Post-Panamax surge

The growth in containership orders and sizes of vessels appears to be relentless. There has been a flood of orders this year for new vessels, including vessels of over 8,000 TEU and Germanischer Lloyd (GL) alone claims to have 44 large container carriers of this size waiting classification. Dr. Hans Payer, executive board member for GL, believes that vessels of this size will develop into the new standard for jumbo container ships. However, he believes that the growth in size will not end there because, in addition to a 9,200 TEU design study that was completed recently, GL is also working on the design for a 12,000 TEU vessel on behalf of a shipyard.

While the order book includes more than sixty 8,000 TEU class newbuildings, Clarksons has suggested that this may not be sufficient to match projected container trade growth. Demand for cargo space is being driven by the massive increase in trade to and from China, with exports at present growing at an annualised rate of 34% and imports 46% higher in the first five months of 2003.

Studies by leading classification societies such as GL have shown that the structural requirements of container ships considerably exceeding the size of those in service or on order today can well be accommodated. The limits to the development and introduction of mega-container ships are imposed by a number of aspects such as the maximum available output of appropriate propulsion plants although systems based on single or twin prime movers and various propulsor arrangements promise efficient solutions. Other constraints include cargo handling facilities at ports and their logistics requirements and water depth of the port entrance and in harbours.

However, as the market evolves and ships up to and beyond

10,000 TEU come into service, the hatch cover is likely to come under increasing pressure. Kari Tirkkonen, senior naval architect at MacGregor, explains that the last new generation of container ship hatch covers was launched in the late 80?s when German major shipyards started to build the vessels without longitudinal girders. “This means that there is block stowage and, by partial opening, you reach as many containers in hold as you have removed from on top of the cover, which is clearly a benefit,” Tirkkonen told The Motor Ship. Those ships were still about 3,000TEU Panamax but rapidly the same concept spread to the early Post-Panamax fleet.

The growing size of vessels resulted in some interesting problems for designers. “By keeping a three-panel arrangement for each hold, the panel size was growing, giving new challenges to reliable design of bearing pads with growing relative movements as well as need for even more optimised stress analyses and structures to keep the hoisting weight down to 40 tonnes, which came as standard for 40m beam vessel hatch covers,” explains Tirkkonen. This resulted in MacGregor looking more closely at the study of vessel hull movements from the company?s various deliveries in order to be able to predict the relative movement between hatch covers and coamings and, even more important, between hatch cover and lashing bridge, the new player in deck equipment, in the design phase. “The movement related to ship period can also be used to determine the bearing pad from our wide scope of solutions, says Tirkkonen.

One of those solutions uses MacGregor?s hatch cover support technology, which utilises a range of vertical bearing pads to transfer the weight of the cover and any cargo it may be carrying to the ship?s hull while allowing for relative movement between cover and hatch coaming caused by hull flexing in a seaway. The need to develop the stress analyses further has led the company to use FEM models for all covers including fatigue calculations as necessary. Also, a new type of partial box design was developed to reduce hoisting weight since the covers are already made of 99 % hi-tensile steel and no further weight savings can be made from materials.

Tirkkonen says that a four-panel and even five-panel

solution has already been used for the 43 m beam class for the same reason.

As yards like Samsung are primed to build even larger tonnage, negotiating for 9,200 TEU vessels and having prepared plans for a twin-screw 10,000 TEU design, the loads on hatch covers are only ever likely to get higher.