Answering the question will be difficult because cargo is only a name for different kinds of products which will be transported from one point of the earth to another. This can be done by car, aircraft, truck, or ship. The most useful kind of transportation and also the most efficient kind of transportation is the ship.
A ship can carry, compared to a truck or railway, much more different products and also more masses. These goods will be transported generally for commercial gain.
In general we know:
There are also some special cargoes which are partly belonging to the kinds of cargoes mentioned above, like dangerous goods which can be either dry cargo, refrigerated cargo or liquid cargo.
Each of the above mentioned kind of cargoes has special parameters to be known. Without knowing these parameters, a transportation of cargo is not possible. The different cargoes will be discussed in chapter 2, but for all cargoes to be loaded, general guidelines can be worked out. These guidelines should be followed prior loading, during loading, prior and during discharging and also during the voyage.
The planning for loading and discharging of cargo is a compact unit. First of all we have to calculate the cargo, which means how much cargo can be loaded. The planning for the cargo operation is based on the cargo to be loaded. The quantity of the cargo to be loaded will be given by the charterer. The Master and/or Cargo Officer (normally the Chief Officer) have to check and clarify if the ship can load the said amount of cargo.
The next step – and for most of the vessels the first step – is where is the cargo bound for – what is the discharging port(s). For the calculation of the planned voyage the master not only needs to know how much cargo can be loaded, further he also must know:
There are for sure many more aspects the ship command must take into account, but these are the most important ones.
The distance between the POL and POD1 will be needed to calculate the required amount of fuel oil which will be consumed during the voyage. The HFO and MDO consumption has a direct influence on the load line regulation and the stability/trim of the vessel and as well for the distribution of the cargo. The consumption of fuel oil is one of the most important parameters to know prior loading especially when loading cargo in bulk.
The simple formula for the calculation of the consumption is:
Total consumption = Total time used for the voyage (in days) * HFO (MDO) consumption per day
There is still one factor missing in the consumption calculation. The factor missing is the safety margin for weather influences (bad weather on the voyage which causes the ship command to deviate from the origin voyage plan). This will result in more consumption of fuel oil which must be taken into account. The safety margin can be obtained by 15% to 25% more bunkers to be on board.
For example:
The daily consumption of the vessel = 35mt. The voyage takes 10 days.
Consumption = days * consumption/day
= 10days *35mt = 350mt/voyage
SafetyMargin = 25%
25% of 350mt = 87,5mt
Total Bunkers on Board = 350mt + 87,5mt = 437,5mt
The conclusion will be: Total consumption + Safety Margin = Required Bunkers/Voyage
The safety margin will differ due to the different bunker capacities of the ships and the daily consumption rate.
Another parameter for the pre-calculation of the cargo is the deadweight and displacement of the vessel. The detailed calculation is part of “Stability &Trim”. But the draft of the vessel is important for the planning of the voyage because the ship command must comply with the load line zones the vessel will trade in. Furthermore, the required maximum drafts in the POL and POD – given in the draft limitations – are part of the displacement calculation.
After knowing how much cargo must be loaded (charterer’s figures) the ship command must calculate if the cargo can be loaded on board of the vessel.
Each cargo requires a different kind of stowage (see also Chapter 2 – “The different types of cargo”). For this reason the ship command must check prior loading if all necessary stowage material and lash material is available on board to guarantee a good stowage and loading/discharging procedure. All checks should and must be done prior loading. The ship command has to declare that the vessel is ready for loading (N.O.R)2.
For the stowage of the cargo, the Stowage Factor (S.F.) of the cargo must be known. The stowage factor is a mathematical figure which expresses how much space will be occupied by the cargo if the said cargo will have certain measurements (H*L*W)3. This will be expressed in the S.F. It is the Volume occupied by the unit weight of cargo expressed in cubic meter or cubic feet.
The stowage factor will normally be given by the charterer, but it can also be calculated.
Formula for S.F.:
For example:
The total cubic meter of the hold = 3000m3. The vessel has actually loaded 650mt.
For most of the cargoes to be loaded, the stowage factor is already known or given by the charterer in advance. It is necessary for the ship command to have the S.F. in advance to prepare a preloading plan. The measurement of the hatches and the theoretically cargo to be loaded can be found in the vessel’s capacity plan.
The stowage of the cargo differs also with the cargo to be loaded and how exact the stevedores will work as well as how exact loading and stowage of the cargo will be supervised by the Officer of the Watch.
For a tanker, for example, the maximum filling of the tanks depends on the property of the cargo4. In general, the upper limit = 98% of the tank volume.
Starting from the vessel’s displacement on departure, the net in taken cargo can be calculated by subtracting the vessel’s light ship. Therefore: Departure displacement – light ship weight = gross displacement. If subtracting all other weights (fuel oil, provision, ballast water, crew effects, paints etc.), except for the cargo weight, from the gross displacement, you will get the net displacement of the ship.
Another important factor in respect to the stowage of the cargo is the broken stowage. The broken stowage can be also calculated.
Broken stowage is defined as the amount of space on a ship that is lost during stowage, measured in percentage of total bale space5. The percentage of space lost varies depending on the type of cargo, container shapes, and the bays used.
Therefore:
where: V = Total volume of the cargo Hold
v = Volume occupied by the cargo loaded
The broken stowage is then the space between the packages which remains unfilled due to bad stowage expressed in percentage.
Example:
The total volume of a cargo hold = 3000m3. After loading, the ship command calculates the occupied space with 2500m3.
In this example, the broken stowage for this hatch will be 16,7%.
The broken stowage is a result of packing material which was used, or the ship’s design in the holds (remember: not all areas can be used for the stowage of cargo but are part of the area calculation in the hatches). Often times the case is: Just a result of bad stowage done by the stevedores.
Is the loss of stowage higher than agreed in the charter party, the master has to protest against the loss of stowage using the letter of protest to protect the vessel and the ship owner against any claim done by the charterer.
First: The distribution of the cargo is normally part of the ship command. It depends on the kind of cargo to be loaded and the type of vessel (Compare Bulk Carrier with a container ship or General Cargo vessel). On a container ship, the stowage plan is already prepared by the cargo planner ashore and therefore also the distribution of the cargo. Here the ship command only has to check that the distribution (weight distribution) is in accordance to the limitation of the ship’s longitudinal strength and stability and trim criteria.
Illustration 1: Normal Longitudinal Strength Curve of Feeder Container Vessel
The cargo distribution has to be done in accordance to the longitudinal strength condition and limits of the vessel. In order to obtain this requirement, the vessel will be loaded and discharged in sequences which have to be strictly followed. If the shear and bending stresses are above the limits, the cargo must be distributed so that these limits will not be overdue. This can be achieved by ballasting or de-ballasting, but sometimes this is also not possible anymore – then the distribution must be changed.
Second: The port criteria have to be observed and checked.
These are influences on the cargo distribution.
Third: Kind of cargo to be loaded: For example, Iron Ore: Iron Ore cannot be loaded in all hatches. The loading procedure, certified by the classification society, must be strictly followed.
Logs and sawn timber, for example, have to be distributed in accordance to the relation hatch to deck, so as not to suffer any stability problems.
Fourth: Trim and draft – The cargo has to be distributed so that the trim and draft will not affect the maneuverability of the vessel or the load line convention.
Whenever trim, stability, or longitudinal strength is not in accordance with the given figures in the stability booklet (approved by the classification society), the distribution of the cargo must be changed in order to fulfill the requirements given by the classification society. The changes must be discussed with the charterer or his representative.
Fifth: The distribution should also be in accordance with the lashing arrangements (for example: Log and timber cargo in accordance with the International Timber Code, or Bulk Cargo with the BLU-Code).
Sixth: Distribution should be done in accordance with other cargoes to be loaded (separation of cargo. See Dangerous goods – IMDG Code). Other cargoes are reacting to the odor of the cargo stowed nearby.
Seventh: Distribution in accordance with loading and discharging facilities (Grain, Coal in Bulk, Heavy Lift, Reefer cargo).
Eight: Distribution in accordance with other loading and discharging ports – Port sequence must be observed and taken into account.
The above presented eight rules for stowage and distribution are showing us that the start of a successful transportation of cargo is depending on the preplanning that is done.
1 POL = Port of loading and POD = Port of discharging
2 NOR = Notice of Readiness. Will normally be tendered prior loading by the master of the vessel to the charterer or agent to state that the vessel is ready to take the said amount of cargo.
3 Height x Length x Width of the cargo to be loaded
4 Liquid cargoes, like oil products, are gassing which cost an increase of their volume
5 The cargo capacity of a vessel below deck, measured in cubic meters or cubic feet.
Over the past 30 years, the container has been the most common cargo transportation unit on board of merchant vessels. Nearly all kinds of cargo can be transported with and in a container, from Reefer Goods to Heavy Lift, Bulk cargo, Liquid cargo and General cargo. To transport these kinds of cargoes, different types of containers have to be designed. In general, a container is a small hold and has to be treated as if it would be a cargo hold.
We know different types of containers:
The 48’& 49’ and especially the 53’ containers are often times used for transportation to the USA. Especially for these types of containers the ship must be designed for. The mate on board must have knowledge about the different types of containers, where they can be stowed, and the different parts of the containers. The last-named is very important for damage reports.
The container is a weak box loaded with heavy cargo inside and above. The mass of the cargo is accelerated by the six types of movement of a ship in response to sea conditions and by additional forces from wind and green seas. To handle these forces and to secure the valuable cargo, containers need to be further stabilized and secured by lashing equipment.
Illustration 2: Six Movements of a Ship
The stresses acting on the containers are in vertical, horizontal, and transversal direction.
Illustration 3: The Different Construction Parts of a Container
Illustration 4: Bottom Construction
The above presented parts are the same for all containers. Some containers have additional parts like integrated reefer units etc.
If the container is loaded to its maximum capacity, the weight of the cargo must be distributed as evenly as possible over the floor area. The load-carrying components of the container floor structure are the bottom side rails which absorb the load of a cargo via the container floor. For safe transport it is important for as many of the bottom rails as possible to be loaded. Point loads are to be avoided, since they can damage the container floor. Point loads always occur when relatively high weights are concentrated on a small bearing area.
If planning the cargo stow inside the container, also the maximum line load is of importance. For 20’ and 40’ container it states a maximum line load of 4.5 metric tons/m for a 20' container and 3.0 metric tons/m for a 40' container.
Example 1: A cargo weighing 14 t extends over a length of 5,3m. This gives a line load of
The result shows that this cargo could be transported in either a 20' or a 40' container as 2,64mt<4,5mt for a 20’ container and 2,64<3,0mt for a 40’ container. The limits of the line load will be not exceeded.
Example 2: A cargo weighing 18t extends over a length of 5,3m. This gives a line load of
This cargo could only be transported in a 20' container. In a 40' container the maximum line load would be exceeded and transport would therefore be disallowed.
However, the cargo can be also packed in a 40' container. Therefore, the bearing area must be enlarged to ensure safe transport. This may be achieved, for example, by laying dunnage or a "sled" under the cargo. Where dunnage is used, it must be ensured that the lower wooden planks lie lengthwise and are thus supported by several container bottom cross members. If using sleds, the skids of a "sled" must also lie in the lengthwise direction of the container.
The cargo loaded in a container will be mostly on pallets. This allows a fast loading and discharging of the cargo inside the container. Reefer cargo will be also single stowed, i.e. package by package.
Before the container will be loaded, the container has to be cleaned from inside, all old residues have to be out, the container must be free of any odor and there has to be an inspection after the cleaning by the company who is responsible for the stowage of the container. A lot of container damage claims are based on the fact that the cargo was affected by bad odor resulting from previous cargo. If the container is free of any odor, the container can be loaded. It is now up to the shipper to distribute the cargo in the container. Here it is usually practice that a stowage plan is prepared, as well as a lashing plan how the cargo will be secured inside the container. Sensitive cargo should be further protected against sweat water and humidity which can destroy the cargo. If, for example, the humidity of loaded coffee is exceeding 13%, a fully ventilated container must be used.
Illustration 5: Fully Ventilated Container
It should be assured that the inspection of the container and the cargo to be shipped in the container must be carried out by the shipper or the company who are packing the container on behalf of the shipper. An inspection certificate should be issued to state that the container was dry.
This inspection cannot be rechecked by the ship command; when the container will be loaded, the container is already sealed and cannot be opened anymore by the officers. Only if there are differences between the loading papers and the actual cargo inside the container, the master can make a protest and the shipper must now proof that all the information is in accordance to the cargo loaded. If not, the container should not be accepted by the master.
Another problem for the ship command is the securing of the cargo inside of the container. Cargo stowed in containers must be secured on all sides to prevent shifting, in particular towards the door. Spaces between packages and/or container walls must be filled. Secure the cargo by using the lashing points provided on the top and bottom side rails and on the corner posts. Containers should be packed and the cargo secured in accordance with guidelines for packing cargoes other than bulk cargo in or on cargo transport units (CTUs) for carriage by any means of transport at sea and ashore.
The CTU packing guidelines published by the International Maritime Organization (IMO) and International Labor Organization (ILO) from 02-05-1997 supersede any previous applicable container packing guidelines.
The container is a standardized cargo, meaning the measurements for the different container types are already fixed. These are standard measurements. The normal standard 20’ and 40’Container measures are:
20’ Container: 20’ x 8’ x 8’6’’ = 6,096m x 2,438m x 2,591m (LxWxH)
40’ Container: 40’ x 8’ x 8’6’’ = 12,192m x 2,438m x 2,591m (LxWxH)
The container will be identified by its identification Number according to the ISO6346.
Illustration 6: Identification acc. ISO 6346
Illustration 7: Size and Type Code – 6346
Illustration 8: Volumes and Weights Marking
The container will be stowed according to an international system of numbering the location of the container. To locate a container on board and also to make a correct stowage plan (Bay Plan), the system is divided in bays, rows and tiers – on deck and in the hatches. This numbering is an international standard.
Bays: Each container loaded is split into compartments which will be termed as bay. The bays are depending on the size of the vessel. For example: It will proceed from 01 to 60. Bay 01 is the first bay forward of the ship and Bay 60 is the last one, near the stern of the ship. Odd numbered bays are 1,3,5,7 etc. and are for 20’ container stows, and even numbered bays, 2,4,6,8 etc., are for 40’ container stows. Between two 20’ bays there is a 40’ bay. There are exemptions because on some ships where no 40’ container can be stowed we will have special 20’ container bays. The same holds for 40’ container bays.
Rows: The position where the container is placed across the width of the vessel. The odd numbers are on the right side and the even numbers are on the left side.
Illustration 9: Bays, Rows, and Tiers on Deck6
If the ship can load 10 containers from side to side, the number of rows is an even number, then no zero row will be used. If the ship can, for example, load 11 container from side to side, then a center row, the zero row, will be used. Illustration No.9 is presenting an amount of odd numbered rows. Here the zero row will be used.
Illustration 10: Rows Including Center Row7
Tiers: The tiers are marking the level where the container is loaded. The tier numbers on deck are always starting with 8, followed by even numbers, and in the hatch they start with a 0, followed by even numbers. Example Deck: 80,82,84,86,88,90,92 etc. In the hatch: 02,04,06,08,10,12, etc.
see Illustration No.11 for a better understanding:
Illustration 11: Bayplan with Bay, Rows and Tiers8
The distribution must be exactly in accordance to the bay plan (Illustration No.11).
In the Illustration above, there is one reefer container loaded for Bangkok (BGK (R)). The container is located as follows: 07/02/80. = Bay 07/Row o2/Tier 80. Actually, we can identify more because the container is loaded forward on the ship, portside in the first layer on deck, and it is a 20’ Container because the bays are numbered from forward to the aft, as we said starting with 01 etc. Bay 07 is a 20’ Bay.
6 Peter Grunau – Own drawing
7 Peter Grunau – Own drawing
The lashing material and also lashing arrangement is in accordance to the Cargo Securing Manual, CSM, which each vessel must have. The CSM is approved by the Classification Society and has to be strictly followed. The required lashing material and also the required lashing arrangement for this type of vessel is listed and presented in Illustrations. Besides the material to be used, the handling instruction for each bay, row and tier is included, as well as the maximum stacking weight per tier for each bay.
The lashing material to be used must be in accordance to the stress acting on the container and this is different for a full container vessel of 900 TEU or a full container of 12000 TEU. Also, for ships that are certified to carry containers on deck and in the hatches but are actually no container ships, the stress is acting on different locations and is never the same.
Before we are now listing and discussing the lashing materials and their use, at first we have to understand what kind of stress is acting on the container.
We have already seen that the container normally always has the same construction parts. The construction part which is actually the strongest one and can withdraw also the highest stress is the corner post. A container is designed in a way that 9 containers can be stapled on top of each other. All other parts are much weaker. Therefore, also the maximum stress acting will be mostly found on the corner post and the corner casting. Therefore, these parts of the container are reinforced and much stronger than the other ones.
Illustration 12: Allowable Forces on an ISO Container9
Looking at the Illustration above, we will see that the vertical compression on the corner casting is the highest of all stress which is allowed as well as the transverse compressive reaction force on the upper and lower corner casting. The other form of stress is the racking stress which is for the upper and lower part of the container the same = half of the force of the lashing rod. That means also that the twistlock must overcome these stresses as well. The Illustration No.12 presents us the results of different influences on the container if the distribution in the stack will change, without exceeding the stack weight of each stack.
Forces acting in a container tier. Distribution of weight = 30mt in 4th, 3rd and 2nd tier. Changing of the physical parameter (T, F, v, P.E) if the distribution of the 30mt will change from 2nd tier to 4th tier. In this example, the stability changes are not included. But if the weight will be loaded in the last tier, the center of Gravity, CG, will also rise upwards, causing a reduction in the stability. The momentum of inertia of the container tends the container to lack behind the rolling, caused by waves. If the ship rolls back, the container will still move to the outer side. This will increase the force acting on the lashings and the construction of the container.
Illustration 13: Forces Which Influence the Container and Lashing10
The forces which are now acting on the container and which are also varying will at the same time also have an influence on the lashing arrangement. This is already foreseen in the Cargo Securing Manual and the lashing materials including their Breaking stresses are in accordance with the CSM.
The lashing material should always have the ability to come back to its original length (see also Hooke’s Law). If the lashing material is once deformed, it will lose the holding power, vertical and transverse holding power, and is therefore useless for us.
| Tier | Mass [kg] | HeightTier [m] [m] | Acceleration [m/s2] | Velocity [m/s] | Period [s] | Force [kN] | Pot. Energy [kJ] | Kin.Energy [kJ] |
| 1 | 2500,00 | 2,45 | 9,81 | 127,53 | 13 | 24,53 | 60,08625 | 20329,88 |
| 2 | 8000,00 | 4,9 | 9,81 | 127,53 | 13 | 78,48 | 384,55 | 65055,60 |
| 3 | 4000,00 | 7.35 | 9,81 | 127,53 | 13 | 39,24 | 288.41 | 32527,80 |
| 4 | 15000,00 | 9,8 | 9,81 | 127,53 | 13 | 147,15 | 1442,07 | 121979,26 |
| 5 | 15000,00 | 12,25 | 9,81 | 127,53 | 13 | 147,15 | 1802,59 | 121979,26 |
| 6 | 15000,00 | 14,7 | 9,81 | 127,53 | 13 | 147,15 | 2163,11 | 121979,26 |
| 7 | 20000,00 | 17,15 | 9,81 | 127,53 | 13 | 196,20 | 3364,83 | 162639,01 |
| 8 | 15000,00 | 19,6 | 9,81 | 127,53 | 13 | 147,15 | 2884,14 | 121979,26 |
| 9 | 15000,00 | 22,05 | 9,81 | 127,53 | 13 | 147,15 | 3244,66 | 121979,26 |
| Total mass | 109500,00 | Total Force | 1074,20 | |||||
Illustration 14: Force Acting on a Container in Different Tiers
Checking the kinetic energy in accordance with the weight distribution in the stack, we can see that the 20mt in the 6th tier has more kinetic energy at a constant velocity and acceleration than the 15mt container in the last tier. But in general, the kinetic energy is increasing with an increase of height and mass. If the Force acting on the container and the kinetic energy is increasing, the forces on the lashing material are also increasing.
| Tier | Mass | HeightTier | Acceleration | Velocity | Period | Force | Pot.Energy | Kin.Energy |
| [kg] | [m] | [m/s2] | [m/s] | [S] | [kN] | [kJ] | [kJ] | |
| 1 | 20000,00 | 2,45 | 9,81 | 156,96 | 16 | 196,20 | 480,69 | 246364,42 |
| 2 | 15000,00 | 4,9 | 9,81 | 156,96 | 16 | 147,15 | 721,04 | 184773,31 |
| 3 | 15000,00 | 7,35 | 9,81 | 156,96 | 16 | 147,15 | 1081,55 | 184773,31 |
| 4 | 15000,00 | 9,8 | 9,81 | 156,96 | 1–5 | 147,15 | 1442,07 | 184773,31 |
| 5 | 8000,00 | 12.25 | 9,81 | 156,96 | 16 | 78,48 | 961,38 | 98545,77 |
| 6 | 4000,00 | 14,7 | 9,81 | 156,96 | 16 | 39,24 | 576,83 | 49272,88 |
| 7 | 2500,00 | 17,15 | 9,81 | 156,96 | 1–5 | 24,53 | 420,60 | 30795,55 |
| 8 | 19,6 | 9,81 | 156,96 | 16 | 0,00 | 0,00 | 0,00 | |
| 9 | 22,05 | 9,81 | 156,96 | 16 | 0,00 | 0,00 | 0,00 | |
| Total mass | 79500,00 | Total Force | 779,90 |
Illustration 15: Homogenous Distribution in the Stack
Illustration No. 1511 is presenting a correct stowage and weight distribution in the stack resulting in a decrease of the force and the kinetic energy in the last tiers of the stack. The forces acting on the lashing will therefore also decrease.
Illustration 16: Force and P.E/K.E with Wrong Distribution in the Stack
Illustration 17: Force and P.E/K.E with Correct Distribution in the Stack12
We can see that there are nearly no forces acting on the container and, therefore, also not on the lashing arrangement in the last tiers, and that this distribution will keep a sufficient vertical and transversal holding power of the lashing system, compared to Illustration No.14 where we will face just the opposite.
It is important to calculate, nowadays done by computer, the dynamic loads acting on container and lashing material and the frames.
The IMO SOLAS A – Resolution 489(XII) requires vessels to carry onboard a Cargo Securing Manual drawn up to a standard contained in MSC/Circular 385 – 1996. This was extended to new container ships and to existing vessels in 1998. The IMO Guide lines require a Cargo Securing Manual in the form of MSC7Circular 745 superseded the MSC/Circular 385.
The SOLAS Chapter VI: Regulation 5 – Stowage and Securing states that the cargo and cargo units on deck or under deck should be loaded, stowed and secured to prevent, as far as it is possible, damages or hazards to the ship, the crew and the cargo throughout the voyage. Cargo and cargo container should be loaded, stowed and secured in accordance with the Cargo Securing Manual.
On container vessels, there are fixed and loose container lashing materials. Fixed lashing materials are the dovetail foundation, Cell-guides in the hatches, lashing rings (D-rings).
Loose container lashing materials are:
There are handling and safety instructions for the loose lashing materials which must be known and observed.
Securing Manual
Gap13 between the 20’ containers
for easy operation and controlling of the locking position. Never mix left hand and
right hand conventional twistlock
Pressure device(s) have to be correctly fitted (between the container corners)
be observed (Emergency Tool)
must be set with a minimum clearance to the longitudinal bulkhead. The reason
for setting this elements (will be used often times on reefer ships in the hatches)
is to reduce the movement within the container block
the yellow cone upside
vessel is in port at the berth.
As already mentioned, the lashing material must be in accordance to the CSM. On modern vessels, lash bridges are fitted. Lash bridges are steel constructions running athwart ships between the 40’ container bays. The 20’ containers can only take advantage of the lashing bridge at one end. If two 20’ containers will be stowed, only the forward part of the first one and the aft part of the second 20’ container can be lashed down to the lash bridge. The other two sides must be secured with twistlocks only. Therefore, the weight of each 20’ container is limited by the maximum capacity of the lashing/lashing system at the side where the lashing will be not connected to the lashing bridge. The advantage is that it allows the second and third tier container to be secured to the lash bridges, using lashing rods and turnbuckles. Another very important advantage of the lashing bridge is that it allows the anchoring points of each stack to be moved higher up the stack. The result is that the tipping moments which act on the stack when the ship is rolling will be reduced. Therefore, the lashing becomes more effective.
For the lashing of the container the most common materials are the semi-automatic twistlocks and the lashing rods/turnbuckles on deck and the cell guides in the hatches. In the hatches, there is normally, on full container ships, no securing of the container by means of lashing rods necessary as they will be guided and fixed by the cell guides.
The semi-automatic twistlocks have a big advantage compared to the conventional manual twistlocks. The twistlock will be placed already at the dockside, meaning that nobody must climb up the container stable to set twistlocks. Second of all, the loading and discharging is much faster because the unlocking of the twistlocks will be done via an unlocking tool which will be operated from the lash bridges.
Illustration 18: Lashings and Lash Bridge14
All containers stowed on board must meet the container standards. The securing system is based on the ISO container standard, if not otherwise indicated. All loose securing elements have to be applied as shown in the container securing plan. The plan must provide following necessary overview:
All securing devices must be certified by the Classification Society the ship is belonging to.15
Depending on the lashing arrangement and the position of the container (loaded on deck or in the hatch), there are different forces acting on the container and also on the securing device. During the calculation of the securing system, also the strength capacity of the containers which have to be secured should be considered, as there are:
The lashing can be generally seen as a reinforcement of the container frames. The container lashing has to be used so that the acting racking forces in the stack will not exceed 150kN. The weight distribution in the stack is very important and does not have to be exceeded. The weight distribution stated in the securing manual represents already the optimum distribution under the given circumstances.
As a general guide line of stowing and distributing of the container we can say:
First the extra heavy weight container – then the heavy weight container – medium weight container – light weight container and in the last two tiers or the last tier only empty containers.
a. Alteration of Weight Concentration in the Stack
An alteration of the weight downwards is possible, an upwards alteration of weight concentration is not possible. If loading a heavy weight container in the last tier, a continuous upgrading of the weight in each tier will be the consequence and will result in a tilting of the stack, an overstress of the foundations, twistlocks and lashings. Especially in the outer stacks the stack weight is less than elsewhere. Exceeding the stack weight will have severe consequences.
In general: an exceeding of the stack weight is not allowed.
b. Maximum Quantity of Tiers
The maximum quantity of the tiers should not be exceeded. If this will happen, the force acting on the securing system will increase and also the sight line could be interrupted.
c. Weight Distribution
The weight distribution in the container securing manual is based on 8’6’’ containers. For this reason it is not easily possible to stow a high cube container or any other heavy weighted container on top if this is not in accordance to the cargo securing manual. If I change the weight distribution in the stack – upwards change, the C.G will move upwards causing a decrease of the GM. Further, the securing system of the container will be overstressed, the forces are increasing. Avoid stowing loaded containers in the last tier(s).
d. Specific Features to be Considered
Each container can be considered as an outer stack container. The container should be lashed accordingly and, if necessary, the weight should be reduced in the stack. In case different stack heights are present (left side 6 high and right side 3 high), these containers have to be considered as outer stack container as well and have to be secured accordingly.
a. The Maximum Stack Weight is Exceeded.
The maximum stack weight should never be exceeded because of:
b. The Given Weight Distribution in the Stack is Exceeded
c. Not Locking of Container Twistlocks
d. Lashing not Foreseen With the Container Securing Manual
e. The Pretension in the Lashing is Exceeding 5 kN16
Extreme cases should always be avoided not to damage or lose the container.
The securing arrangement of the container should also be discussed with the stevedores because it might be necessary to set additional lashing for expected bad weather conditions during the voyage (expected tropical revolving storms etc.). Always be reminded: On board, the ship master is responsible for the cargoes loaded and their maximum security. Additional assistance can be also asked from the company’s supervisor for this ship.
If ships are in navigation, they encounter three main movements: pitching, rolling and heaving. These movements are also acting in form of acceleration on the container and container lashing system. Out of these movements, the separation force –tipping force, is also acting on the container and its lashing system.
a. Twistlocks are Broken:
The ship is rolling heavily resulting in an increase of the separation force. This can cause that the twistlocks will be pulled out of the corner casting, that the twistlocks break or that the corner casting is separated from the container body.
b. Damages due to Racking Force: