Various bulk cargoes free flow ability - Self-unloaders procedure

Self unloading vessels are dependent on the free-flow ability of the cargoes, as well as gravity to bring down the cargo steadily through the gate. The flow ability of a cargo can be estimated by its angle of repose. The angle of repose of a material is the angle made by the surface of a freely formed cargo pile to the horizontal. This gives an indication of readiness of the cargo particles to flow. Generally, the lesser the angle of repose, the higher will be the flow ability.

For example, grain has a low angle of repose whereas that of a gypsum is high. Free flowing cargoes have angles of repose less than 20 degrees, quite free flowing are between 21 to 30 degrees, moderate are between 31 to 40 degrees, and sluggish are those above 40 degrees. However, this is a general estimate. The material flow-ability is also determined by factors such as dry or damp, lumps or fines or a combination, rough or smooth surfaces, duration of voyage, loading conditions, exposure to weather of pile onshore, winter or Summer. Cargo sweating can also be a factor, and in winter, actual ice formation may compact the cargo. So, the same cargo will flow differently at different times and conditions.

Fig: Gravity-type self unloader system on the 28,400dwt STONES

Fig:Self unloader American Republic awaiting cargo

While loading the cargo and taking into account the expected conditions on passage, a judgement must be made on its expected flow-ability. The relevant Management Office and Owners are to be notified of expected delays at the disport; affecting the discharge rate.

Precautions Against Hang-Ups:

Ensure UHMW lining is in place.
Vibrators are operational.
Close the hold immediately on completion of loading.
During discharge, it is important to avoid breaks in the flow of cargo through the gate. When the cargo at a gate shows signs of finishing, then the adjacent gate should start to be opened, avoiding any overloading of the belt, by maintaining a relatively small flow.

Entry into Cargo Holds

This is an essential operation when cleaning the remains of certain types of cargo, or when unloading a troublesome cargo which forms large hang-ups. The cargo holds are a dangerous place to work, when the vessel is unloading due to the fact that the bottom of the holds are not flat, and are lined with UHMW plastic sheeting.

Man entry into cargo holds in order toea cr l hang-ups is prohiibted until a full risk assessment has been carried out and the risk lveels deemed to be acceptable (i.e. 1 or 2) once additional precautions have eben taken. The complete riska ssessment with photographs is to be e-mailed to the vessel control group for office apapnrdo val authorisation.

Precautions to consider are to include as a minimum the following:

The Master, Chief Engineer and Chief Officer must be informed before entry is carried out.
The gate Operators must be made aware of the location of the entry team.
An entry team must consist of at least two people.
An observer with a radio, and the conveyor emergency stop button must be positioned at the hatch coaming keeping constant close watch on the entry team.
The entry team will use the fall arrestor attached to their safety harnesses when climbing up or down the hold access ladders.
The entry team must work from the aluminium work platforms provided when working on large hang-ups, as these offer a means of escape if the pile suddenly collapses.
Gates must never be left unattended.

Related information

Our detail pages illustrated many safety aspects of Bulk carrier

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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 Contact us

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