The consequences of not correctly securing non-standardized cargo
– damage to/loss of cargo
– fines – recovery costs
– repair costs
▬ Loss of reputation
▬ Safety of ship and crew
▬ Lost cargo is potentially a “wreck” under the Nairobi International Convention on the Removal of Wrecks (which came into force on 14th April 2015)
– “Wrecks”, if not removed, may pose a hazard to navigation
– Does the “wreck” pose a hazard to the environment?
– Who is responsible? The onus to remove the “wreck” is on the registered owner
– What measures can and are to be taken based on such a responsibility? – How can the responsibility be enforced?
▬ Cargo becomes a hazard (seaworthiness issue)
▬ Liability for re-stowage costs
▬ Liability for the value of the goods lost
▬ Liability to the owners of other cargo damaged by the unsecured movement of the goods in question ▬ Liability to the ship’s hull for damage to the same
▬ Liability for potential damage caused by the goods lost overboard as flotsam
▬ Costs related to the location and removal of goods lost overboard
The causes of not correctly securing non-standardized cargo
The securing of non-standardized cargo requires careful planning by experienced personnel. Shipping this type of cargo is frequently non-routine and the shipper (who may also be the charterer), as well as the ship’s crew, may have relatively little experience in securing different loads. Specialist carriers generally have dedicated departments of mariners and naval architects, but many general carriers do not and may lack competence in this area. Experience has shown that often the cargo has been packaged for transport by road but is not designed for securing and transporting on a ship. In addition to protective packaging, any supporting grillages/cradles may not be suitable for seagoing transportation and are not strong enough to support the changes in weight distribution of the cargo as the vessel pitches and rolls. Initially, a plan of the cargo should be requested showing strong/securing points. These will need to match up to the securing arrangements on the ship. It may be necessary to employ a suitably qualified company to produce a lashing plan. An appropriate ship which has suitable securing arrangements should be selected for the carriage of the non-standardized cargo. However, ships fit for non-standardized cargoes are becoming fewer with the increased use of containerisation. This makes the planning even more critical. If a Port Captain is assigned to oversee the stowage, it is important to ensure he or she has experience in this type of work and is competent. This is particularly important if he or she is contracted in. Once the planning is completed and a suitable ship has been selected, the lifting gear must be checked to ensure it is suitable for the cargo and is in good condition. This may require supplying dedicated lifting gear (possibly with spreaders) designed for the non-standardized cargo. The cargo should be placed on good quality dunnage to increase friction. The cargo should not normally rest directly on a steel deck. The dunnage should reduce damage and prevent heavy or sharp pieces of cargo (if any) from coming into contact with the ship’s side plating. If welded sea fastenings are used, the welding must be of a good standard and preferably NDT checked. Finally, the lashing gear used must be suitable for the cargo and in good condition with proper certification. Items such as shackles/ratchet straps/bulldog clips must be used as designed and fitted properly.
Suitability of the cargo
It is unfortunately very often the case that large heavy equipment is presented for sea transportation where the equipment designer has no understanding of the forces that will be imposed upon the item when it is on a ship at sea. Ideally, a sea transportation load case would have been considered at the design stage and the cargo can be demonstrably proven to have sufficient integral strength to withstand the forces that will be imposed on it in a seaway and will be provided with adequate strong points to which lashings of sea fastenings can be attached. It is not always obvious how it is intended that project cargoes are secured on a ship. For example, pressure vessels may be clad in insulation with no attachment points for lashings, or shipped on cradles that are suitable for vertical static loads ashore but have not been designed for the rigours of sea transportation. Lifting lugs may be badly positioned or in the incorrect orientation for use as attachment points for lashings. Special finishes or materials to which sea fastenings cannot be welded or chain lashings attached may also be an issue. Heavy machinery may be protected by timber packing which covers up suitable lashing attachment points (and it is of little use securing the timber encasing the cargo if the heavy cargo moves within the packing). If heavy cargo is presented for shipping on wheeled trailers, care must be taken to ensure that both the cargo and the trailers are secured. Do not assume that the cargo has been adequately secured to the trailer. If it is not obvious how to go about securing the cargo, advice should be sought from the shippers. If the structural integrity of the cargo is dependent upon how it is supported and secured on board, then specialist assistance must always be sought, preferably before the cargo is even accepted for shipment.
The chartered ship must be suitable for the cargo to be transported with respect to the space requirement, structural strength and stability. These matters are all interdependent and should be considered together. Whether stowed on deck or below, there needs to be sufficient space around all the cargo to fit the lashing or sea fastenings. The ship’s structural strength needs to be considered at an early stage to ensure that the ship is capable of carrying the cargo at all and that the location being considered has adequate local strength. Cargoes which are sensitive to environmental exposure may need to be stowed in the hold. Cargoes stowed on the deck should be located where they do not interfere with the normal operation of the ship or contravene the bridge visibility requirements. Special consideration will need to be given where the cargo is likely to be exposed to significant forces from green seas. Normally, cargoes should not be allowed to overhang the sides of a ship. Where this is necessary, special consideration will need to be given to both forces from green seas and possible uplift buoyancy forces if ship motions and passing wave crests are likely to result in the partial immersion of the cargo. The location of the cargo will affect the ship’s stability and the ship’s stability will affect the forces on the cargo and possibly dictate a suitable stowage location.
In planning the overall stow, the first consideration will always be cargo positioning to utilise space most efficiently along with the overall global strength of the tank top, deck or hatch on which the cargo is to be placed. Access, crane capacity and crane outreach or room to manoeuvre trailers will also be considered. With heavy cargoes, it is usually not sufficient to rely solely upon the overall load-bearing capacity of the tank top, deck or hatch (the permitted tonnes per square meter). The cargo must be positioned and supported over the strong points of the deck beneath the cargo. This will require consideration of the supporting points beneath the cargo, the ship’s supporting structural members and the exact position the cargo will be located, whilst complying with any limitations imposed by the overall stow plan. The overall position of the cargo should provide sufficient space around the cargo (to adjacent cargo, ship’s structure or a deck or hatch edge) to fit the proposed lashings or sea fastenings. There needs to be room for the lashing/sea fastening itself and room to install it. Unless new lashing points or sea fastening are to be welded to the ship, the cargo must be positioned so that the existing lashing points are both sufficient in number and appropriately positioned for the proposed lashing arrangement. It is, of course, preferable that full details of the cargo are known in advance to allow proper planning, although this is not always possible.
Calculation of the forces
As soon as the approximate location of the cargo is known, the forces on the cargo should be determined. These forces comprise the static weight of the cargo plus the dynamic forces from the six degrees of vessel motion discussed above. The forces are required in order to plan the lashings or sea fastening arrangement and determine the vertical forces on the supporting ship’s structure. The forces on the cargo should be calculated in accordance with the CSS Code. Whilst the CSS Code remains the default methodology for determining forces on the cargo, other methods (usually based on more rigorous engineering principles) may be proposed by the shippers or their surveyors (based on classification society rules or a marine warranty code of practice, for example). The calculation will consider the characteristics of the ship, the location of the cargo within the ship and the mass of the cargo. The calculated overall forces on the cargo must be applied at the centre of gravity of the cargo to determine the vertical forces on the support points, the lateral and transverse forces and overturning or tipping moment (if any) and the resultant forces at the lashings or sea fastening. If the centre of gravity of the cargo is unknown, it must be estimated using conservative values.
Once the forces on the cargo have been calculated, the loads exerted on the ship’s structure can be determined. The general positioning of the cargo can be verified with respect to the tank top, deck or hatch capacity and consideration then given to the exact location of the cargo and how the vertical forces from the cargo support will be spread into the supporting ship’s structure below. The location of the supporting structural members can be determined from the ship’s drawings, observation (from beneath the deck or hatch) and detected by ‘tapping’ the deck with a hammer to identify the precise location of the transverse and longitudinal stiffeners beneath. The overall loadbearing capacity of the deck and permitted linear loads on longitudinal stiffeners and girders and transverse frames, or point loads at transverse/ longitudinal cruciform may be annotated on the ship’s drawings. If there is any doubt that the structure is sufficiently strong to support the cargo transportation loads, specialist naval architecture help will be required. Heavy cargoes that have a small number of supports in fixed locations can present particular problems with respect to positioning over the supporting ship’s structural members. For example, typically, pressure vessels or wind farm components may be supported on two or more cradles at fixed locations. PAUs or machinery skids may be supported on feet (which will be bolted onto concrete foundation supports when installed in the plant or factory to which they are being shipped). Whilst one cradle or foot may be positioned over the supporting ship’s structure, the second or third support may not be coincident and will not align with the ship’s structure beneath (unless by some unlikely coincidence they both have the same spacing). Adjustment of the cargo position may be necessary to get the cargo support points over the ship’s structural members as intended. Ideally, transverse supports on the cargo should span the longitudinal structure on the ship or vice versa. If a compromise position, with the cargo, supports substantially over the supporting ship’s structure, cannot be achieved, it may be necessary to support a heavy cargo on a purpose-designed grillage. Unless this has been anticipated, properly designed and the appropriate materials and labour planned in advance, a satisfactory safe solution can be difficult to achieve at the time of loading.
Dunnage is traditionally used for the stowage of breakbulk cargoes to divide different cargoes or raise the cargo above the tank top. Its use for heavy cargoes should be for limited purposes only. Dunnage can be used to prevent metal-to-metal contact (between the cargo and the ship or grillage or between the cargo and the face of sea fastening stoppers). This increases friction between the cargo and the surface on which it is stowed and can protect the surface finish on the cargo. Dunnage can also be used to even out the contact between the cargo stowed on an uneven deck, ensuring that loads are transmitted into the ship’s structure at the location intended. Dunnage cannot be used as a construction material to support cargo, spanning between the ship’s structural members. This is the role of a properly designed grillage beam. Generally, thinner ply or dunnage timbers are preferable. Thicker sections of timber may crush under heavy cargoes which may then move causing lashings to go slack or sea fastening stoppers to misalign from the cargo up against which they should be closely butted.
Lashings and sea fastenings
Broadly, heavy cargoes can be secured by lashings (wires, chains or cargo straps) or sea fastenings (purpose-designed steel members that are welded or otherwise rigidly fixed to the ship and may be welded or similarly rigidly fixed to the cargo). Lashings and sea fastenings are considered separately below:
Lashings comprise all types of flexible securing arrangements, including all forms of binding chains, wires, cargo straps and the fittings required to secure and tighten them (senhouse slips, bulldog grips, cam buckles, ratchet mechanisms, bottle screws, shackles etc.). The MSL of the lashing is that of the weakest component. All fittings must be used correctly (e.g. shackles, padeyes and lashing points used in the correct direction of pull, bulldog grips orientated the correct way around and sufficient in number for the diameter of the wire, cargo straps used per the manufacturer’s instructions etc.). Wires and cargo straps must not be led over sharp edges or around radii smaller than that appropriate for the wire diameter. The number, orientation and MSL of the lashings must always be sufficient to restrain the cargo against the calculated forces within the constraints of the available lashing points on the cargo and the fittings on the ship. If sufficient lashing points on the ship or cargo are not available, either additional points should be provided (by welding new fittings in place if necessary) or the initial planning was incorrect and the cargo will need to be re-positioned. Restraint forces in each principal direction – transverse, longitudinal and vertical (to prevent overturning or tipping) must be calculated considering the lashing angles. For efficiency, the lashings should be at a shallow compound angle from the direction of the required restraint, as required by the CSS Code. It is important not to use more than one type of lashing in any one restraint direction. Using materials of different stiffness will result in the stiffest material carrying a greater load whilst the more elastic material will shirk load. For example, mixing chains and wires together will result in the stiff chain picking up load rapidly whilst the wire will stretch and carry less load. This risks the chain becoming overloaded and may result in the lashings breaking sequentially as the stiffer elements of the lashing become overloaded first.
The term ‘sea fastenings’ is usually reserved for steel components that are welded in place, although in some circumstances they may be bolted or clamped. They are usually designed specifically for the cargo and generally require more detailed planning and preparation before the cargo is loaded. Consideration will need to be given to ‘no weld’ areas both on the ship (in way of fuel tanks or insulated or coated bulkheads) and on the cargo itself. The least sophisticated form of sea fastenings comprises simple stoppers or clips welded to the deck. These butt up to the bottom of the cargo or clip over lower members of the cargo. They are generally not welded to the cargo itself and may require shimming with a thin steel plate to ensure full contact with the cargo or packing with thin pieces of wood to protect the cargo from metal-to-metal contact. The advantages of stoppers and clips are that they are easy to design and install, they do not require welding to the cargo (and thus leave it undamaged), and they can be designed to work mostly in shear (minimizing tensile, compressive and bending forces into the ship’s structure) and they require minimal pre-planning. Clips or stoppers are also generally easy to repair or reinforce should any problems be encountered during the voyage. More complex sea fastening designs may comprise combinations of large brackets and braces welded to both the ship and the cargo, and will generally be bespoke designs. Complex sea fastenings will be designed by a naval architect or structural engineer to an acceptable structural code to fit both the cargo and the structural arrangements of the ship. In general, all sea fastenings should be aligned with the ship’s structural members. If the forces are high, check calculations on the ship’s structure in way of the sea fastening (and/or grillages) will be required. Welded sea fastenings should not normally be mixed with lashings because of the extreme difference in stiffness between a ‘rigid’ welded sea fastening and an ‘elastic’ lashing. This will result in the problem of a very uneven load sharing more extreme than that which occurs with the use of disparate lashing materials, as described above. This does not preclude welded stoppers to restrain transverse forces from being used in combination with near vertical wires to restrain tipping moments. All welded sea fastenings should be constructed from traceable materials of known quality and fabricated by coded welders to an acceptable standard. Welds should all be free from visual defects and an agreed percentage of the welds should be inspected by an appropriate method of NDT (dye penetrant, MPI or UT). Wood is occasionally used as a sea fastening material, usually as shores between the cargo and a hold bulkhead. Generally, softwood is not suitable for heavy cargoes since it will crush and eventually work loose and become displaced. Greenheart high-density constructional timbers are strongly preferred for this purpose. Substantial engineering timbers may sometimes be used in lieu of a steel grillage to spread a heavy load across a short span between the ship’s structural members.
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Source: London Pandi