Are there alternatives to steel ships?

The same question, but in a slightly different form, might have been asked 150-200 years ago as alternatives to wood first appeared! But while steel has had a good innings and looks set for several more decades, there are indeed alternatives emerging.

The use of aluminium, for instance, has been significant in the development of fast ferries, where strength needs to be combined with lightness. Today, large fast craft are being built of this useful material, which nevertheless does require special treatment and skilled welders able to work in aluminium. It has also been widely employed in the superstructure of cruise ships and in the construction of warships, where the need to save weight is paramount. Special aluminium alloys have also been used as cargo containment systems for the carriage of liquefied natural gas (LNG) where the cargo is carried at temperatures as low as -165deg.C and steel would be useless.

Steel continues to be used as the primary structural material, because of its availability, proven record and familiarity. Nevertheless there are steels with different properties emerging, such as those which are corrosion-resistant, high tensile and the newest of all – a specially ductile steel plate which will afford a degree of impact protection.

But are there entirely new shipbuilding materials in sight? The use of glass reinforced plastics has become widely employed in yacht building, with sizeable craft now being “moulded” in this fashion. It has been suggested that the use of composites may offer opportunities in shipbuilding, with these non-ferrous materials capable of being formulated to provide whatever characteristics are needed – ductility, flexibility, strength, rigidity, heat or cold resistance etc.

The external and re-usable fuel tanks used to launch the NASA Space Shuttles were examples of the sort of qualities composites can provide, these tanks plummeting from a great height into the sea when they were ejected from the ascending vehicle.

Here again, with composites, it has been yacht building that has tended to employ these innovative structural materials, with the qualities of lightness and strength appreciated by the designers who incorporate them. Cost, quite simply, remains a barrier to any adoption in the production of large commercial ships, with steel being the material of choice on account of its known qualities and comprehensible costs. The marine industry is not averse to innovation, but is apt to shy away from unknown structural materials and techniques proven in practice.

There has been some considerable interest in the use of polymers sandwiched between steel plates, which provide both strength and lightness in the absence of some of the stiffeners that would be otherwise required. Sandwich Plate technology, devised by the UK based Intelligent Engineering is now being employed in the reinforcement of hard working vehicle decks on ferries, while a major Korean shipbuilder is incorporating it into large vessels.
Source: BIMCO Seascapes