A MASTER’S GUIDE TO: CONTAINER SECURING / container securing / NNPC CONTENTS
01 Voorwoord / Introduction 3
02 Basic advice 4
03 Do’s and don’ts 7
04 Lashing systems 9
05 Safe working 12
06 Ships 15
07 Containers 21
08 Container construction 26
09 Lashing components 31
10 Principles of stowage 36
11 Ship’s behaviour 46
12 Consequences of failure 51 voorwoord / introduction / 01 voorwoord
De NNPC heeft zich ten doel gesteld haar loss prevention beleid aan te scherpen. Een van de onderdelen van dit beleid is het beter informeren van leden over specifieke loss prevention onderwerpen om hiermee schadeclaims te voorkomen. De herverzekeraars waar de NNPC nauw mee samenwerkt beschikken over een reeks aan loss prevention publicaties die ook voor NNPC leden relevant zijn. De NNPC heeft van The Standard P&I Club de rechten verkregen om hun publicaties ook aan NNPC leden aan te bieden. We hebben er voor gekozen, gezien de Engelse terminologie die in de praktijk vaak wordt toegepast, de publicaties vooralsnog in het Engels aan te bieden en niet te vertalen naar het Nederlands. De eerste NNPC Master’s guide die we publiceren heeft als onderwerp Container Securing. Het doel van deze Master’s guide is de do’s en don’ts bij de bevestiging van containers aan de orde te stellen en het geven van adviezen om hiermee schades terug te brengen dan wel te voorkomen. Het streven is dat er op termijn meer publicaties gaan volgen.
Foreword
An improved policy on loss prevention is one of the objectives NNPC has decided to aim for. This includes providing better information to members about specific loss prevention topics in order to avoid claims. The reinsurers with whom NNPC has a close working relationship have published a great deal of information on loss prevention that is also relevant to NNPC members. Having acquired the rights from The Standard P&I Club, NNPC is now in a position to offer these publications to its members. As English terminology is quite common in our industry we have decided to make the original English documents available instead of having them translated into Dutch. Our first NNPC Master’s Guide is all about Container Securing. It highlights the do’s and don’ts of container securing and offers tips and advice which will enable you to reduce or prevent loss. We intend to publish more Master’s Guides in due course.
NNPC, Expertise bv Gijs Lindenburg / container securing / NNPC 02 basic advice
There are certain actions that should always be taken to prevent containers from being damaged or lost overboard. The following steps are considered best practice.
Points to remember try to avoid isolated stacks of containers in holds or on deck. Where check stack weights before stowage. possible, load containers so they are It is important not to exceed allowable evenly distributed stack weights; otherwise failure of the corner posts of the containers stowed avoid loading heavy containers at the bottom of the stack is possible. above light containers and at the top If the stow is too heavy, the lashings of a stack, unless the stowage arrange- may have insufficient strength to hold ment is shown in the Cargo Securing the containers in place if bad weather Manual and the stowage is found is encountered satisfactory when checked using the approved loading computer never deviate from the approved lashing arrangements shown in the avoid carrying open frame Cargo Securing Manual, except to add containers in cargo holds unless additional lashings. Calculate forces specifically permitted in the Cargo using the approved loading computer Securing Manual
discuss the proposed loading keep your system of lashing simple, with stevedores to ensure that the using the highest rated components proposed loading does not compromise the ship’s lashing system, loading to assist the shore lashing gang, give requirements or stability them precise instructions as to how containers should be secured consult the Cargo Securing Manual before applying lashings examine containers for physical de- fects – check the corner posts carefully. if stack weights are high and bad The corner posts have to resist high weather is expected, then fit additional compression forces as a result of static lashings weights from containers stowed on top Basic Advice /
and from dynamic forces that occur remember that during ship rolling, when the ship rolls, heaves and pitches. forces on container corner posts can Containers with damaged corner posts be up to three times greater than the placed in the bottom of a stow are upright compression force. Weather likely to collapse. Reject damaged route in an attempt to avoid the worst containers of the meteorological systems or areas where high seas in winter are common. check that all cell guides are clear Check the specified limits of meta- of obstacles, are straight and are not centric height (GM) in the Cargo buckled Securing Manual and make sure this is not exceeded. If navigating in bad check that turnbuckles are fully weather, reduce speed, avoid beam tightened. Loose lashings will be seas and proceed with caution until the ineffective storm has passed
avoid using left-hand and right- try to avoid loading ‘high cube’ hand twistlocks on the same ship containers on deck in the first or second tier. Lashing rods are more regularly examine lashing compo- difficult to fit and special rods with nents, including ship fittings, for wear extension pieces are often needed. and defects. Replace worn or damaged Before loading identify where these lashing components. Repair worn containers are to be stowed. It may be or damaged ship fittings. Check all necessary to reposition them equipment, not just equipment in regular use. Keep turnbuckles and always consider personal safety twistlocks clean and well greased when accessing lashing positions and working with lashing equipment. This consider additional lashings if bad applies equally in port and at sea weather is expected
it is difficult to know when lashing components should be replaced. Few organisations are confident to issue ‘criteria for replacement’, which means that the ship’s owner or individual master will need to exercise judgement. If in doubt, replace the equipment. Give special attention to dovetail or sliding socket foundations / container securing / NNPC
Outboard containers with lashings to the bottom of second and third tier boxes do’s and don’ts / 03 Do’s and don’ts always regularly check lashings avoid stowing ‘high cube’ during the voyage, when safe containers in outboard reject a container that is to do so positions found to be overweight or is likely to give rise to the inspect and tighten la- avoid geographical areas permissible stack limits being shings before the onset of where conditions for para- exceeded bad weather. Pay particular metric rolling exist attention to forward and aft reject a buckled, twisted or areas, and where vibration look for indications of damaged container could cause turnbuckles to water leakage into the loosen container; look for indica- check that containers have tions of leakage from the a valid CSC plate take care when handling container container fittings, as they are arrange stowage so that heavy. Avoid dropping them use safety equipment containers do not need to be unloaded at a port other than stow loose lashing compo- fit removable fencing the designated discharge port nents, twistlocks and lashing before accessing lashing rods safely in designated positions regularly check lashing baskets or racks components for condition close gratings and covers and discard components that buy components that are after passing through appear worn or are damaged supported by a test certificate. The strength of equipment report faulty equipment, regularly check container without a test certificate may including damaged ladders, corner castings for wear at be unpredictable. Keep a fencing, lighting or safety the twistlock and lashing rod copy of the test certificate on rails securing points. This is espe- board cially important when fully report problematic work automatic twistlocks are used have more securing equip- arrangements and discuss ment than necessary lashing safety during safety inspect D rings, ring bolts, committee meetings. cell guides and sliding socket avoid extreme values of Feedback can help to make foundations for wear or GM, whether high or low ships safer damage before containers are loaded, and arrange for the make sure container doors necessary repairs are closed / / container securing / NNPC never use twistlocks for lifting stand or walk below containers except where the containers that are being twistlocks are specifically lifted. Twistlocks or other mix left-hand and right- approved for this purpose debris can sometimes fall hand twistlocks open containers after they work dangerously with apply fully automatic have been loaded. Closed containers. Never stand or twistlocks without first doors are a component of the climb onto them, or under or checking the manufacturer’s container’s strength between them instructions for use and the requirements in connect reefer containers drop or throw fittings, the ship’s Cargo Securing to damaged or broken especially twistlocks, from a Manual electrical sockets great height onto a steel deck or other hard surfaces use corroded or buckled load containers in a lashing rods con-bulker that requires use a mixture of fully fitting a buttress, unless the automatic, semi-automatic use twistlocks that are not buttress is already fitted and manual twistlocks in the certified same stowage lash to the top of a use improvised equipment container; always lash to remove the hatch cover to secure containers the bottom of the next tier stoppers before hatch cover wherever possible stowed containers have been load containers of a discharged non-standard length or width use a fully automatic except when the ship is twistlock to secure containers stand adjacent to container designed and equipped for when the container’s bottom stacks which are being loaded the carriage of these is exposed and it could be or unloaded. The container non-standard containers lifted by green seas may swing and hit you
overtighten lashing rods. apply lashings to the This can occur when lashing overhanging end of a 45-foot rods are tightened during container when the contai- ship rolling, because one side ner is stowed over a 40-foot of crossed lashings will be container. 45-foot containers less tight on the heeled side. are usually stowed aft of the Tightening ona roll can cause ship’s accommodation and over tightening. Lashing rods above the position where can also be overtightened lashing rods are applied. They when a very long metal bar is are therefore held in position used to tighten the turnbuckle with twistlocks Lashing systems – common false beliefs / 04 lashing systems common false beliefs
P&l club investigations into container losses indicate that a loss often occurs because an apparent weakness has not been identified. The following common false beliefs or assumptions are worth noting:
Once containers have been loaded Containers loaded on a pedestal and and secured, the stow remains in a a hatch cover do not suffer additional tight block and does not move loading Twistlock and sliding socket clearances A hatch cover is designed to move as will allow containers to move before the ship bends and flexes. A container the twistlocks engage. The clearance stowed on a pedestal, a fixed point, will permit movement of the stow. will attempt to resist hatch cover Wear inside the corner fitting can movement if also secured to a hatch cause additional movement. cover.
Containers can be stowed in any Lashing rods should be tightened as order and/or combination/mix of tight as possible weights In theory, excessive tightening of The most common mistake made when lashing rods will result in the rods stowing and lashing containers is to taking additional strain, which can load heavy containers over light or to cause rod failure when under load. load so that the maximum permissible stack weights are exceeded. Heavy False Extra lashings will always make on light can only be accepted when the stow safer specifically permitted in the Cargo Application of extra lashings can, Securing Manual. at times, make the stow very rigid, causing large forces to pass to Lashings applied from a lashing container-securing points and bridge behave in the same manner as causing them to fracture. those applied at the base of a stow A lashing bridge is a fixed structure It is not necessary to adjust the while a hatch cover will move when tension in lashings while at sea a ship rolls and pitches. The resulting Movement of containers will result effect could be that a lashing from a in some lashing rods becoming slack. lashing bridge becomes slack or takes Air temperature differences will cause excessive load. the tension in the lashings to change. 10 / container securing / NNPC
Lashings should be checked and However, the container will be held tightened within 24 hours after leaving rigidly to the fixed lashing bridge. port and regularly thereafter. This is When a ship bends and twists, the especially true before the onset of bad base of a container attached to a hatch weather. cover will move, but container ends held firmly to a lashing bridge with Container strength is equal horizontal lashings will not move. throughout the container The effect will be to put strain on the Although strength standards are met, lashings and even break the bars or a container is more flexible at the door damage the container corner castings. end and may be more vulnerable in Horizontal lashings should not be used this area. unless specifically permitted in the approved lashing plans shown in the All twistlocks can be used to lift Cargo Securing Manual. containers Twistlocks can be used for lifting Parametric rolling will not occur containers only when they have on ships with a high GM been approved and certified for that Parametric rolling occurs because purpose. False of the fine hull form of large post- Panamax container ships. The large Twistlocks are all rated to the bow flare and wide transom increase same strength the effect. The phenomenon occurs Twistlocks can be rated for different because of changes in the waterplane tensile loads up to 20 or 25 tonnes. area, which can cause large changes in It is important not to use a mix of GM as waves pass. At times, GM can twistlocks that have different strength become negative. A large initial GM ratings. will provide large righting levers that can lead to violent rolling. All containers have the same strength Provided stack weights have not Container strength can vary. There are been exceeded, the distribution of two ISO standards (pre- and post- containers in a stack on deck is not 1990). Some owners have their own important standards and containers can be worn It is essential to avoid loading heavy or damaged. containers over light, or at the top of a stack in a deck stow, unless specifi- Horizontal lashings from lashing cally permitted in the Cargo Securing bridges are an alternative to vertical Manual. This is because the securing cross lashings system would normally have been Crossed horizontal lashings from designed on the assumption that light lashing bridges will hold a container. containers are stowed on top. Stowage Lashing systems – common false beliefs / 11
may allow for ‘heavy-heavy-light’; however, loading ‘heavy-medium- medium’ may result in the same stack weight but would produce different strain on the securing system, especially if the GM is high.
Containers need not be stowed in block stowage Generally, container stacks do not depend on each other for support. However, they do provide protection to each other from wind and waves, so stowage in isolated stacks, especially in outboard locations, should be avoided. foto wim te brake te wim foto 12 / container securing / NNPC 05 SAfe working
working with containers when working on the top or side of a container, use safe access equipment The decks, hatch covers, lashing and never climb containers bridges and holds of a container ship can be hazardous places to work. To if working from a portable ladder avoid accidental injury, exercise care make sure the ladder is properly and follow these rules: secured, has non-slip feet so that metal-to-metal contact is avoided. when working on deck, always wear Wear a safety harness, a hard hat and high visibility clothing, safety shoes high visibility clothing. Attach the line and a hard hat from the harness to a secure point and arrange for a member of the ship’s always install temporary fencing crew to stand-by to assist and safety bars before starting cargo operations take care climbing onto a lashing bridge. There could be loose items of never allow fittings to be thrown equipment that can fall or the safety onto the ship’s deck from a height bar could be across the opening
check that sliding sockets and tidy loose equipment that is lying stacking cones are removed from hatch on decks, hatch covers, lashing bridges covers before opening and coamings. These are trip hazards
when working in the vicinity of never climb up a stack of containers. moving containers, never work with Use an access cradle your back towards a container or stand where a swinging container could take care when fixing penguin hooks strike you or lashing rods, as these can slip and strike someone never stand or walk under a raised container avoid excessive stretching, bending or leaning when placing lashing rods. never place your hand or clothing Their weight can be deceptive under a container that is being lowered close access gratings after passing through. They are there to protect you safe working / 13
Application of outboard lashings
Lashing areas Working areas must:
Ships should be arranged to enable avoid the necessity for or, where that is not safe application and inspection of container top working possible, temporary container lashings. Work areas should fencing be of adequate dimensions, free from be designed with the trip hazards, provided with fall work platform and have adequate protection and with adequate lashing plate on the lighting and non-slip lighting. Transit areas should be free same level surfaces from obstructions and trip hazards. They should have adequate headroom, be of adequate size have safe arrange- lighting and non-slip walkways. ments for stowage of The main working positions are be arranged to avoid spare lashing equipment between stacks, on lashing bridges, excessive stretching or outboard and on hatch cover ends. bending during lashing have access hatch A risk assessment of working positions application openings to raised should be arranged to identify hazards working areas closed by and to enable corrective action. When have outboard areas gratings rather than completing these assessments, the and potential falls solid covers following requirements for safety fitted with permanent during the application of lashings should be considered. 14 / container securing / NNPC
Potential falls from heights of 2m or Work areas and walkways, whether more need to be fitted with fall above or below deck or on a lashing protection in the form of fencing. bridge, require lighting. In work Fencing should have its top rail at areas, the level of lighting should be least 1m high and an intermediate rail sufficient to enable the inspection of should be fitted at a height of 0.5m. containers, both in port and at sea, Toe boards should be fitted where to detect damage and leakage, and to people below could be exposed to read markings or labels. falling objects.
Crew member checking lashings stowed athwartships ships / 15 06 ships
A ship is only designated as a container ship when it is designed exclusively for the carriage of containers. Other ship types that carry containers as part of a mixed cargo are often categorised as ‘suitable for the carriage of containers in holds xxx and x’.
P&l clubs provide cover for the carriage of containers on deck only when the ship is specifically designed, fitted or adapted for the trade. This means that hatch covers and container landing points are approved for the particular stack weight and the lashing system satisfies classification society design criteria.
Containers can be carried on many ship types – cellular container ships, con-bulkers, bulk carriers and general cargo ships. The following is a brief description of the ships and their features. 16 / container securing / NNPC ship types
Cellular container ship
container ships
designed exclusively for the carriage of containers containers in holds are secured by cell guides containers on deck are secured by portable lashing components, often rods and twistlocks ships / 17
Hatchcoverless container ships – container ship hatchcoverless
designed exclusively for the carriage of containers no hatch covers bridge may be located fully forward to provide protection if the bridge is not sited forward, it is common for the forward two or three holds to be fitted with hatch covers, especially if dangerous goods are to be carried all containers are secured in cell guides
Typical arrangement CON-bulkers for con-bulker with gantry crane a ship with hold arrangements suitable for the carriage of both containers and bulk cargoes various configurations, including: – bulk cargoes carried in designated holds, containers in other holds – containers carried above bulk cargo – containers carried only on deck 18 / container securing / NNPC
Ro-Ro cargo ship with ro-ro ships containers on deck various configurations, including: – Ro-Ro cargo aft and containers in conventional holds forward – containers loaded by forklift trucks in Ro-Ro decks – containers on deck and Ro-Ro cargo in the Ro-Ro deck
Multi-purpose general cargo ships general cargo ship with capacity to carry containers in holds, generally containers on deck secured by buttresses and bridge fittings containers on deck secured by container securing equipment containers may be carried athwartships. Only possible when cargo is carefully stowed within the container
containers loaded on dunnage and carried as general cargo ships / 19
Lloyd’s Register’s ‘Register of Ships’ and ‘Rules & Regulations for the Classification of Ships’.
ship classification
The ship classification process ensures Multi-purpose ships may carry that the ship’s hull, hatch covers, containers and general cargo. These lashing bridges, cell guides and fixed ships can be cellular container ships fittings have sufficient strength. Loose with a stiffened tanktop with the fittings such as container securing ability to ‘stopper’ (block) cell guides. components may be excluded from this certification process. Although a Sometimes owners wish to carry bulk classification society may assess the or general cargoes in container ships. adequacy of loose fittings and assign A ship which is classed as a container a class notation, this examination is ship will not have been assessed for additional to the mandatory ship this type of loading, nor will the inner classification process. bottom, hatch covers, loading manual, Cargo Securing Manual and ISM P&l clubs require a ship to be certification have been approved for approved for the carriage of containers the carriage of these cargoes. Before by a classification society and for the general cargo can safely be carried on container securing arrangements to at a container ship certification as a least meet that classification society’s general cargo ship is necessary. The design requirements. club has published an edition of Standard Cargo on the subject of container ships and general cargo. 20 / container securing / NNPC foto wim te brake containers / 21 07 containers
Most containers carried at sea are designed and approved to ISO standard and are regularly inspected in accordance with the International Convention for Safe Containers (CSC) for damage, to ensure that they continue to be suitable for the very large loads which they are required to bear while at sea. There are various types, sizes and designs of container. Not all are suitable to be part of a container stow. 22 / container securing / NNPC
container sizes Containers with stacking limitations (such as 5-high stack) have labels Containers are standardised cargo clearly marking these requirements. units. They are normally manufactured The stacking capability is also specified to the sizes specified in ISO 668, but on the CSC Plate. they can be manufactured in a variety of sizes and types, each designed to meet specific cargo and transportation requirements. Their length is usually 20 or 40 feet, although longer containers are used, principally in the US trade; these containers are 45, 48 and 53 feet long. Their width is standardised at 8 feet (2,438mm), although their height can vary. The term ‘high cube’ container usually refers to a standard sized container The usual value for allowable stacking that has a height of 9 feet 6 inches. is 192,000 kg, which is a 9-high stack Container heights can be 8 feet, 8 feet of containers, calculated as 8 containers 6 inches or 9 feet 6 inches. stacked above, each with a mass of 24,000kg (8x24,000=192,000). Containers are referred to by the acronym TEUs – 20 foot equivalent Containers that are longer than 40 feet units, or 40 foot equivalent units usually have additional support points (FEUs). at the 40-foot position so that they can be stowed over a standard 40-foot The ISO standard for containers (ISO container. Standard sizes for ISO Series 668) defines dimensions, both internal 1 freight containers include those and external, and load ratings. All shown in the table below. containers have a framework and corner posts fitted with corner castings. Twenty-foot containers are actually a The castings at each corner of the little shorter than 20 feet, so that two container support the container’s weight. 20-foot containers can be stowed in a 40-foot bay. The actual dimensions are The castings are the only points at 12,192mm for a 40-foot container and which a container should be supported 6,058mm for a 20-foot container. and are used to attach securing fittings, Thus, two 20-foot containers are 76mm such as lashing rods and twistlocks. shorter than a 40-foot container. This The position and spacing of corner clearance is often referred to as the castings are carefully controlled. ‘ISO gap’. containers / 23
Do not lash to the overhanging end of a 45-foot container
Standard sizes for ISO Series 1 Freight Containers
Designation Length Width Height 9’ 6” (non-ISO) 8’ 6” 45’ 8’
1AAA 9’ 6” 1AA 8’ 8’ 6’’ 40’ 1A 8’ 1AX < 8’ 1BBB 9’ 6’’ 1BB 8’ 6’’ 30’ 8’ 1B 8’ 1BX < 8’ 1CC 8’ 6’ 1C 20’ 8’ 8’ 1CX < 8’ 1D 8’ 10’ 8’ 1DX < 8’
Appro ximate dimensions, in feet and inches. Most common sizes highlighted. Suffix ‘x’ means the container height is less than 8 feet.
24 / container securing / NNPC
Container types
There are a number of types of Curtain wall containers container in common use. They all have basically the same frame, and the curtain wall containers are similar differences relate to what they can be to dry van boxes, but have fabric side used for and access. walls that can be opened to facilitate easy cargo handling Dry van boxes
these are the most common type they have corrugated steel walls, timber base, steel or glass reinforced plastic (GRP) top corrugated walls can be made from plate from as little as 1.6mm (1/16 inch) in thickness their frame consists of side and end rails, and corner pillars fitted with corner castings the closed end is approximately 4.5 times more stiff, in racking strength, Reefer unit than the door end closed doors are a component of their Refrigerated containers strength general construction as for dry van boxes they usually have their own refrigeration unit, with an air or water-cooled heat exchanger a small number of CONAIR boxes use close-coupled ventilation they have their own data logger to record temperature some have controlled atmosphere for the carriage of fruit
40-foot dry van box container containers / 25
Euro containers
Euro containers are 45-foot containers designed to comply with EU Directive 96/53 they have shaped corner castings to comply with road transportation regulations their cell guides need to be appro- Typical arrangement for a tank container priately designed to ensure that the containers cannot slip out of them Tank containers
steel skeletal framework within which the tank is housed steel framework must have equiva- lent strength to a dry van box the tank has its own design and strength criteria and it may be a pres- sure vessel if carrying ‘dangerous goods’ the tank container will also be certified to ADR/RID/IMDG
Flat-rack containers
the container frame can be folded flat for ease of transportation when empty the structure must have equivalent Corner casting arrangement for a strength to a dry van box Euro container
Two flat racks over stowed 26 / container securing / NNPC 08 container construction The strength of a container is provided principally by the outer framework, side rails and corner posts, together with the corner castings. The side, end panels and closed doors provide racking strength.
Corner posts provided by the frame and also by the plate walls. Of course, soft- Effective stacking of containers relies walled containers rely totally on the on the strength of the corner posts to racking strength of the frame. support the weight of the containers above. Damage to a corner post, in Corner castings particular buckling, can seriously degrade its compressive strength and A container’s corner castings take the lead to the collapse of a container twistlocks or stacking cones, which stack. are used to connect containers to each A series of tests is undertaken on a other or to the ship’s deck/hold, and prototype container to comply with the the lashing rods, which are used to Lloyd’s Register Container Certification secure and support the stow. During Scheme, the CSC and the applicable lifting, the crane’s spreader bar ISO standards. connects to the corner castings.
These tests simulate the different loads While compressive loads can be the container is likely to be subjected carried by the direct contact between to; an example of this in the photo the containers, tensile and shear loads above is a stacking test. are resisted by the loose fittings. It is important that the corner castings are The outer frame in good condition if the fittings are to work effectively and perform their Horizontal forces on the container, intended function. such as those caused by roll and pitch motions, are resisted by the racking The position of corner fittings must strength of the container. This is be carefully controlled during the container construction / 27
Container test rig manufacture of containers to ensure If tests prove satisfactory, then the that they fit together properly and container design may be certified by to ensure that the fittings work a classification society. effectively. It is important to note that a container Forklift pockets that has suffered damage to a corner casting or corner post will not be These can be cut into the bottom side serviceable because: rail and are used when the containers a damaged container may be unable are lifted by a forklift truck. Forklift to bear the weight of those stowed pockets are a discontinuity in the side above rail that could weaken the container if a damaged container may render contact damage occurs. lashings ineffective lifting a damaged container is Container certification hazardous
New designs of container are prototype If one container in a stack fails, it is tested to ensure that they have likely that the entire stack will sufficient strength. collapse. 28 / container securing / NNPC
container construction and faults
Certification containers, open top containers, non-pressurised dry bulk containers Certification is then issued by the and platform-based containers classification society for containers of Tank containers similar design, that are constructed Offshore containers by production methods and quality control procedures that are agreed and The scheme ensures that each contai- verified by survey. Changes in the ner complies with the appropriate ISO method of construction may nullify the standard and applicable regulations, certification, unless the changes are covering for example: approved by the classification society. dimensions strength of walls, floor and roof The Lloyd’s Register Container strength of corner posts Certification Scheme (LR-CCS) covers rigidity (longitudinal and transverse) three general categories of container: weathertightness number of other features as ISO Series 1 containers – all types, appropriate to the type of container, including: dry van boxes, reefer such as strength of forklift pockets container construction / 29
A container that has satisfactorily ISO 1161: Corner Fittings, passed the Lloyd’s Register Container Specification Certification Scheme will bear the ISO 1496-1: Specification and Lloyd’s Register logo. Testing. Part 1: General Cargo Containers for General Purposes ISO 1496-2: Specification and Testing. Part 2: Thermal Containers ISO 1496-3: Specification and Testing. Part 3: Tank Containers for Liquids, Gases and Pressurised Dry Bulk
International Convention for Safe Containers (CSC)
The CSC Convention sets out the When containers are strength tested, it standards for freight container is important to remember that they are construction and use. not tested for vertical tandem lifting The convention contains regulations and that the corner posts are only on construction, inspection, approval tested for compressive strength. In and certification. addition, it is only the top corner This includes design approval, witness fittings that are tested for lifting; of container manufacture and proto- the bottom fittings are never tested. type testing and issuance of a safety Twistlocks may be approved for plate. The CSC approval or safety plate vertical tandem lifting; however, such contains information on the contai- lifting is dangerous and should only ner’s date of manufacture, the manu- be contemplated when a container’s facturer’s identification number, the bottom corner castings are also gross operating weight, the allowable approved for lifting. If in doubt, stacking weight and the transverse rac- consult the ship’s P&I club. king load. The plate may also have the end and/or side-wall strength value. ISO Series 1 – Freight The plate is issued when the container Containers is manufactured.
The primary documents for the design In accordance with the CSC all con- of ISO Series 1 Freight Containers are: tainers shall be examined at intervals ISO 668: Classification Dimensions specified in the convention by one of and Ratings two ways: either by a ‘Periodic Exami- 30 / container securing / NNPC
nation Scheme’ or under an ‘Approved Continuous Examination Programme’ For example, 9 kW of electrical power (ACEP). Both procedures are intended is needed to maintain a temperature to ensure that the containers are of minus 18°C in a 40-foot container maintained to the required level of carrying frozen meat, while a container safety. The maximum period between carrying fruit at 2°C requires approxi- examinations is set at 30 months or if mately 11 kW. This is because fruit there is a major repair or modification respire and produce heat during and for the ACEP scheme for on hire/ transit. off hire interchanges. For tank contai- Certain cargoes, for example bananas, ners the ADR (Transport of Dangerous may require even more power because Goods by Road), RID (Transport of of the greater heat produced as they Dangerous Goods by Rail) and IMDG ripen. There is a high electrical load (Transport of Dangerous goods by on the ship’s generators when reefer Sea) also have in-service inspection containers are carried. requirements. The standard EN 12972 thoroughly Containers with open doors details these requirements. Some containers are certified for use Certification of reefer with one or both doors open, or remo- containers ved. This may be necessary to ventilate cargo. A note saying the container’s The ability of a reefer container to doors can be open will appear on the maintain a given temperature when CSC plate under the transverse racking using its integral refrigeration unit is entry. Unless a container is certified to tested in accordance with ISO 1496-2. have its doors open, the doors must This consists of two tests: one to be closed and secured – they are an determine the heat loss through the integral part of a container’s strength. envelope of the container and the other to ensure the refrigeration unit can operate with a specific internal load. These tests are arranged during type approval. The amount of electrical power required to maintain a reefer container at a given temperature depends on the size of the container (TEU or FEU), the required cargo temperature, the cargo being carried and the external ambient air temperature. lashing components / 31 09 lashing components A variety of lashing components are available to secure containers, the majority of which are listed below. The table shows the locations where these components are commonly used.
Fixed fitting (attached to ship)
Description Purpose Image Notes
Flush socket Locating base twistlocks Normally fitted over a or stacking cones in the small recess to ensure cargo hold. watertightness. Clean and remove debris before use.
Raised socket Locating base twistlocks Clean and remove debris or stacking cones on before use. deck.
Lashing plate or Tie-down point for Designed only for in- ‘Pad-eye’ turnbuckle. plane loading. An out-of- plane (out-of-line) load could bend the plate and may crack the connecting weld.
D ring Alternative tie-down Corrosion of the pin point for a turnbuckle. ends can weaken a D ring. Suitable for in-plane (in-line) and out-of-plane loading.
Dovetail foundation Base for sliding Clean before use. dovetail twistlock. Keep well greased and examine regularly for damage or wear.
32 / container securing / NNPC
Description Purpose Image Notes
Fixed stacking cone Locating base twistlocks Often found at the or stacking cones in the base of a cell guide. cargo hold.
Mid-bay guide To prevent transverse Does not interfere with movement of 20-foot general stowage of containers in 40-foot 40-footcontainers. guides. Fitted at tanktop level.
Loose fittings are those that are not surveyor during regular ship surveys. permanently attached to the ship. When using loose fittings, it is Loose fittings must be certified by essential that the manufacturer’s class or an appropriate recognised instructions are followed at all times, authority. However, they are not especially when using fully automatic normally surveyed by the class society and semi-automatic twistlocks.
Loose fittings in common use
Description Purpose Image Notes
Lashing rod To provide support Resists tensile loads. for container stacks Very long lashing rods on deck.Used in can be difficult to conjunction with a handle and difficult to turnbuckle. locate in a container corner casting. They can have eyes at each end.
Extension piece To extend a lashing rod Fit at the base of al when securing ‘high ashing rod and connect cube’ containers. to the turnbuckle.
Turn buckle (bottle To connect a lashing Resists tensile loads screw) rod to a lashing plate and is used to keep the or D ring. Tightening lashing tight. Regu- puts tension into a larly grease its threads. lashing rod. Ensure the locking nut or tab is locked. lashing components / 33
Description Purpose Image Notes
Hanging stacker Used in holds when Resists horizontal forces. 20-foot containers Likely to be put in place are carried in 40-foot when container is on guides. Locks into corner shore because of casting above. difficulty in fitting when on board.
Semi-automatict Placed between Resists horizontal and wistlock( SAT) containers in a stack. separation forces. Can Locks into corner be fittedonshore. Auto- castings above and matically locks into the below. lowercontainer when placed on top. It is easier to determine whether it is locked or not when compared to manual twistlocks. Unlocked manually.
Twistlock Placed between Resists horizontal and containers in a stack. separation forces. Each Locks into corner fitting requires locking castings above and after fitting. Left and below. right-hand types exist, causing uncertainty whether a fitting is locked or open.
Stacking cone Placed between Resists horizontal forces. containers in a stack. Many types exist. May Slots into corner be locked into bottom castings. corner castings prior to lifting a container on board.
Fully automatic Placed between A new and innovative twistlock (FAT) containers in a stack. design. Automatic Locks into container unlocking during lifting. casting above; hooks Usually opened by a into container casting vertical lift, with a below. twist/tilt. Should not be used if container corner castings are worn or damaged. 34 / container securing / NNPC
Description Purpose Image Notes
Mid-lock Placed between Resists horizontal and containers in a stack. separation forces. Locks into corner Fitted to underside of castings above and container on shore and below. Used on deck automatically locks into between 20-foot lower container when containers in 40-foot placed onboard. Con- bays, at mid-bay sult the manufacturer’s position. instruction manual for information on the lock’s correct direction of fitting.
Loose fittings in less common use
These fittings are not commonly used to the container top, something that but may be encountered occasionally. should be avoided unless absolutely Fitting a bridge piece requires access necessary.
Description Purpose Image Notes
Sliding dovetail To connect bottom Fits into a dovetail twistlock containers to the ship. foundation. Used on hatch covers and in holds where a raised socket could cause an obstruction.
Bridge fitting To link together the Resists tensile and top containers of two compressive forces. adjacent stacks. Can Potential drop hazard be used on deck or in for stevedores/crew a hold. during placement.
Buttress External support for Can resist compressive container stacks in a and tensile forces. hold. Must be used in conjunction with higher-strength double stacking cones or link plates and aligned with side support structure. lashing components / 35
Description Purpose Image Notes
Double stacking cone To link adjacent stacks, Resists horizontal particularly those in forces. More commonly line with buttresses. used on con-bulkers below deck.
Load equalising device To balance the load Enables two parallel between two paired lashing rods to be lashings. connected to a single turnbuckle. Only use with designated lashing rods.
Penguin hook Used as a supporting Likely to be put in device in conjunction place when container with a special lashing is on shore because rod with an eye-end. of difficulty in fitting when on board. Risk of injury if it falls out when container is lifted onboard.
Elongated socket Locating base twist- Enables movement locks or stacking cones between a hatch cover on deck. and container to be taken up.
assorted twistlocks 36 / container securing / NNPC 10 Principles of stowage Containers are rectangular box-shaped units of cargo. It is easy to stow them in classical block stowage both on and below deck.
When containers are carried on deck, Containers carried on deck may be the ship is required to be approved for secured by twistlocks alone, provided that purpose and the containers them- the stack is not more than two contai- selves are secured with twistlocks and ners high. When containers are carried lashings. These usually consist of steel three high, twistlocks alone may be rods and turnbuckles. sufficient depending on the weight of the containers. When containers are carried below deck, the containers are slotted into Horizontal movement of a deck stow cell guides on a cellular container ship, is resisted by the twistlocks or cones. or sit on the tanktop, joined together Lifting of containers in extreme seas with stacking cones, in the holds of a is prevented by the pull-out strength dry cargo ship. Containers can easily of the twistlocks. The limitation of a be stowed in box-shaped holds; it is twistlockonly stow is often the racking more difficult to carry them in the strength of the containers. For stows holds of a dry cargo ship fitted with of more than three containers high, side hopper tanks, in which case, lashing rods are fitted because they buttresses may be fitted. provide additional racking strength.
When carried within a cell guide In the early days of containerisation, framework, no further external support lashings were fitted vertically to resist is generally required. When 20-foot tipping. However, it soon became clear containers are stowed below deck in that it is more effective to arrange 40-foot cell guides, it may be beneficial the lashings diagonally, so that the to overstow the 20-foot containers container and the lashings work with a 40-foot container. The Cargo together to resist racking. Securing Manual should be consulted before loading. The usual arrangement is to fit one tier of lashings, placed diagonally within principles of stowage / 37
Securing with parallel lashing rods and semi-automatic twistlock
the width of the container, with the ship rolling, it is the lashing rods that tops of the lashing rods placed in bear the force first. It is only after the bottom corner castings of the the stack of containers has deflected secondtier containers. This is called and the gap at the twistlock has been ‘cross-lashing’. An alternative arrange- ‘taken up’ that twistlocks become tight. ment, with the lashing rods located For this reason, it is important to only outside of the width of the container, use lashing rods that are in good is called ‘external lashing’. This is often condition and to apply them correctly. used for high stacks which are lashed A second set of lashings may be fitted, from a two-tier lashing bridge. connected to the bottom of the third tier of containers, as shown in the To enable the fitting of twistlocks, a diagram. twistlock is designed with a vertical and horizontal gap between it and a If additional lashing strength is container’s corner casting. This becomes required, parallel lashings (para- important when considering how lashings) may be used. lashings behave during ship roll, pitch With this arrangement, lashings are and heave. Lashing rods are always arranged in parallel, one fitted to the fitted tight and kept tight by adjusting top of the first tier and one to the the turnbuckle. When force is trans- bottom of the second tier. Tests have mitted to securing equipment during revealed that many containers are not 38 / container securing / NNPC
able to bear large downward loads on Containers carried below deck the upper castings, as can occur with in cell guides para-lashings. This is particularly the case at the door end where the upper The cargo holds of most container casting frequently overhangs the door ships are designed for the carriage of and consequently has little support. 40-foot containers, with the containers The effectiveness of parallel lashings is held in place by cell guides. The cell taken as the lesser of 1.5 times that of guides are generally steel angle bars a single lashing or the strength of the orientated vertically, with entry guides corner casting. at the top to assist with locating the container – the clearances, and hence For ease of loading and discharge, construction tolerances, are very tight. bridge fittings that link adjacent stacks of containers together are not The cell guides provide adequate commonly fitted. However, since the longitudinal and transverse support to force distribution and the response the 40-foot containers and no further of adjacent container stacks will be securing arrangements are necessary. similar, there is, in general, negligible The lowest container in each stack sits load transfer between the stacks when on a pad, which is supported by the linked together. stiffened structure below the tanktop.
Bridge fittings tend to be used only on Twenty-foot containers may be stowed isolated adjacent stacks of containers in 40-foot bays. This arrangement, in the holds of a dry cargo ship. referred to as mixed stow, requires longitudinal and transverse support for The ship’s approved Cargo Securing the containers where they meet at the Manual contains information on how mid-length position. This is achieved to stow and secure containers, and on by mid-bay guides at the tanktop, any strength or stack weight limitations. placing hanging stackers between tiers of containers and possibly oversto- The most common mistakes made are wing two 20-foot containers with one to exceed the permissible stack weight, or more 40-foot containers. Isolated to incorrectly apply lashings and to stacks should be avoided. place heavy containers near the top of In general, four hanging stackers a stow. should be fitted below each container, unless the Cargo Securing Manual specifically permits a lesser number.
Before loading containers in cell gui- des, it is important to make sure that the guides are not bent or deformed. principles of stowage / 39
Typical arrangements for containers stowed below deck
40-foot containers in 40-foot cell guides
20-foot containers in 40-foot cell guides
20-foot containers in 40-foot cell guides with 40-foot containers stowed above 40 / container securing / NNPC
Various designs of portable buttress are available.
Aim for a tight block when loading containers below deck on a con-bulker. During loading, check to make sure that means are applied to ensure that the lowest tier does not slide when the ship rolls.
Containers carried on deck Typical bulk carrier stowage arrangement with b uttresses, using single/double Containers are usually stowed stacking cones and bridge fittings longitudinally in vertical stacks.
Containers within each stack are Containers carried below deck fastened together with twistlocks. The without cell guides bottom corners of each base container are locked to the deck, hatch cover or Containers are generally stowed in pedestal with a twistlock. When stacked the fore and aft direction, with the in multiple tiers, the containers are containers secured using locking usually lashed to the ship’s structure devices only or by a combination of by diagonal lashing rods. locking devices, buttresses, shores or lashings. The aim is to restrain the The lashing rods are usually applied containers at their corners. Twistlocks to the bottom corners of second or are very good at preventing corner thirdtier containers. On ships fitted separation. with lashing bridges, the lashing rods may be applied to the bottom corners When carrying containers in the hold of fourth or fifth-tier containers. of a bulk carrier or general cargo ship, base containers are secured with Lashings are applied so that each con- twistlocks or cones. Buttresses should tainer stack is secured independently. be fitted to provide lateral support. In theory, the loss of one stack should A platform, with sockets for cones or not affect its neighbours. twistlocks, may be fitted in the forward and aft holds. This forms the basis Transverse stowage, although possible, for block stowage of containers when is uncommon, mainly because cargo combined with cones, twistlocks and could move or fall out of the container bridge fittings. when the ship rolls, but also because principles of stowage / 41
transverse stowage requires rotation Containers carried at the sides of of the spreader bar of the shore gantry the ship are subject to wind loading. crane. Consequently, it is common for ‘wind lashings’ to be fitted. These may be In some cases, containers are carried vertical or diagonal. It may also be on deck in cell guides, in which case, necessary to fit wind lashings inboard the principles on page 33 apply. The if there are vacant stacks. same principles also apply to hatch- coverless container ships.
Typical arrangements for containers stowed on deck
Containers secured by twistlocks. Usually for two tiers only
Containers secured by twistlocks and lashing rods. Lashing rods to bottom of second tier. Wind lashings to bottom of third tier 42 / container securing / NNPC
Containers secured by twistlocks and lashing rods. Lashing rods to bottom of third tier
Typical stowage Typical stowage external lashings with external lashings parallel lashings without parallel lashings
Containers secured by twistlocks and lashing rods, ‘External lashing’ arrangement
As above but lashings originate from a lashing bridge. Lashing rods to bottom of fifth tier principles of stowage / 43
When stowing and securing 45-foot containers fitted with containers, the following additional corner posts at 40-foot points should be borne in spacing can be stowed on top of mind: 40-foot containers. Lashings can be applied in the normal way. It should be a deck stack of containers is only noted, however, that the additional as strong as the weakest component corner posts may not be suitable for in that stack. Premature failure of a carrying the required loads, either component can cause loss of an entire from the container itself or from those stack. During loading, containers stowed above. Lashings should not be should be inspected for damage and, if applied to the overhang. The container damaged, they should be rejected specification and the Cargo Securing Manual should be consulted twistlocks limit vertical and trans- verse movement. Diagonal crossed 40-foot containers may be stowed lashing rods, placed at the ends of a on top of 45-foot containers. However, container, can withstand large tensile this arrangement of stowage will loads present difficulties in fastening/ unfastening twistlocks, and it will not outside lashings are sometimes used. be possible to apply lashings to the These are lashings that lead away from 40-foot containers a container. However, although this arrangement provides a more rigid when carrying over-width contai- stow than a combination of crossed ners, for example 45-foot or 53-foot lashings and twistlocks, it is less containers with width 8’-6”, adaptor common platforms may be used. These must be certified by a class society or an containers exposed to wind loading appropriate recognised body. The need additional or stronger lashings. arrangement must be defined and When carried in block stowage, it is approved in the ship’s Cargo Securing the outer stacks that are exposed to Manual wind loading. However, when carried on a partially loaded deck, isolated twistlocks should always be locked, stacks and inboard containers can also even when the ship is at anchor, be exposed to wind, in which case, except during container loading and additional lashings need to be applied unloading. Lashing rods should be kept taut and, where possible, have even if containers of non-standard length, tension. Lashing rods should never that is, 45, 48 or 53 feet are carried, be loose nor should they be overtigh- the ship arrangement will need to be tened. Turnbuckle locking nuts should specially adapted be fully tightened 44 / container securing / NNPC
as a ship rolls, pitches and heaves carefully check twistlocks that in a seaway, tension, compression stevedores return to the ship as the and racking forces are transmitted locks might not originate from your through the container frames, lashings ship, that is, their strength and locking and twistlocks to the ship’s structure. direction could differ However, clearances between securing components and the elasticity of the discourage stevedores from treating container frame and lashing equipment lashing equipment roughly as this can produce a securing system that forms a induce weakness flexible structure. Thus, a deck stow of containers will move examine dovetail foundations, D rings and pad-eyes for damage. containers can be held by only Repair if damage is found twistlocks when two or three tiers are carried on deck, depending upon observe the loading of containers to container weights determine if stowage is in accordance with the stowage plan and that best arrangements with automatic and practice is always followed semi-automatic twistlocks are used to reduce time spent securing the stow observe the application of lashings and to eliminate the need for lashers to to make sure that they are correctly climb the stacks applied in accordance with the require- ments set out in the Cargo Securing Checks and tests during Manual discharge and loading
regularly examine lashing components, looking for wear and tear, damage or distortion. Check that left-hand and right-hand locking twistlocks are not being mixed in the same storage bin. Remove from the ship any lashing component found to be worn, damaged or distorted
make arrangements for some damaged or distorted lashing components to be sent for non- destructive testing. This will determine their strength and help to establish replacement criteria principles of stowage / 45
Transport of 40-foot containers
Checks and tests at sea re-check lashings after passing through bad weather 24 hours after sailing, examine, check and tighten turnbuckles. Check make sure that lashing equipment that lashings are applied in accordance that is not in use is correctly stored in with the Cargo Securing Manual and baskets or racks that twistlocks have been locked make an inventory of lashing examine lashings daily. Check that equipment and order spares before they have not become loose and they are needed tighten turnbuckles as necessary check that refrigerated boxes remain before the onset of bad weather, connected to the ship’s power supply examine lashings thoroughly and tigh- ten turnbuckles, being careful to keep an equal tension in individual lashing rods. If necessary, apply additional lashing rods to the outboard stacks and to stacks with 20-foot containers in 40-foot bays 46 / container securing / NNPC 11 ship’s behaviour
Container ships, due to the nature of their trade, are required to keep to very tight operating schedules. Maintaining the schedule is an important part of the liner trade. As a result, these ships have powerful engines, not only to provide the high speeds required, but also to enable speed to be maintained during bad weather.
The consequence is that, at times, strength of the tanktop, the cell guides container ships can be driven hard. and, on deck, the strength of the hatch When ships are driven hard in bad covers, lashing bridges, pedestals and weather, the loads on the lashings can the fixed fittings associated with the be severe. container stow.
There are many load components It is important to carry containers arising from a ship’s motion. These are within the loading conditions imposed discussed below. by the classification society. Container loads should never exceed the limits Ships’ structure set down in the ship’s loading manual.
The combined weight of a stack of Container strength and ship containers may amount to a total motion downward force on the tanktop, through each container corner casting, Although a ship has six degrees of of up to 100 tonnes. When four contai- motion, it is roll, pitch and heave ner corners are placed close together, which produce the most significant such as at the mid-hold position when contributions to the forces on a contai- carrying 20-foot containers, the total ner stow. Surge is important for road local load on the tanktop may be four and rail transportation and containers times this load. are designed with this in mind.
During classification, the strength The motion of a ship in irregular seas of the ship’s structure to support is itself irregular and is impossible to containers is verified and approved. accurately predict. Consequently, when This includes assessment of the calculating accelerations on a stack ship’s behaviour / 47
of containers, regular cyclic response The assessment of the effect of green is assumed in association with an seas on exposed container stacks is by assumed maximum amplitude. necessity empirical. The general princi- Empirical formulae for maximum ple is to require the container securing amplitude and period of response are arrangement in the forward quarter of defined in the Rules and Regulations the ship to be suitable for forces for the Classification of Ships by increased by 20%, except when the Lloyd’s Register. Rolling motion is ship has an effective breakwater or dominant in the calculation of forces, similar. but rolling must be considered in association with the other components Calculations of forces acting on a of the ship’s motion to establish the container consider various combina- largest likely combination of forces tions of the individual components of which the stow may experience. motion. Within each combination it is necessary to define the instantaneous For calculation purposes, the forces positions in the cycle of motion at acting on a container may be resolved which the calculations are made. into components acting both parallel to, and perpendicular to, the vertical Of course, in an actual seaway, all axis of the container stack. Gravity components of motion act simultane- acts vertically downwards and, ously to a greater or lesser extent. therefore, when the stack is inclined at maximum roll or pitch, there are force Lloyd’s Register Rules components of static weight acting allowable forces on an ISO both parallel to, and with, the vertical container (ISO 1496-1:1990) axis of the stack. The dynamic components of force are vectors. These The calculation of the forces in the are combined algebraically with the lashing arrangements is clearly a very static components. complex matter. This is further exacerbated by the de- Wind is assumed to act athwartships flections of the hull. For example: and to affect only the exposed stacks on the windward side of the ship. The the cross-deck structure may move magnitude of wind force, for a wind by as much as 50mm as the containers speed of 78 knots, is about 2 tonnes surge forward and aft on the side of a 20-foot container and about 4 tonnes on a 40-foot. The as the ship makes its way through a vertical component of wind on the top head or stern quartering sea, the hull of the uppermost inclined container is twists, distorting the hatch openings ignored. 48 / container securing / NNPC
calculation of forces
Parametric rolling wavelength of the predominant swell is comparable to the ship’s length The term parametric roll is used to describe the phenomenon of large, wave height is fairly large unstable rolling which can suddenly occur in head or stern quartering seas. ship’s roll-damping characteristic is Due to its violent nature and the very low large accelerations associated with the onset of parametric rolling, there is If resonance occurs between the wave widespread concern for the safety of encounter period and the natural, or container ships. Possible consequences twice natural, roll period of the ship, include loss of containers, machinery then parametric roll motion can be failure, structural damage and even experienced. capsize. Why are large container ships Parametric roll is a threshold pheno- vulnerable? menon. This means that a combination of environmental, operational and Fine hull forms with pronounced bow design parameters need to exist before flare and flat transom stern are most it is encountered. vulnerable to parametric roll. Such features contribute to the varia- These are: tion of the ship’s stability characteris- ship sailing with a small heading an- tics due to the constant change of the gle to the predominant wave direction underwater hull geometry as waves (head or stern quartering sea) travel past the ship. ship’s behaviour / 49
Although this phenomenon has been for resiliently mounted engines, studied in the past, it has only come problems with the connection of to prominence with the introduction services – and hence shutdown of the of the larger container ships. Until the main engine. 1990s, it was considered critical only for ships with marginal stability and The following points should be borne fine-lined warships. in mind:
Consequences of a parametric parametric roll is a relatively rare roll phenomenon occurring in head or following seas, which is characterised A parametric roll can have dire by rapidly developed, large, unstable consequences for container securing ship rolling and for operation of machinery. risk control options exist in both It is an extreme condition for contai- design and operation of container ner securing since it combines the ships that can effectively reduce effect of large roll and pitch amplitu- the likelihood of a parametric roll des. This scenario imposes significant occurring. Reducing the likelihood of loads on container securing systems. its occurrence is considered a more effective approach than mitigating the In theory, the container securing consequences system could be designed to withstand such extreme motions. The consequen- compliance with Lloyd’s Register’s ce would be a significant reduction in current requirements for container the number of containers that could be securing systems can reduce the risk of carried on deck. So, essentially, there is container losses a balance between increased container security and the limitations imposed masters should be aware that when by securing requirements. conditions for parametric rolling exist, ie. head/stern seas with wave length The extreme roll angles reached during similar to the ship’s length, the action a parametric roll usually exceed those of putting the ship’s head to the sea adopted during machinery design. and reducing speed could make rolling Indeed, it would be very difficult to worse. Other action to ease the ship’s bench test a large marine diesel engine motion will be necessary, depending at 40 degree angles. Possible conse- upon the prevailing weather quences on machinery operation of the ship heeling to these very large angles the North Pacific in winter is include loss of cooling water suction, especially prone to these conditions exposure of lubricating oil sumps and, 50 / container securing / NNPC
Outboard container damaged by heavy sea consequences of failure / 51 12 consequences of failure
case study The consequence of failure is almost always loss or damage of containers. The club has been involved in every type of incident following container loss, from widespread pollution after a floating container hit a ship’s hull and pierced a fuel tank, to wreck removal when sunken containers contained toxic chemicals, to a seaman hit by cargo falling from an open container. The study which follows graphically illustrates how simple faults, on a well run ship, can give rise to large container losses and the incidents described above. 52 / container securing / NNPC
Collapsed container – crush damage
It was February and the Panamax third tier containers. The ship’s GM container ship had loaded in Northern was 2.0m. hemisphere ports for China. She had seven holds and could carry over 3,000 The schedule required sailing south containers, although less had been along the western seaboard of the Uni- loaded on this occasion. Loading was ted States before crossing the Pacific homogeneous, without isolated stacks, to Japan and China. The ship was on a but heights of containers differed. southerly course when she encountered Containers were loaded on deck, five strong head winds with heavy head high in some bays and three high in seas and swell. She was pitching and others. Lashings consisted of base rolling heavily with occasional rolls to (manual) twistlocks fitted into dovetail very large angles when a loud crash foundations with semi-automatic was heard. It was suspected that twistlocks used between containers. containers had been lost or had Parallel crosslashings were applied shifted. Next morning the extent of using short and long lashing rods with damage could be seen; the entire stack turnbuckles. These connected to the forward of the bridge had collapsed. top corner of first tier containers and Many containers remained on board to the bottom corner of second tier but some had fallen overboard. containers. Wind lashings were applied Investigations revealed that a number on the outboard stacks with long rods of classic mistakes had contributed to connected to the bottom corner of the loss. consequences of failure / 53
Course and speed During the conditions of very severe rolling, containers stowed on deck can The ship was proceeding on a southerly be subjected to massive separation course into head seas and was pitching forces, forces that are likely to exceed and rolling heavily. Rolling in head the combined strength of the securing seas may be associated with the system. Parametric rolling may be phenomenon known as ‘parametric prevented by alteration of course or rolling’ which occurs because the change of speed. ship’s waterplane area changes as waves pass along the ship’s length. Stowage and securing Maximum rolling can occur when a wave’s length is comparable to the The bottom container in each stack ship’s length. At the instant when the was secured by twistlocks fitted to ship’s midship is supported by a wave dovetail sockets which slide into crest, with the bow and stern in a dovetail foundations. Dovetail founda- wave trough, there is an instantaneous tions, for a variety of reasons, have a loss of waterplane, sudden and tendency to wear which can result in massive loss of righting force and the movement of the securing twistlock. ship may roll to very large angles. In extreme circumstances the base As the wave passes along the ship’s twistlock can be pulled out of the length the situation is reversed, strong dovetail foundation leaving only the righting forces are exerted and the ship lashing rods to hold containers in rights herself but only to roll again as place, something which they are not the next wave passes. Effectively, the designed to do. This had happened and ship performs simple harmonic motion as a consequence turnbuckles had but with violent rolling. pulled apart and lashing rods had broken.
One end of the lashing rod was connected to a D ring and D rings were welded to the lashing bridge for this purpose. Some of the D rings had been pulled apart and it was found that D ring securing collars had been poorly welded and were weak. Quality of welding is a matter for new build superintendents, not the ship’s crew but during routine maintenance, chipping and painting, welds which Lashing failure causing container loss connect securing points to the ship should be examined for corrosion, 54 / container securing / NNPC
The ship had been loaded in accor- dance with the limits imposed by class and nothing improper was found with container distribution or stack weights. However, mathematical simulation of the forces imposed on the containers during violent rolling indicated that racking and compression forces on the containers exceeded the design strength of lashings by 1.5 and 2.5 times respectively. This would have resulted in very large separation forces on the stacked containers. Prior to the failed twistlock incident the crew had checked that turnbuckles were evenly tightened but damage or defect with any observed they had not applied additional wind deficiency being reported to the lashings. Any additional lashings master. On this ship D ring collar welds applied in exposed locations before had very poor penetration and the the onset of severe roll and pitch securing point was weak. conditions should improve combined lashing strength, provided the lashings This is not something a ship’s crew are applied to the bottoms or tops of can correct but an observant seaman containers which are only secured by who spots a defect and reports it can twistlocks. be instrumental in preventing a major loss. Base foundations need regular With the benefit of hindsight it is seen examination and test, something how simple errors can cause container which should form part of the ship’s loss. The weather conditions experien- planned maintenance procedure. ced were not extreme but the effects of parametric rolling, worn base Not all base twistlocks had failed, foundations and weak ‘D’ ring collars some were found unlocked and it was all contributed to the catastrophic suspected that the ship had been using loss of containers. It is rarely a single left-hand and right-hand locks in the failure that results in a loss but a same stow. Using left-hand and right- sequence of events. For this reason it hand locks in the same stow makes is essential to follow best practice and it very difficult to detect whether a the principles set out in this guide. twistlock is actually locked or open. Ship’s crew should be checking for incorrectly handed locks and removing them. foto wim te brake A MASTER’S GUIDE TO:
NNPC Rijksstraatweg 361 9752 CH Haren (Gr.) www.nnpc.nl [email protected]
Authors Eric Murdoch, Chief Surveyor Standard P&I Club David Tozer, Business Manager Container Ships Lloyd’s Register
Photo cover Wim te Brake, Amsterdam
Design In Ontwerp, Assen