Đang tải... (xem toàn văn)
Shipowners accepting containers loaded with coils for transport to Colombia would, if the rolls of sheet steel were shipped in coil containers, also have to take a large number of emp[r]
(1)1.1 The history of the container
In May 2001, Malcolm P McLean, the "Father of Containerization", died aged 87 He used to say that he had the idea of rationalizing goods transport by avoiding the constant loading and unloading from one means of
transport to another way back at the end of the 1930s at the port of Hoboken, when still operating as a small-scale hauler To start with, McLean would load complete trucks onto ships, in order to transport them as close as possible to their destination The development of standardized containers and trailers, moved by tractors, made it possible to ship just the trailers with the containers, so saving on space and costs Later, the trailers were also left behind and the ships transported just the containers
Shipowners were more than a little skeptical about McLean's idea This prompted him to become a shipowner himself and he appropriately named his company Sea-Land Inc At the end of the 1990s, McLean sold his company to the Maersk shipping company, but his company name lives on in the name Maersk Sealand
In the literature, the "Ideal X" is mentioned as the first container freighter This ship left Newark on 26th April 1956 carrying 58 containers, which it transported to Houston The first ship designed to carry only containers is the "Maxton", a converted tanker, which could carry 60 containers as deck cargo That was in 1956
Another decade passed before the first container ship moored in Europe The first container on German soil was set down by the "Fairland" at Bremer Überseehafen on 6th May 1966 The first containers used by SeaLand in Northern Europe were 35' ASA containers, i.e they were constructed to American standards In other regions, 27' ASA containers and other ASA dimensions were often used Shipowners in Europe and Japan quickly recognized the advantages of the container and also invested in the new transport technology Since American standards could only be applied with difficulty to conditions in Europe and other countries, an agreement was eventually reached with the Americans after painstaking negotiations The resulting ISO standards provided for lengths of 10', 20', 30' and 40' The width was fixed at 8' and the height at 8' and 8'6" For land transport within Europe, agreement was reached on a 2.50 m wide inland container, which is mainly used in combined road/rail transport operations The majority of containers used worldwide today comply with the ISO standard, with 20'- and 40'-long containers predominating For some years, the ISO standard has come repeatedly under pressure As stowage factors increase for most goods, many forwarders want longer, wider and higher containers, preferably all at once Some shipowners have given in to the pressure and containers of dimensions larger than provided for by the ISO standard are now encountered distinctly more frequently "Jumbo" containers of 45' and 48' in length, widths of 8'6" (2.60 m) and heights of 9'6" (2.90m) have been in existence for some years Efforts to build even larger containers, e.g 24' (7.43m) and 49' (14.40m) boxes 2.60 m wide and 2.90 m high, are mostly confined to the USA Even 53' long containers have been in use for some time throughout the USA, while some states will even allow 57' In Europe and on other continents, narrower roads are a limiting factor
Developing countries are understandably against changing the standards More details are given in the section entitled "Container dimensions and weights"
1.2 Container flows
The huge investments made in containerization have paid off and container traffic is still continuing to grow Although growth will not be as unbridled as in the past, it will continue until all conventional transport operations have, within a container's limits of capacity and weight, been containerized
By then, it is estimated that there will be some 8000 ships in operation with a total slot capacity of nine to ten million standard containers There will be approximately the same number of containers ashore being packed or unpacked, awaiting stuffing or unstuffing or being transferred The majority of these containers are standard 20 foot box containers While there are special containers for many applications, growth rates for these are not significant
From the standpoint of container traffic, it would be ideal for there to be a balance between incoming and outgoing containers in a particular region, not only in terms of numbers, but also in terms of container type and weight Unfortunately, such a balance is not achievable There will thus always be empty containers to be transported in one direction or another From the shipping company's standpoint, general purpose containers usable in any circumstances would be a major advantage Forwarders, on the other hand, would prefer special containers if they could be carried at identical cost, as packing and securing is much easier in a special container than in a standard container
For example, steel sheet in coils can very quickly be loaded onto coil containers and straightforwardly secured They are rather more difficult to pack and secure on flatracks, while they are particularly difficult to pack and secure in box containers Shipowners accepting containers loaded with coils for transport to Colombia would, if the rolls of sheet steel were shipped in coil containers, also have to take a large number of empty standard ventilated containers to Colombia in order to transport coffee from Colombia to Europe Moreover, the coil containers, which are of no further use in Colombia, would have to be transported empty to somewhere where they could be used again As a result, steel sheet in coils will be transported to Colombia in "coffee containers" which are less suitable for carrying such cargoes
(2)
are placed inside normal standard box containers, the walls of which are frequently damaged by surging of the liquid in the flexitanks
A further example: experience has shown that containers exported from Europe to East Asia are, on average, heavier than those imported from East Asia In order to be able to carry the same weight of cargo in containers in both directions, empty containers have to be transported out to East Asia If many 40 foot containers are required to carry "light" cargoes from East Asia to Europe, it is sensible also to use these containers in Europe to carry "heavy" cargoes to East Asia Users of these containers get plenty of transport space, which is not actually required, plus a "securing problem" because such containers cannot be tightly packed
The majority of the world's container stocks are owned by shipping companies Quite a few are, however, leased in both large and small numbers to shipowners or other interested parties by leasing companies Some
forwarders ship goods in their own containers, but these are generally special containers for bulk cargoes, tank containers for chemicals or beverages or coil containers for the steel industry etc
1.3.1.1 Container-carrying vessels, part
Foreword
Anyone using containers for maritime transport should have at least some kind of idea of what kinds of vessels are used for this purpose When people who are not shipping professionals read press articles about gigantic new container ships, they find it hard to imagine that such ships could experience problems at sea It is very often also forgotten that even containers which have been carried for the vast majority of their voyage on ultra-modern ships will have to be carried for the remainder of their voyage, quite possibly highly adventurously, on very different kinds of ships This section of the Container Handbook is thus intended to provide an overview of the different kinds of ships which may be used to carry containers Reference should be made to the appropriate specialist literature if detailed information is wanted or required
Ships - general
Ships may be distinguished on the basis of various different criteria, for example by type of propulsion;
region of service;
function;
tonnage or measurement;
arrangement of decks or superstructures etc
Type of propulsion will not be a major concern for most maritime shipping customers In most cases, users will assume that the goods will be carried by motor or turbine ships The following and similar abbreviations are often found in the shipping documents prefixing the ship's designation: MS = motor ship; TS = turbine ship; CMV = container motor vessel; CTV = container turbine vessel However, it is still good to know whether containers will be carried onwards with other vessels, perhaps even sailing ships or open flatboats This is not uncommon in some parts of the world, for example in the Indonesian archipelago
Differentiation by region of service is often clear simply from the ship's name Examples are lakers (for use on the Great Lakes and St Lawrence Seaway), coasters (for coastal shipping), European inland waterway vessels, ocean-going vessels etc For shipping professionals, the name is enough to give them a picture of the nature and appearance of the ship and how it accommodates cargo etc
A ship's function is also generally reflected in its name, for example underwater vehicle, fishing vessel, tugboat, buoy-laying vessel, warship or the like As their name would suggest, feeder ships, for example, carry goods for onward carriage by other ships
Classification by tonnage, measurement, arrangement of superstructures etc is generally only of interest to the specialist Laypeople will be largely unconcerned whether goods are being carried on a full scantling, open-deck, shelter-deck or flush-deck vessel, a three-island or any other kind of vessel, although knowing the kind of vessel makes it possible to draw important conclusions about the type of carriage, transport risks, handling stresses etc
(3)
certainly does no harm to know that the ship's displacement or displacement tonnage is its total weight, i.e the sum of the weight of the empty, operational ship plus all permitted payload
This section of the Container Handbook will now outline some essential distinguishing features of those merchant ships which carry containers and comparable "combined transport units" Press articles often refer to the "type of freight" in this connection, but strictly speaking this is incorrect as freight is the amount of money the shipowner or carrier receives for transporting the cargo
Before taking a closer look at various types of ship, a breakdown by handling method may be helpful:
Breakdown by handling method
Lo-lo stands for lift-on/lift-off The cargo is lifted in and out of the ship (loaded and unloaded) using on-board
lifting gear or loading gear, such as derricks, on-board cranes or gantries, or also on-shore lifting gear This is the traditional handling method and is used for most ships throughout the world
Ro-ro stands for roll-on/roll-off, meaning that the cargo is moved on and off the ship on wheels This is achieved in various different ways Loaded trucks drive on/off ship under their own power, the driver either traveling with the truck and continuing onward carriage or leaving the truck to continue its journey
unaccompanied In either case door-to-door transport is possible Trailers or chassis are driven on board with special terminal tractors Roll trailers are packed at the port of departure, hauled on board with special ro-ro tractors, hauled off at the port of destination and unpacked there A similar situation applies to cassettes or
container bolsters packed in port, which are lifted up with special terminal vehicles and rolled on board and back off again This method covers all types of ship involved, for example, in ferry traffic Containers and swap-bodies are here (virtually) exclusively embarked and disembarked on roll trailers, chassis and similar means
Sto-ro stands for stow and roll In this case, the cargo is rolled on or off ship using one of the above methods, but is conventionally stowed when on board, usually by means of forklift trucks This method is not used for container traffic
Flo-flo stands for float-on/float-off Other variants are possible Floating goods or goods loaded onto floating cargo carriers are floated in and out of dock-like holds in the ship Alternatively, the carrier vessel
semisubmerges, moves under the cargo, refloats and lifts the cargo into the predetermined stowage space The cargo is unloaded by performing the process in reverse This method may be used for container transport if floating cargo carriers, such as barges, have already been loaded with containers
In the truck-to-truck method, the cargo is set down using ground conveyors, such as forklift trucks, onto on-board lifts, raised/lowered to the appropriate loading level, where it is loaded using ground conveyors Discharge proceeds in the reverse order This method is not suitable for container traffic
In the lift-and-roll method, the cargo is lifted on board with on-board loading gear or winch platforms and then rolled into place This method is preferably used with a special type of barge carrier This method is suitable for container traffic if the containers have previously been loaded onto or into the barges
Wo-wo or walk-on/walk-off sounds comical, but is in fact the commonest handling method for livestock carriers The animals walk onto and off the ship The same principle applies to all passenger vessels
(4)
Overview of merchant ship types
The above list is not exhaustive, but does give a relatively good overview of common types of merchant vessel In many ships, there is some overlap between the various options for carrying goods and the vessels cannot be assigned as strictly to one category or another as the list might suggest There have always been many different kinds of vessel, but recent years have seen the introduction of many more There is an unmistakable trend towards multipurpose ships This makes it difficult to make general statements about what ships look like and how they are equipped
Ships virtually always exhibit individual differences Even sister and standard type vessels are not identical in every respect In terms of naval architecture, there are no problems finding suitable vessels for cargo transport operations Organizationally, however, it is more difficult to find the correct ship It may be that certain vessels only serve specific ports or that certain cargos can only be carried in ships of a particular nationality One major issue is the increasing lack of skilled crews and stevedores in some parts of the world In relation to container shipping, ro-ro and ferry traffic, packing and securing in and on cargo transport units is a significant problem Non-seafarers underestimate the hazards of maritime transport and so for the most part pack and secure cargoes inadequately
The following paragraphs contain some comments on a selection from the huge range of different ships which may be of interest to container importers and exporters General cargo ships are only included to the extent that they also carry containers in many regions For the most part, the many different kinds of vessels will be
described only briefly
At the beginnings of container traffic, most containers were carried on conventional general cargo vessels
General cargo ship
(5)
tanks
General cargo ships of this old design are no longer being built, but many are still in use throughout the world The seakeeping ability of most such vessels at sea, low stowage heights and the like generally mean that carriage is safe and loss-free if individual containers are located in favorable stowage spaces and carefully secured Further information in this connection is provided in the shipping stresses section
Modern general cargo ships are built to perform different transport functions; to distinguish them from other multipurpose freighters, they are sometimes known as break-bulk freighters In addition to the equipment which makes them suitable for carrying break-bulk cargoes, they generally also have facilities to allow them to
accommodate containers Such ships are of open construction, i.e the hatch area is very large relative to the deck area This ensures that lifting gear can gain direct access to containers The same applies to general cargo or access is at least facilitated to such an extent that below deck stowage can (very largely) be avoided Specific construction features may increase handling efficiency in port and reduce the loss ratio
Multipurpose container vessel
Semi-container vessels are suitable for carrying both normal general cargo and containers Hold dimensions, deck loading values, the load-carrying capacity of the loading gear etc are tailored to the carriage of standard shipping containers Such vessels have 'tween decks generally with flush-closing mechanical hatch covers
Semi-container vessel
All-container ships are in principle of open construction as it must be possible to gain direct access to each container with lifting gear such as top spreaders and similar gear In order to obtain smooth, squared holds, these vessels are often constructed with a double hull Any holds which are unsuitable for carrying containers are often fitted out as tanks There are no 'tween decks All-container ships primarily carry containers and are specially equipped for this purpose
If the ports of the region of service are equipped with sufficiently powerful lifting gear, container ships are generally operated without loading gear In other regions of service, container ships too need loading gear in the form of derricks, cranes or gantries
Particular attention must be paid to the hydrodynamic design of container ships which operate at high cruising speeds The tall, heavy deck loads cause problems with righting capacity In order to ensure adequate stability, most all-container ships thus have to carry special solid or liquid ballast and/or be broader amidships The capsize risk of the vessels can be kept within acceptable limits by high values of the roll moment of inertia Large ballast capacities and high power pumps are absolutely essential, both for trimming the ships and for offsetting longitudinal bending moments Shipbuilders can tailor characteristics by selecting appropriate ratios between length, beam, molded depth, draft and other dimensions
The deadweight and hold capacity of container ships may also be stated in metric tons and cubic meters The number of available slots for 20' or 40' containers, however, is more meaningful TEU means "Twenty foot Equivalent Unit", while FEU means "Forty foot Equivalent Unit"
(6)
The VDI Guidelines recommend using the lowest value for the sliding friction coefficient μ if in any doubt In addition, attention is drawn to the fact that additional material pairs and environmental influences, such as dirt and ice, require that the friction coefficients should be estimated or should be determined specifically by testing
The following table gives sliding friction coefficients from the VDI guideline expressed as fractions, as gradients in % and as angles:
Table 2b - Sliding friction coefficients in accordance with the VDI Guidelines
Material Dry Wet Greasy
Wood on wood 1/5 through 1/2 20% through 50% 11.3° through 26.6° 1/5 through 1/4 20% through 25% 11.3° through 14° 3/10 through 1/20 15% through 5% 8.5° through 2.86° Metal on wood 1/5 through
1/2 20% through 50% 11.3° through 26.6° 1/5 through 1/4 20% through 25% 11.3° through 14° 1/10 through 1/50 10% through 2% 5.7° through 1.15° Metal on metal 1/10 through
1/4 10% through 25% 5.7° through 14° 1/10 through 1/5 10% through 20% 5.7° through 11.3° 1/10 through 1/100 10% through 1% 5.7° through 0.57°
Here it should be noted that the issue of friction is under review by the Verein Deutscher Ingenieure and the figures given above are now obsolete (information as at the beginning of 2002)
Rolling friction coefficients are much lower than static or sliding friction coefficients Values for common materials are shown in the following table:
Table - Rolling friction coefficients of selected materials
Material pairs Friction coefficient μ as Overflow
angle Surfaces in contact or bulk cargo Decimal Fraction Gradient
Roundwood, rollers and wheels on an unmade surface 0.5 1/2 50% 26.6°
Roundwood on rough surface 0.2 1/5 20% 11.3°
Roundwood on asphalt, steel or other firm surface 0.1 1/10 10% 5.7° Wheels with air-filled tires on a firm surface 0.02 1/50 2% 1.15° Steel wheels traveling on rails with flanged wheel grooves,
starting and shunting on free tracks 0.01 1/100 1% 0.57°
Railroad wheels on track rails, or clean flanged wheel grooves 0.0025 1/400 0.25% 2.5‰ 0.14°
Squared lumber with a square cross-section can act like rollers This risk is particularly high when using waney edge squared lumber since this often behaves in a similar way to roundwood
Never stand rectangular beams on edge Rectangular formats or, better, planks should be used flat The thickness should be calculated in order to ensure that lifting gear or ground conveyors are able to handle the goods A better format is the so-called "sandwich" which combines wood with top-quality friction-enhancing mats glued or screwed to each side The gluing or screwing can be made more durable if the lumber is shaped to accommodate the mats The depth should be measured in such a way that even when a heavy load is placed on the mat, the FE material is not crushed to such an extent that the goods are resting on the wood
(7)Incorrect, and incorrectly used lumber dunnage
If transport jolts are to be expected transversely to the orientation in which they are laid, rectangular formats such as planks are to be used It would be better to set out the beams parallel to the expected direction of the jolts, but for handling reasons, this is only rarely possible:
Risk of rolling with incorrect and correct use of wooden dunnage
As has already been mentioned, frictional forces can be reduced to zero as a result of vibration A certain minimum amount of load securing should always be implemented to counteract the effects of vibrations Goods should never be transported unsecured just because the calculated or assumed friction coefficients are greater than the horizontal acceleration that is to be expected With very few exceptions, for example, when materials are not compatible or the selected handling methods not permit the use of friction enhancing mats, friction should always be enhanced as much as possible by selecting the appropriate materials Since the use of tensioning or lashing aids or vertical bracing creates additional frictional forces, the load securing outlay may be reduced considerably if high friction coefficients can be achieved