Use of derricks on board General cargo ships

Use of derricks on board General cargo ships - safety procedure

Operation of derricks on board

Derricks for lifting cargo on board is required to be of adequate strength and stability for each load, having regard in particular to the stress induced at its mounting or fixing points , securely anchored, adequately ballasted or counterbalanced and supported by outriggers as necessary to ensure its stability when lifting.

Ships' derricks should be properly rigged and employers and masters should ensure that rigging plans are available containing the following information:-

(1) position and size of deck eye-plates;
(2) position of inboard and outboard booms;
(3) maximum headroom (i.e. permissible height of cargo hook above hatch coaming);
(4) maximum angle between runners;
(5) position, size and safe working load of blocks;
(6) length, size and safe working load of runners, topping lifts, guys and preventers;
(7) safe working load of shackles;
(8) position of derricks producing maximum forces
(9) optimum position for guy and preventers to resist maximum forces as at (h);
(10) combined load diagrams showing forces for a load of 1 tonne or the safe working load;
(11) guidance on the maintenance of the derrick rig.

The operational guidance in the remainder of this section applies generally to the conventional type of ship's derrick. For other types, such as the "Hallen" and "Stulken" derricks, manufacturers' instructions should be followed.

Velle derrick rigging

Figure 1:The rigging of Velle derrick with supporting mast

Runner guides should be fitted to all derricks so that when the runner is slack, the bight is not a hazard to persons walking along the decks. Where rollers are fitted to runner guides, they should rotate freely.

Before a derrick is raised or lowered, all persons on deck in the vicinity should be warned so that no person stands in, or is in danger from, bights of wire and other ropes. All necessary wires should be flaked out.

When a single span derrick is being raised, lowered or adjusted, the hauling part of the topping lift or bull-wire (i.e. winch end whip) should be adequately secured to the drum end.

The winch driver should raise or lower the derrick at a speed consistent with the safe handling of the guys.

Before a derrick is raised, lowered or adjusted with a topping lift purchase, the hauling part of the span should be flaked out for its entire length in a safe manner. Someone should be available to assist the person controlling the wire on the drum and keeping the wire clear of turns and in making fast to the bitts or cleats. Where the hauling part of a topping lift purchase is led to a derrick span winch, the bull-wire should be handled in the same way.

To fasten the derrick in its final position, the topping lift purchase should be secured to bitts or cleats by first putting on three complete turns followed by four crossing turns and finally securing the whole with a lashing to prevent the turns jumping off due to the wire's natural springiness.

When a derrick is lowered on a topping lift purchase, someone should be detailed for lifting and holding the pawl bar, ready to release it should the need arise; the pawl should be fully engaged before the topping lift purchase or bull-wire is released. The person employed on this duty should not attempt or be given any other task until this operation is complete; in no circumstances should the pawl bar be wedged or lashed up.

A derrick with a topping winch, and particularly one that is self- powered, should not be topped hard against the mast, table or clamp in such a way that the initial heave required to free the pawl bar prior to lowering the derrick cannot be achieved without putting an undue strain on the topping lift purchase and its attachments.

A heel block should be secured additionally by means of a chain or wire so that the block will be pulled into position under load but does not drop when the load is released.

The derrick should be lowered to the deck or crutch and properly secured whenever repairs or changes to the rig are to be carried out.

If heavy cargo is to be dragged under deck with ship's winches, the runner should be led directly from the heel block to avoid overloading the derrick boom and rigging. Where a heavy load is to be removed, a snatch block or bull wire should be used to provide a fair-lead for the runner and to keep the load clear of obstructions.

Use of derricks in union purchase

When using union purchase the following precautions should be strictly taken to avoid excessive tensions:-

(i) the angle between the married runners should not normally exceed 90° and an angle of 120° should never be exceeded;

(ii) the cargo sling should be kept as short as possible so as to clear the bulwarks without the angle between the runners exceeding 90° (or 120° in special circumstances);

(iii) derricks should be topped as high as practicable consistent with safe working;

(iv) the derricks should not be rigged further apart than is absolutely necessary.

The following examples will show how rapidly loads increase on derricks, runners and attachments as the angle between runners increases:

a) At 60° included angle, the tension in each runner would be just over half the load;

b) At 90° the tension would be nearly three-quarters of the load;

c) At 195° the tension would be nearly 12 times the load.

When using union purchase, winch operators should wind in and pay out in step, otherwise dangerous tensions may develop in the rig.

An adequate preventer guy should always be rigged on the outboard side of each derrick when used in union purchase. The preventer guy should be looped over the head of the derrick, and as close to and parallel with the outboard guy as available fittings permit. Each guy should be secured to individual and adequate deck or other fastenings.

Narrow angles between derricks and outboard guys and between outboard guys and the vertical should be avoided in union purchase as these materially increase the loading on the guys. The angle between the outboard derrick and its outboard guy and preventer should not be too large and may cause the outboard derrick to jack-knife. In general, the inboard derrick guys and preventer should be secured as nearly as possible at an angle of 90° to the derrick.

Use of stoppers

Where fitted, mechanical topping lift stoppers should be used. Where chain stoppers are used, they should ALWAYS be applied by two half-hitches in the form of a cow hitch suitably spaced with the remaining chain and rope tail backed round the wire and held taut to the wire.

A chain stopper should be shackled as near as possible in line with the span downhaul and always to an eyeplate, not passed round on a bight which would induce bending stresses similar to those in a knotted chain.

No stopper should be shackled to the same eyeplate as the lead block for the span downhaul; this is particularly hazardous when the lead block has to be turned to take the downhaul to the winch or secure it to bitts or cleats.

The span downhaul should always be eased to a stopper and the stopper should take the weight before turns are removed from the winch, bitts or cleats.

Overhaul of cargo gear

When a cargo block or shackle is replaced, care should be taken to ensure that the replacement is of the correct type, size and safe working load necessary for its intended use.

All shackles should have their pins effectively secured or seized with wire.

A special check should be made on completion of the work to ensure that all the split pins in blocks etc. have been replaced and secured.

On completion of the gear overhaul, all working places should be cleaned of oil or grease.

Use of ships cargo gear

Typical cargo-handling gear is addressed under particular ship type headings, but some general arrangements can be noted here. General cargo ships are typically fitted with derricks or deck cranes to load or discharge cargo from piers or lighters without assistance. Most tankers discharge cargo with installed pumps and generally carry sufficient cargo hose to connect to receiving terminals; many tankers have small derricks or cranes to handle the cargo hose.

Many ship types are gearless, that is, they are not fitted with cargo gear. Modern container ships rarely have the ability to handle their own containers and can load and discharge cargo only with the aid of specialized port facilities. If installed, container ship cargo gear may consist of conventional derricks or rotating cranes, or traveling overhead gantry cranes. Most bulk carriers are gearless although there are some selfunloaders with installed derrick grabs or conveyor systems for discharging cargo, particularly on the Great Lakes. Roll-on/roll-off (RO/RO) ships load cargo over ramps through stern, bow, or side ports; in the case of trailers, vehicles, and train cars, part of the cargo gear is integral to the cargo itself.

When installed and operable, a vessel’s cargo gear can be a great asset to the salvage effort. Lightering is most effective and efficient when accomplished with ship’s gear. The large number of derricks or cranes on general cargo ships facilitates loading salvage equipment and placing it in its required location on deck or in holds. Deck mounted gantry cranes are particularly useful for shifting weight longitudinally to adjust trim, weight distribution, or ground reaction; the cranes themselves are large weights that can be shifted.

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Use of derricks on board General cargo ships - safety procedure

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