Steel is a strong and durable material. However, lightweight structures offer a range of opportunities to build a green, efficient, profitable and reliable container ship at a competitive price. For Quantum, weight savings of 1,100 tonnes have been achieved by using composite structures.
Lightweight composite structures have a wide and compelling track record in weight-critical marine applications, such as high speed light crafts. They offer opportunities for not only major weight reduction but also reduced maintenance costs due to better corrosion and fatigue properties. The results of R&D projects have demonstrated that weight savings of 30–70% can be achieved with lightweight composites compared to traditional steel structures.
Until recently, the SOLAS regulations required load-bearing structures to be made of non-combustible materials. However, a recent amendment to these regulations now allows the use of composite materials provided that adequate safety is demonstrated by a risk assessment and a fire engineering analysis.
Weight saving in Quantum
For Quantum, a study was first carried out to screen the potential application areas in order to estimate the weight reduction potential and acquisition cost and identify the most promising solutions. The focus was then put on the superstructure, piping and hatch covers based on feasibility and potential. The results of the study showed that, by using a glass fibre reinforced plastic (GFRP) composite sandwich construction, a significant weight reduction in the range of tonnes 1,100 can be achieved by only focusing on these items.
The use of 1,200 FEU reefers is another area with opportunities, where increased volume capacity, weight saving and a reduction in the power used by cooling units can be achieved. Foam core sandwich structures offer the additional benefits of an integrated insulating function in addition to stiffness and an improved strength to weight ratio. The weight saving potential is estimated to be about 2,000 tonnes compared to a traditional steel design for 1,200 TEU reefers.
Weight reduction could be directly turned into financial benefits in two different ways: to reduce fuel consumption and CO2 emissions and/or to increase the service speed and operation range. The reduction in fuel consumption was estimated to be in the order of 1–3.5% based on weight savings of 2,000–5,000 tonnes.
Other benefits FRP materials are subject to little or no corrosion if used properly. Such materials are virtually maintenance-free, producing low running costs. Stress concentrations are less critical than with metals, hence fatigue cracking is less of a problem. For instance, it is estimated that the fatigue life of composite piping in seawater is 20 years compared to seven for steel piping.
Two of Quantum’s special features are the large wind deflector and wave breaker located in the fore. Both components are to be built in GFRP because of this material’s low weight and superior corrosion resistance and the ease with which it can be formed into complex shapes.
Costs
The cost of materials for a lightweight structure is higher than for an equivalent steel structure. However, building large quantities for large structures produces lower prices. Studies of FRP marine structures show that the total cost (materials, fabrication, finishing and installation) varies from about 0.6 to 2 times the cost of an equivalent steel structure. The operating cost is assumed to be lower than that of a traditional steel structure. Hence, a small initial investment of a few per cent of the construction costs may yield significant lifecycle savings. Whether or not a lightweight construction is commercially attractive depends largely on the intended trade and how those new benefits are capitalised on.
Recycling
The recycling of composite materials is becoming an important topic as the volume of composite used in the world is growing fast. No universal solution for recycling composite materials has yet been found. Nevertheless, there are a number of promising technologies that have been and are being tested with two kinds of valorisation: thermal and material.
Sandwich Structure
A structural sandwich is a special form of a laminated composite comprising of a combination of different materials that are bonded to each other so as to utilise the properties of each separate component to the structural advantage of the whole assembly.
Composite Sandwich Structure 
Typical materials
Face Materials:
Fibre-reinforced plastics laminates, e.g. glass fibre and epoxy resin
Metal sheet
Core Materials:
Foam
Balsa wood
Elastomer
Honeycomb
Key properties
High stiffness to weight ratio
High strength to weight ratio
Good fatigue and corrosion properties
Designer Flexibility
Properties can be tailored
High margin against catastrophic failure
Dampening of noise and vibration
Improved thermal insulation