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Why it is important to check the stacking weights of a Containership stowage plan

Container stacks are containers which are stacked vertically and secured horizontally by stackers, lashing etc. Prior loading cargo, stacking weights of containers must be checked against the allowable stack weights on board the vessel both on deck and under deck. Neglecting above may cause serious damage to ships structure, hull and eventually overall stabilty of ship may get affected. Maximum allowable stack weights of Tank tops, Hatch covers and Decks shall not be exceeded at any time.

Container stack load – Hatch covers for Panamax ships have stack weights up to 90 tonnes/20ft units and 120 tonnes/40ft units. Post-Panamax vessel could have 100 tonnes/20ft and 140 tonnes/40ft units.

It is essential to avoid loading heavy containers over light, or at the top of a stack in a deck stow, unless specifically permitted in the Cargo Securing Manual. This is because the securing system would normally have been designed on the assumption that light containers are stowed on top. Stowage 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.

If any stacks are found to be exceeding the allowable stack weights, Terminal planner / Central planner is to be informed and cargo stow plan appropriately modified. The most common mistake made when stowing and lashing containers is to load heavy containers over light or to load so that the maximum permissible stack weights are exceeded. Heavy on light can only be accepted when specifically permitted in the Cargo Securing Manual.

In case such anomaly is noticed after containers have been loaded, the master shall notify all concerned parties and have the condition corrected at the earliest prior departure.

Container stowage in holds

The standard 40ft containers (FEU) are stowed in cell guides without any lashing devices. If there is also a certain number of 20ft units (TEU) available at all time, the creation of a hold with 20ft guides may be considered. In most cases, 40ft cell guides are installed exclusively and TEUs are stowed in the 40ft bays. This, however, needs securing job. There are basically 3 systems to stow TEUs into 40ft cell guides:
  1. Side support stowage system. The containers are connected with double stacking cones in a transverse direction. At the longitudinal bulkhead, you have either a fixable installed guide rail or foundations for buttresses that take up the load. This is the most conventional system. The containers can be loaded/removed only tier wise.



  2. Stowage with anti-rack spacers. The containers are connected longitudinally with so called “anti racking spacers”, thus creating out of two 20ft containers one 40ft-unit. This system avoids side supporting, that means a 20ft stack can neighbour a 40ft stack and there are no foundations or rails in the longitudinal bulkhead. The disadvantage is that the containers have to be loaded/ removed also tier wise.

  3. Mixed stowage The third system becomes more and more popular with regard to the a.m. disadvantages: the mixed stowage. Starting from the tank top you can stow from one to four tiers 20ft containers (secured only by single stacking cones) and top them up with at least on FEU. This system allows stack wise loading/discharge. The only disadvantage is that the stackweight of the TEUs is reduced a bit to about 60 ton. The new size containers make another problem. Most easily they can be stowed on deck installing additional foundations on hatch covers.

Container stowage on deck

Ship motions impose heavy loads on the deck cargo which would soon move unless secured in place. Containers carried on deck may be secured by twistlock alone. The integrity of the stow then relies on the racking strength of the containers.

Up to approx. 50t stackweight, the lowest container is able to carry the transverse and longitudinal forces on top by itself. With higher stackloads, the stack must be “ reinforced” by lashing bars: single or double cross lashings depending on the stackweight. The effectiveness of double lashings is 1.5 times that of single lashing, unless a load-equalising device is fitted. The general principle is that securing in the forward part of the ship are designed to be suitable for forces increased by 20%, unless a breakwater or similar substantial protection is fitted.

The 40ft ends have a lashing gap of minimum 700mm, so that lashing can be applied. If two 20ft containers are positioned on one 40ft place, the gap is 76mm wide and it is not possible to use lashing and the stack weight is limited to 50t. It is a rare practice to link adjacent stacks of containers. Skiiping the job substantially simplifies loading and discharging operations. It is, however, sometimes necessary to link an outboard stack to the adjacent stack to help resist wind loading. At a wind speed of 90 miles per hour, the wind force is about 2 tonnes on the side of a 20-foot box and about 4 tonnes on a 40-foot box.

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.

Container ships are likely to be driven hard in order maintain very tight operating schedules. As a consequence, thousands of containers are lost overboard every year and continue to be the source of substantial claims for P&I clubs.
Source : Wärtsilä Encyclopedia of Ship Technology




Other factors should be taken into account before accepting a containership cargo stowage plan, :


• Lashing strength

• Dangerous goods stowage and segregation

• Reefer Container Stowage

• Out of Gauge Container Stowage

• Special Container Stowage

• 20’ or 40’ or 45’ Compulsory Stowage Locations

• Irregular Stowage of Containers

• Over-stow of Containers

• Hatch Cover Clearance (High cube containers Under Deck )

• Other matters regarding cargo stowage as necessary



Back to

• General guidance for containership safe cargo stowage and planning

Stacking Weights Restrictions

Lashing strength calculation

Dangerous goods stowage and segregation

Reefer Container Stowage





Related Information:


How to load maximum number 20 feet container on deck ?

What are the extra precaution should be taken prior loading a 45 feet container on deck ?

Container damage in ''2 in 1'' cargo Operation

Modern containership & loading of various container types

How to load containers coming in different forms/sizes



Our additional pages contain somewhat larger lists of resources where you can find useful informations


Container handling more info pages:

  1. Definition of various containers in containership
    The exterior dimensions of all containers conforming to ISO standards are 20 feet long x 8 feet wide x 8 feet 6 inches high or 9 feet 6 inches high for high cube containers. Some of the most commonly used types are:Read more......


  2. Dimensions of various containers
  3. Containers are standardized cargo units. They are manufactured in a large 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.
    Read more......

  4. Containership advantages : In principle they are boxes or containers within a box. These boxes or containers have dimensions of 2.60 x 2.45 m with lengths of 6.10, 9.15 and 12.20 m. Containers are made in steel, aluminium or GRP. They are also of refrigerated design, thus advantageous for long voyages between Australia or New Zealand and the UK. Read more......


  5. Containership cargo stowage and planning : When considering acceptability of a container cargo stowage plan, the following procedures / guidelines concerning cargo stowage shall be taken into account: Stacking Weights Restrictions, Lashing strength calculation, Dangerous goods stowage and segregation, Reefer Container Stowage , Out of Gauge Container Stowage , ....Read more......


  6. DG cargo handling - IMDG code guideline :The general provisions for segregation between the various classes of dangerous goods are shown in "Segregation table" (IMDG Code Chapter 7.2.1.16). In addition to the general provisions, there may be a need to segregate a particular substance, material or article from other goods which could contribute to its hazard. Read more......


  7. How to avoid irregular stowage of containers ? Stowage plan must be checked for any irregular stowage like those mentioned here : Stacking Weights, Lashing Strength, Special Container Stowage, Over-stow of Containers, Dangerous Cargo Stowage & Segregation, 20 or 40 or 45 feet Compulsory Stowage Locations, Hatch Cover Clearance (High cube containers Under Deck ), Out of Gauge Container Stowage etc.Read more......


  8. Measures against lashing failure : Lashing strength of deck cargo shall be ascertained by using the appropriate lashing strength calculation software where provided. All resulting values for lashing strength must be within the tolerance limits prescribed by vessels classification society.Read more......


  9. Reefer container stowage guideline : Reefer containers proposed for stowage must be accompanied by a reefer manifest. This reefer manifest should contain information regarding Container No., Stow position, Commodity, Temperature and Ventilation status. Read more......


  10. Care of Reefer container during sea passage :Reefer containers require special care after they are loaded on board ship. These containers need to be supplied with power, monitored closely for proper function and repaired as required in case of malfunction. Read more......


  11. Container ships procedures for securing for sea :All movable items on deck, inside accommodation and in E/R spaces, including under-deck passages and steering flat are firmly secured. Any unsecured items, in heavy weather, risk not only being damaged themselves, but could also pose a danger to vessel safety by violent contact with sensitive equipment or fittings.Read more......


  12. Deployment and monitoring of moorings and safety of crew :The Company’s Risk Assessment procedure shall be utilized to ensure that during all anticipated mooring arrangements and equipment use, the safety of crew is ensured. Read more......


  13. Cargo securing procedure for container ship :Securing equipment will vary depending on the type of ship but is likely to include; Twistlocks Lashing bars Turnbuckles Extension hooks Stacking cones (single and double) Twist Stackers Lashing D rings Shoes/Sockets for base twistlocks ...Read more......


  14. Containership operation -Check items upon completion of repair works : As the nature of container ship operation, it’s tread to be lack of stability, due to Top Heavy Load, the Master shall always take special attention for her stability. Also the Master should remind factors to cause reducing stability more such as Alternating course with Big angle of Rudder, Towing by tugs at the scene of Berthing / Un-berthing, etc. Read more......


  15. Containership operation -Cargo ventilation requirement : Cargo holds of container ships are fitted with two basic types of ventilation systems, namely natural and mechanical. Mechanical ventilation could be of either the supply or the exhaust type. Read more......


  16. Containership operation -How to avoid wet damage ? :Water entered into vessel cargo holds may cause wet damage to the cargo inside containers especially stowed on the bottom, unless the bilge water is drained in a proper and swift manner. Read more......



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