Container Ship Design and Construction

Container ships are designed to carry large numbers of standard containers at high speeds between particular terminal ports and require a fast turn round at those ports. 

    The containers are loaded into the ship vertically, fitting into cell guides which are splayed out at the top to provide lead-in. 

Pads are fitted to the tank top at the bottom of the guides in line with the corner fittings. The available hold space is dictated by the size of the hatches. It is essential, therefore, to have long, wide hatches to take a maximum number of containers. 

    The spaces at the sides of the hatch are used for access and water ballast. The hatch coamings and covers are designed to carry tiers of containers as deck cargo. Since the vessels usually work between well-equipped ports, they do not usually carry their own cargo handling equipment. 

    Because of the wide hatches, the deck plating must be thick, and higher tensile steel is often used. The deck, side shell and longitudinal bulkheads are longitudinally framed in addition to the double bottom. The hatch coamings may be continuous and therefore improve the longitudinal strength. 

    Problems may arise in these vessels due to the lack of torsional strength caused by the large hatches. This problem is overcome to some extent by fitting torsion boxes on each side of the ship.

    The longitudinal bulkheads below the box may have to be stepped inboard to suit the shape of the ship, the main longitudinal bulkhead being scarphed into the stepped section. 

    At the ends of the hatches, deep box webs are fitted to increase the transverse and torsional strength of the ship. These webs are fitted at tank top and deck levels. Care is taken in the structural design at the hatch corners to avoid excessive stresses. 

The double bottom structure beneath the cell guides is subject to impact loading as the containers are put on board. Side girders are usually fitted under the container seats with additional transverse local stiffening to distribute the load.     Unlike normal cargo ships in which the cargo is distributed over the tank top, the inner bottom of a container ship is subject to point loading. The double bottom must be deep enough to support the upthrust from the water when the ship is deeply Loaded, without distortion between the container corners.

What is TEU & FEU?

What is a Torsion Box?

Bulk Carrier construction?