An articulated boom can spread cargo over a wide area. By placing cargo where it is needed, self-unloaders reduce port congestion and demurrage costs because they:
Luffing and slewing
Luffing and Slewing are achieved by hydraulic action, or using tackles on some older vessels. It is most important to safeguard the boom at all times, and the Operator has to understand the entire system i.e. the manufacturers instructions its controls both hydraulic and manual, its limitations, in-built safeguards and operating procedure. He must also prevent uncontrolled movements of the boom, and take prompt action if they occur.
The Luffing Pump is not designed for continuous running, and must be stopped when luffing is completed. On Auto it is normally set to stop automatically on non-use of the switch. The oil level in the tank must be checked and valves set for operation. If the oil level is low, the float switch stops the pump from starting. It is very important to ensure visually that all securing arrangements are removed before luffing, and that the wire pendants are folded neatly so as not to get caught.
The slewing of the boom must be started, when it is clear of the parking bolster, when no other obstructions are in way, and the vessel is upright. As the boom slows it must be stopped when the listometer lights indicate, that the vessel is listing. Allow the heeling tanks to bring the vessel upright. The boom must not be slewed if the vessel lists to more than 2 degrees as the increased hydraulic loading may cause hydraulic pipe failure and the boom to swing uncontrollably.
If there is a sudden loss of power, the boom will normally remain in a locked position, and can be stowed using the emergency hydraulic power pack if required. The slewing system has thermostatically controlled heaters which must be started about two hours prior to usage in cold weather.
Uncontrolled lowering of the boom; Precaution and action
In the event of uncontrolled movement of the Boom, the Boom watchman or duty Deck Officer must immediately activate the emergency stop switch for the Boom machinery. The most likely cause of uncontrolled Boom movement is moisture or water entering one of the Boom operating switch buttons. These switch buttons must therefore be regularly checked by the Electrical Officer and renewed whenever deemed necessary. The crew must take care not to leave these control stands exposed to the elements.
Boom - head hopper and dyna- flow attachments
The boom-head attachments, and the dyna-flow trunk if used for dust suppression, must be continuously monitored by an assigned person. This is to prevent it fouling the shore installation, or to provide early warning if it shows signs of getting clogged. Clogging of the Hopper adds weight at the head of the Boom, and will cause it to bend if it is not cleared.
The portable hopper is also called the elephant foot and connects the dyna-flow trunk, to the Boom head by means of bolts. These bolts are to be intentionally cut half way through, so as to snap, if the dyna-flow trunk becomes clogged and heavy. Also, the dyna-flow trunking has lengths of chain which extend, as the transition pieces extend telescopically, and hold the extended sections. These chains are to be of predetermined weak strength (0.25 m/ton), allowing them to snap if the trunk gets caught in the shore hopper or embedded in cargo.
After lowering the Boom onto the parking bolster the lowering circuit will disengage and the parking circuit will engage. At this time, the luffing actuator has to be extended fully using the park button, which actuates a timer and allows the pump to operate for the period of time required. This ensures the freedom of movement of the luffing assembly through the link plate, which is between the luffing cylinder and the luffing beam. This prevents the cylinderhead from being damaged, during longitudinal/flexing movements of the ship in a seaway.
Always check and ensure that the luffing actuator is extended and the Link Plate is lowered on parking the boom. All the tie-downs must be used. Tie-down sensors are to be checked for proper operation. If for some reason the boom luffing actuator cannot be extended fully, the relevant Superintendent Engineer must be informed immediately.
The Boom is not designed to be rested on anything other than the parking bolster.
Our detail pages illustrated many safety aspects of Bulk carrier
Home page |||Bulk carrier types ||| Handling of bulk coal |||Cargo planning ||| Carriage of grain |||Risk of iron ores |||Self unloading bulk carriers |||Care of cargo & vessel |||Cargoes that may liquefy |||Suitability of ships |||Terminal guideline |||Hold cleaning |||Cargo cranes |||Ballast handling procedure |||Bulk carrier safety |||Fire fighting systems |||Bulk carrier General arrangement