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Heavy lift cargo handling - general cargo ship procedure

Heavy Indivisible Loads

Heavy indivisible loads may be defined as those which, because of their mass and/or shape cannot be handled by the normal gear available on board ship or on the quay alongside. Containers of 20-30 tonnes are handled rapidly and continuously at dedicated terminals where they are no longer considered heavy lifts. However, in ports where specialist gear is not available, they may have to be treated and handled as heavy lifts.

heavy-lift-cargo
heavy lift cargo

The techniques for handling and transporting very heavy indivisible loads have changed and become more specialised with the growth of the offshore industry, developments in onshore oil and chemical plant construction and the move to gas-fired power stations. Although the offshore market has the largest indivisible loads because they rarely move on land (other than a few metres to load out onto barges or semi- submersibles) the other markets have taken to modular construction and technical advances have created much heavier and denser loads. The newest gas turbine thermal blocks are over 550 tonnes in a small concentrated area and oil refinery reactors are frequently over 1,400 tonnes in a single tower.

National road limits vary from country to country, but the controlling factors are usually bridges that have to be crossed, elevated highway sections that cannot be shadowed by running underneath, or physical size obstructing movement where just removal of street furniture is insufficient to clear a passage. In extreme cases, buildings have been removed to allow passage and then rebuilt after movement.

Commercially, heavy lifts are divided into four groups for lift on/lift off operation. They are: There is a large fleet of vessels able to handle group (a) including many of the multi-purpose container feeder vessels and some of the remaining traditional liner vessels. A reasonable number of these are able to handle group (b) although many have restricted outreach. Group (c) is where the specialist heavy lift carriers take over as the sole operators. There are presently (2011) heavy lift vessels in service with dual gear capable of lifting 2000 tonnes and new building orders are in place for two ships fitted with 2×1,100 tonnes cranes each and thus able to lift up to 2,200 tonnes. Lifts in excess of 2,000 tonnes are usually handled by roll-on/roll-off specialist vessels, including semi-submersibles being used as deck ships.

The Load

At the time of booking and pre-planning the transport of a heavy load, the following information is vital:
Shippers will normally require diagrams showing lifting stresses together with full lashing and securing arrangements. In many cases this will be a charter party/booking note detail to be approved by both parties before booking is concluded. Shippers will often require approval of the drawings by both their own engineers and the warranty surveyor before lifting can proceed. Lashing and securing drawings will often require accompanying calculations showing the anticipated maximum forces the cargo will experience during transit on the vessel.

As wharves often have service ducting along the seaward margin, the authority at both loading and discharge ports must specify the closest permitted point of approach to the edge on the wharf, which will define the outreach needed from the ship. Some wharves will only permit landing of heavy cargo at high tide and also require prompt removal while the tide is still high, to avoid excess stress on the structure.

Preparation

A mast or Sampson post supporting a traditional heavy lift derrick should, unless suitably stiffened, be supported by not less than three stays; one leading in the fore and aft line and the others leading to each side forming an angle of about 45° with the former. Stays and shrouds should be set up taut and stretching screws securely stopped. A slack stay will not commence to function until after the mischief has been done. Careful attention should be given to the ship's plans relating to the rigging and staying of the heavy lift gear.

All leads should be set up to avoid chafing the falls. Avoid slack turns getting on to the winch barrel when winding in slack wire­the presence of such is fraught with great danger when the derrick becomes loaded. Where "steam guys" are led to a single winch, care must be taken to ensure that the weight of both remains balanced, and that one does not become slack during any stage of the operation. It is sometimes the practice to overcome this problem by securing the end of the topping lift purchase to a yoke which in turn supports the end of each steam guy. Thus although the derrick may be topped or lowered a weight is maintained on the steam guys no matter at what angle the derrick is operated. In these circumstances care must be taken to ensure that the yoke is so positioned that it will operate correctly.

It is important that the vessel is trimmed to an upright position before heavy lift operations commence. In many instances vessels are fitted with fast-flooding ballast transfer tanks. Additionally, the vessel should not only be upright when lifting commences, but should, if possible, be maintained close to that position throughout the operation by use of ballast tanks. When a vessel is working heavy cargo with its inherent risks, all crew should be on deck and all non-essential shore personnel should be put ashore for their own safety.

The Gear

In the U.K. a heavy derrick, crane or hoisting machine with its gear, has to be tested with a proof load which should exceed the safe working load as follows:

Safe Load Proof Load
Up to 20 tonnes 25% in excess
20­50 tonnes 5 tonnes in excess
Over 50 tonnes 10% in excess

The gear should be adequate for the load, including any extra weight, e.g. for lifting tackle, which itself may well weigh many tons.

The heavy lift derrick should not be operated in a depressed condition, i.e. near the horizontal, since if the vertical component of the thrust becomes low, there is danger of the heel springing out of the shoe.

When using container cranes to handle uncontainerised heavy indivisible loads, there may be provision for a "rams horn hook" to be installed in place of the container spreader. In some instances the spreader has special lugs to which lifting wires may be shackled and the heavy lift supported directly by the spreader. Where shore gantry cranes are used, it must be ascertained that the port of loading and port of discharge have cranes of suitable capacity, with the necessary distance between the legs (and/or a revolving spreader) to allow the load to be handled.

The gear in use should be exactly as indicated in the diagrams that have been approved by the shipper's engineers or warranty surveyors and match the calculations that have been approved.

At all times check the validity of all parts of the lifting gear, including all loose items, before contracting to lift.

Tackle

Slings should be made up of the appropriate wire or chain to provide an adequate safe working load, and of the correct length so that they do not damage the cargo and do not require shortening because of too long a drift.

The two ends of slings should be connected to the block of the derrick with the eyes on the bow of the shackle and not on the pin, especially if the drift between lift and shackle is short and the spread large­which should be avoided where possible.

Slinging should be set up in such a way that the load remains level. However there may be occasions when, to allow a particular awkwardly shaped load to enter the hatch square, the load will have to be slung at an angle. If this is the case it must be ascertained that the load itself will not be damaged by such treatment, and the slings made up accordingly.

Where goods may be become crushed, or where the length of the load is such that the angle of the sling will create unacceptable bending moments on the load, the use of a spreader, or beam may be required. As mentioned earlier the weight of any such tackle must be included in the calculations for the lifting gear.

Full use must be made of all proper lifting points on the load, and those points which are marked as suitable for placing the sling.

Use only the certificated tackle as approved in the lifting and securing diagrams.

If, for any reason, an exact following of the lift and securing diagram is not possible and additional or different tackle is required, err on the side of caution and use higher rated tackle. If new calculations can be approved for lesser tackle then this can naturally be done, but always check all calculations done by others before proceeding.

Vertical and Horizontal Movement

Careful winch driving is essential to avoid the gear being put to undue strain. Too great a speed of operation increases the strain on the hauling part and may be dangerous if for any reason it should become necessary to stop suddenly.

When lifting or lowering into or out of the hold, weight should be slowly taken up or lowered down so as not to stress the gear.

When traversing either in or out of the hold from or to the shore the vessel should be maintained as close as possible to upright using ballast.

When lifting from or lowering to the wharf, the weight must not be taken up or taken off by use of power alone. If possible, when lowering a heavy load to the ground after just touching, when almost all of the weight is still on the hook, the vessel should be ballasted further down to take the weight from the hook. If this is not possible then a falling tide can do the same as ballasting down, but may be slightly slower. Unwinding the weight too quickly direct from the winch will cause the vessel to heel and possibly drag the heavy lift with it, creating dire consequences. When lifting, a rising tide can be used if de-ballasting is not an option. In a closed dock situation, where moving ballast is not an option, then all movement should be very slow and carefully monitored.

When transferring a heavy lift contracted for water/water movement, the calmest conditions possible are needed and the added difficulties involved should be taken into account when contracting. Landing or picking up a floating heavy lift in even a small swell puts excess stress on all parts if the equipment.

Stowage Requirements

The stowage position selected for a heavy lift must be that which can best support its weight. Additionally, there may be a requirement to have the lift in such a position in the ship that the g-forces generated by pitching and scending will not affect the load or its securing.

The load should be positioned so that heavy point loading is not exerted on deck or tank top plating in between frames and beams. When this is not possible, bearers should be provided to spread the load. Usually bearers are laid fore and aft or diagonally to achieve the maximum support from floors and beams. Load spreading should take into account both the transverse frames and the longitudinal strengthening.

Heavy lifts should be stowed in a position that can be directly plumbed by the lifting hook so that dragging is not required for either loading or discharge, i.e. in the hatch square of a general cargo ship. Other factors to be considered to expedite the safe loading, carriage and discharge of a heavy lift are:
  1. The lift should be prominently marked with its weight, centre of gravity and lifting points by the manufacturer prior to arriving alongside the ship. Items marked with conflicting information, particularly regarding weight, should not be shipped until such information has been verified;
  2. Individual heavy items should not be consolidated into a single unit using inadequate securing as this will affect the requirements of 1 above and also risk an accident if securing fails;
  3. Individual lifts should not be tightly stowed leaving insufficient space for slinging at the discharge port;
  4. The use of plenty of bearers and dunnage;
  5. Lifts must be handled and stowed in accordance with markings on each piece and/or instructions from the shipper, e.g. "This way up" means exactly what it says.
In container ships (or general cargo ships so-fitted) pads provided for container stowage may be used directly for the support of uncontainerised heavy lifts. Another method of supporting the lift is to use flat rack platforms located in container stowage positions with the heavy lift placed on them. However, it should be borne in mind that a heavy lift carried on the tank top of a cellular vessel will likely mean that the container slots vertically above the lift are not available for loading.

Restraint

As mentioned earlier the cargo may have to be restrained during the loading operations particularly if it is on a low friction device such as air or water skids. Once stowed in position lashing, securing and tomming must be carried out to prevent the slightest movement of the load. All lashings must be set up tight and wooden tomming must be secured in such a way that it cannot be dislodged by ship vibration, working or movement. As a rule of thumb, a total lashing on one side of a load should have a combined breaking strain of at least l½ times the total weight of the load to be restrained. Tomming and chocking would be extra to this.

All lashing and tomming should utilise the appropriate and approved points on a load to give the support. Where necessary extra securing points will have to be welded or riveted to ships' frames and decks.

Lashing and securing should follow the approved securing diagrams and gear used should be of the specification detailed.

The higher the centre of gravity the more the heavy lift will tend to lift in a seaway, so sufficient downward lashings are required.

Where possible, weld bracing to the deck to hold the load in position and any additional methods of securing that can be welded direct to the deck/tank ceiling should be used. Always remember safety rules when welding over tanks! Wooden tomming is insufficient on really heavy loads and steel restraints should be used.

After completion of discharge remove all welded securing devices, grind smooth and coat to avoid damage. Remember the underside of tank ceiling /deck plate will also have been damaged and need recoating.

Loading

The ship should be upright when loading (or discharging) a heavy lift and have adequate stability.

The double bottom tanks must be either pressed up or dry. If ship's gear is being used it must be remembered that the effective centre of gravity of the load moves to the derrick head as soon as the lift is floated.

Lifting operations should be interrupted to carry out checks on the slinging arrangements:
  • a. as soon as the weight is taken by the slings.
  • b. when the load has been lifted a short distance. The whole system should be checked through to ensure that no undue strain is being imposed on gear, equipment, or the load itself.

  • Clear lines of communication should be established between all those involved in the operation, with one person only in charge. It may be necessary to discontinue other operations close by on ship or shore to allow those involved with the heavy lift to hear and understand the control signals.

    Discharging

    Similar precautions should be taken to those described under "Loading". Furthermore, it may be that the vessel, being at the end of a voyage or passage, has less bottom weight in the form of fuel and/or water. This will have to be taken into account when considering the stability requirements. It should also be borne in mind that when a heavy lift is hoisted from its place of rest the centre of gravity of the weight is transferred to the derrick head. Again it is important that one person only should be in charge of the operation and that all activities are pre-planned with appropriate stops to check equipment and gear.

    Occasionally heavy lift cargo has to be offloaded straight to the sea. This might be a requirement of semi- submersible vessels or a requirement of the cargo itself e.g. lighters, launches, cylindrical and rectangular tanks, etc. In such cases, provided that the pieces are of sufficiently strong and robust construction to withstand the stresses and falls, they are carried on deck and launched over the side at destination.

    Cylindrical objects, which must be perfectly watertight and free from small protruding parts, should be mounted on a strong launching structure built of timber, the inboard end of which rests on top of the adjacent hatch and the other on the bulwark, adequately supported at intermediate points. The frame of the structure should incline about 2° in the direction of the ship's side.

    The discharging is a simple process and is affected by listing the vessel in the desired direction by means of water ballast or fuel oil. Tanks not in use for that purpose should either be empty or pressed up and it should be borne in mind that when the weight drops off, the vessel will roll sharply in the opposite direction.

    For lighters, rectangular tanks, etc., a similar structure is built, extending a little beyond the bulwarks.

    On top of the main structure a movable cradle-like arrangement is built to the shape of the craft so as to support it at three or four different points, according to its length. This is mounted on launch or slipways formed integral with the main structure with suitable means of locking it into position. The craft is secured by wire lashings to prevent movement during transit and is launched overboard sideways by giving the ship the necessary list.

    After Discharge

    It sometimes becomes necessary to unship stanchions when stowing heavy lift cargo. All such, forming as they do important parts of the structural strength of the vessel, should be properly restored and secured in their original position before stowing any cargo on the decks above.

    When it is not possible or convenient to restore all stanchions into position without seriously embarrassing the stowage, heavy shores of timber laid on stout timber fore and aft bearers should be fitted and tightly wedged into position to carry the weight of the deck above. Neglect to do so will likely result in the deck being set down.






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