry the maximum amount of cargo, bulk carriers
are designed with a high block coefficient (Cb), ie their
hulls are given a full form.
Cargo holds have large unobstructed hatches to
facilitate the process of cargo loading and discharging.
The ship's holds also have hold bilges for drainage in
the form of two wells, one on each side aft the hold.
The bilges are used to collect water from the tank top
and must not be more than half the height of the DB
tank. They may also have high level bilge alarms to
track the level of water in them.
On ships that discharge bulk cargoes using grabs,
bulldozers or hydraulic hammers, the tanktop
(the deck of the cargo hold) has to be additionally
strengthened during construction.
Bulk carriers built after 1998 are fitted with water level
detectors and audible and visual alarms as follows:
- In the aft of the cargo hold
one alarm to warn when the water level is
above the inner bottom reaches 0.5 m
a second alarm to warn when the water level
reaches a height of either 15% of the cargo
hold or 2 m
- an alarm in the ballast tank(s) forward of the
collision bulkhead to warn when the water level in
the tank reaches 10% of the tank capacity. This
alarm, along with the one fitted in the ballast hold,
can be deactivated when the compartment is
used for carriage of a liquid
- an alarm in any dry or empty space (except the
chain locker) that extends forward of the first
cargo hold to warn when the water level reaches
height of 0.1 m above the deck of the respective
Fig:Steel hatch cover arrangement on a bulk carrier
Hatch openings are covered by weathertight steel
hatch covers extending to between 45 - 60% of the
ship's breadth and 57 - 67% of the length of each
From the bow (forward perpendicular) back one quarter
of the ship's length, hatch covers need to withstand a
load of 1.75 tonnes per metre. Aft of this, hatch covers
must withstand a load of 1.30 tonnes per metre. The
forward hatches have coamings at least 600 millimetres
high and at least 450 millimetres high aft of this.
Modern bulk carriers use hydraulic hatch covers that,
generally, open in a fore and aft direction (for folding
hatch covers) or athwartships (sliding hatch covers),
Mechanical Hatch Covers
The most common are steel hatch covers, which may
be of folding, sliding or rolling types, fitted with securing devices to make them
weathertight . They are commonly
opened or closed by either a hydraulic or an electric
rolling system using a single control.
Steel Pontoon Covers
Using gantries to lift and stow hatch covers, portable
steel hatch covers are used and made weathertight by
securing devices such as cleats, cross joint wedges,
etc. A `piggy-back' type hatch cover is sometimes used
Piggy backing pontoons means that during loading
some hatches will be closed with another hatch
pontoon on top. When switching to load the next
hatch the loading hatch must first be closed, and
then the next hatch to be loaded opened with its
pontoon placed on the previous hatch. To minimise
the time lost to moving between hatches, extra care
must be taken in the initial planning of the loading
Fig: Watertight hatch covers arrangement
To keep hatch covers weathertight, effective sealing
is required between the coaming and the hatch
cover. To achieve the seal the compression bar exerts
pressure on the rubber gasket. Once properly sealed,
the hatch covers are secured in position against the
coaming during sea passages by a `quick acting cleat'
mechanism between the hatch covers and the coaming.
Cross joint wedges are used to seal panels or pontoons.
These exert pressure on the adjacent pontoon top
which in turn exerts pressure on the compressor bar
between the pontoons to achieve weathertightness.
Fig: Maintenance of hatch cover vents is essential
After each load/discharge and before hatch closure,
all coamings must be cleared of any cargo residue to
avoid damage to the hatch seals. Damage at this point
could easily compromise the weathertight integrity of
the hatch lid, resulting in damage to cargo. Drainage
pipes and non return values at the coaming corners
will need to be cleared.Hatch Jacks
After each use these jacks must be inspected for
possible leaks especially at the seals, which will soon
show signs of leakage. The pipe connections that run
under the coaming of these various joints, are also prone
to leakage (in the same manner as the jacks). This, in
turn, can lead to slippery decks and possible accidents,
including overboard discharge causing pollution.
Chains and Rollers
On older ships, the chains will have stretched through
long usage and this will, in turn, cause problems when
closing hatches as the jack-up points may not centre over
the jacks. Rollers will also show wear on the bearings
and split pins, and replacements may be required.
As with all other parts of the hatch, cross joint cleats/
wedges will need to be checked as they will suffer from
wear that can compromise the watertight integrity of
the lid. In the case of quick acting cleats, the rubber
bush will need to be replaced at regular intervals.
Owing to the natural working of the ship at sea, weather
permitting a daily check of the hatch cleats (including
hydraulic) should be made to ensure that they are tight.
These cleats should not to be bar tight as this could
cause severe compression damage of the rubber seats.
Corrosion prevention methods for bulk carrier
Maintenance procedure for mechanical steel hatch covers
Structural standards & strengthening of bulk carriers
Indication of unusual motion or attitude of bulk carriers and risk management / evacuation
Deterioration of ships structure and consequences of forward flooding
Handling water ingress problems in bulk carrier, investigation and countermeasures
Operation of sea going bulk carriers involved numerous hazards . Careful planning and exercising due caution for all critical shipboard matters are important . This site is a quick reference to international shipping community with guidance and information on the loading and discharging of modern bulk carriers so as to remain within the limitations as specified by the classification society.
It is vital to reduce the likelihood of over-stressing the ship's structure and also complying with all essential safety measures for a safe passage at sea. Our detail pages contain various bulk carrier related topics that might be useful for people working on board and those who working ashore in the terminal. For any remarks please
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- Indication of unusual motion or attitude of bulk carriers and risk management / evacuation
- Deterioration of ships structure and consequences of forward flooding
- Handling water ingress problems in bulk carrier, investigation and countermeasures
- Hull stress monitoring system for bulk carriers
- Suitability of Shore Terminals for handling bulk cargo
- Preparation for ships carrying bulk cargo & standard loading condition
- Bulk carrier types - Ore carriers, OBO ships, forest product carrier , self unloader and more