Gate operation objectives
- To identify the gate for the hold that it serves.
- To maintain a steady discharge, at the rate required.
- To prevent overloads and spillages.
- To ensure the careful operation of the gates.
The following factors are to be taken into account:
- Type/design of the gate.
- Flow ability of the cargo.
- The rate set by Cargo Control Room indicated by the traffic lights.
- Correct operating pressure in the lines.
- Stage of discharge, i.e. level of cargo in the hold.
- Any dangerous build up of cargo in the hold.
- Its distance from the transfer area, the further away the more the belt is loaded, and the
chances of overload are therefore greater.
The ‘sluice’ type gates drop the cargo onto the belt, whilst the ‘bucket jaw’ type tends to lay the cargo
onto the belt in the direction of its travel. Care must be taken not to dump the cargo onto the belt, as
this will cause a spillage. The gate should be opened by jerking it partly at first, and the
incremental stages, watching the traffic lights at all times. As the belt travels with the load, the light
may suddenly turn to red in which case start closing the gate. If the red light remains on, close the
gate and re-open it when the light returns to amber, then set that flow.
There will be a time lag
between the lights, and the increase or decrease of cargo allowed on the belt. The traffic lights must
be watched all the time and kept safely on the ‘amber’ light, between ‘red’ and ‘amber’ nearer the
transfer area, and to between ‘amber’ and ‘green’ away from the transfer area. If the red light tends to
remain, reduce the flow immediately. The time taken for the load sensors to sense the change in load
must be borne in mind.
To maintain a steady rate of discharge, before changing gates, it may be prudent to jerk a trickle from
the next gate to ensure that it will flow when required.
Means of communication must be tested taking the noise levels in the tunnel into consideration. The
tunnel light and sound signals code must also be understood by all Gate Operators.
Directing gate operators
When directing the Gate Operator: at the ‘start-up’ during the dipping stage, and when lightening a
vessel for low water, it is imperative that the Chief Officer controls the gates to be used, to effect an
even-keel bodily rise of the vessel.
During the main discharge, the Gate Operators are to follow the sequence on the discharging plan, and
their movements are to be reported to the Cargo Control Room and the Duty Officer. The Duty Officer
is to monitor the movements of the Gate Operators and ensure compliance to the discharging plan.
It is the cargo itself, that helps the cargo to slide. With gypsum, the lumps and stones slide over the
fines and bring down the fines with them. Cargoes such as aggregate of stone, iron ore or pellets, and
coal have a good flow ability.
When the cargo flow is erratic, the Gate Operators must be cautious for
sudden cargo slides which will shoot past the gate, and cause an overload/spillage. The Duty Officer
must warn the tunnel of any such tendency or build-up in the hold, which could fall onto the open gate.
When using the Vibrators never open the gate fully, as the cargo may fall suddenly. When moving to
the next gate it is essential that the previous one is closed and isolated.
During draining, the Duty Officer is to guide the Operators by hold and gate number. The draining of
hold gates is to be carried out methodically, and assisted by the use of Vibrators if necessary. The
method of draining a hold has to be perfected by practice, and the knowledge of the flow-ability of the
The vessel is to detail the ship specific actions taken if the following problems occur:-
- Gate blockage
- Gate off track
- Loss of gate power
- Foreign object in way of a Gate
- Actuation of the Emergency Stops
These actions are to be documented and explained at meetings.
The Master, Chief Engineer and Chief Officer must liase closely before and during the unloading
As the operation is highly mechanised Cthheie f Engineer is more involved in cargo
operations than on a conventional vessel. As a result the actual operation of the unloading
system falls directly under his control.
The Deck Department are to provide an unloading plan which will state the sequence of ballasting
The Tunnelmen and Electrician(s) are primarily responsible for the operation of the unloading
equipment, however during long unloading periods it is necessary to draft in Crew from other
departments. It is therefore necessary to train personnel from the Deck and Engine departments,
mainly the Ordinary Seaman and including Cadets, to operate the tunnel gates and maintain a watch
during unloading. This will allow the unloading equipment to be operational for extended periods whilst
complying with the STCW regulations regarding crew working hours.
In the case of long discharges it
will be necessary to split the tunnelmen into two teams, in order that they can monitor the operation of
the unloading equipment, whilst other personnel operate the gates. One Tunnelman is to walk-round
the entire system once an hour, while the other Tunnelman remains in the tunnel operating the gates,
and overseeing crew from other departments.
The duty Deck Officer is to maintain an effective cargo watch, which is to include orders for ballasting
operations, and the maintenance of the vessel in an up-right condition. The Boom must be kept clear
of the cargo pile at all times, and one man must be stationed at the boom controls during the entire
discharge period, to attend to adjustments.
Overloads and spillage's
Common causes for spillages:
If the cargo is comprised mainly of fines, these may pass through the scrapers and cause a gradual
build-up of cargo in the vicinity of pulleys. To minimise this, the belt cleaners or scrapers that are not
functioning correctly, must be adjusted or replaced.
Spillage and resultant overload can be caused when the cargo suddenly slides through an open gate
and therefore Gate Operators must remain alert. Warnings of sudden cargo slides must be given by
the Duty Officer. Cargo may bounce off the running belt, especially in the case of a mass-flow gates,
and if not checked, may damage the undercarriage.
The gates must be operated with great care and
should any cargo fall onto the underside, the belt must be stopped. Blunt long-handled rakes are
provided to remove such fallen cargo, and the utmost care must be taken while using these.
Material spillage from the Loop belt may be as a result of the following:
Trash pumps operation
- Incorrect belt alignment.
- Low belt tension.
- Nominated Charter Party cargo lump size exceeded.
The Trash Pumps are provided at the tunnel bilge wells, and are also capable of pumping out slurry.
Care must be exercised whilst using them, to avoid damage to their impellers by trying to force cargo,
such as stone or iron ore pellets through them.
If for some reason water has accumulated inside the tunnel during discharging, it must be established
that this water does not contain cargo residue, or any trace of oil.
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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"A bulk carrier which is intended primarily to carry dry cargo
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- Self unloader components
Function of loop & bucket belt elevators
Self unloaders various cargo handling gears
- Various type boom conveyor belts - How the belt sytem practically works ?
Dealing with self unloaders stalled lift belt
Conveyor belt construction & troubleshoot guide
Conveyor belt installation guide
Conveyor belt repair & maintenence guide
Safe working practice onboard self unloading bulk carriers
- Preventing conveyor belt fire onboard self unloading bulk carriers
- Cargo work safety precautions
- Various bulk cargoes - free flow ability
- Various bulk cargoes & dealing with cargo hang ups
- Navigation in
Ice & safety precautions
- Dust suppression procedure & environment protection
- Preparations for cargo planning, handling & stowage
- Maintaining safe stability onboard self-unloading bulk carriers
- Procedure for bulk cargo handling prior to and during loading
- Loading operations - voyage orders, draft restrictions, various grades and rates
- Loading sequence and other related considerations
- Preparations for discharging & related guideline
- Self unloaders discharging operation
- Safety precautions for boom operation
- Cargo holds/ tunnels cleaning, maintenance and check items
- Procedure for transporting coal on self- unloading bulk carriers