The stowage on a container ship and securing arrangements

In a container ship, a stowage plan is prepared as per the container to be discharge and loaded on a particular port along with the tanks condition i.e. mass carried by the ship other than cargo. This is done to maintain the stability of the ship at all times. Chief Officer of the ship is responsible for safe and secure stowage of the cargo on ships.

Objectives when cargo is stowed in the ship 

1. To protect the ship.

2. To protect the cargo.

3. To obtain the maximum use of the available capacity of the ship.

4. To provide for rapid and systematic discharging and loading.

5. To provide for the safety of crew and shore men at all times. 

Points to remember when loading cargo container on ships: 

Over stowage should be avoided and cargo planning to be done as per the latest cargo, i.e. cargo for a later port should not be placed over that of an earlier port.

Loading conditions must be calculated for intact stability, shearing force, bending moment, torsion moment, trim and draft etc. Torsion moment, bending moment and shear force values must not exceed 100% at any time. 

The IMO visibility line should be taken care of when planning the stowage of containers on deck.

The stowage of IMDG containers to be done as per ships Document of compliance with the special requirements for ships carrying dangerous goods

The GM value is affected (increases/decreases) by means of stowing light containers on top of heavy containers respectively and vice-versa. 

GM is the also known as Metacentric height which is the distance between the centre of gravity of the ship and its metacentre. The GM is responsible for deciding the stability factor of the ship. 

In a low GM situation, it is preferable for light containers to be stowed on top. 

However, usually the GM values for ship are high and stowing light containers on top of heavy ones will only increase GM leading to a “stiff” ship with short rolling periods, which increases the stresses on the lashing. 

In this situation, it is preferable for the heavy containers to be loaded on top but with due regard to lashing stresses and staking weight. 

Cargo containers stowage is an important issue for safe shippment. So it’s nerver too trublesome to consider more and more about this issue.

Securing arrangements

1. Lashing is a general term that is used to on behalf of all the securing arrangements onboard: It includes ropes, wires, webbings, bandings, strapping or chains, bottle screws and other patent tensioning devices mostly used on container ships 

2. Tomming:  Construction of a support of square section softwood framework, which chocks off the cargo against ship’s structure or other cargo

3. Filling:  Use of air bags, empty pallets, old tyres, etc. to fill the voids and broken stowage between items of cargo and between cargo and ship’s structures 

4. Anti skid: Flat-boards are used to increase frictional capabilities of the cargoes 

5. Binding:  Even out a stow with dunnage to make several units into one block. Also stowing bags or cartons in different directions in each layer forms a self-locking slab which is a tight stow for shifting cargoes

6. Structural Modifications:  Very heavy and uncomfortably shaped cargo may be secured by welding the unit directly to the ship’s structure or by fabricating a steel framework or other support or chock which is permanently attached to the ship’s structure