The latest trends in shipbuilding have become similar to those in the automobile industry in recent years and the growing demand for automobiles, heavy duty vehicles, aircraft, trains and ships is also set to significantly spur demand for aluminium flat rolled and extruded products.
Aluminium as a material in marine construction picked up in the last century due to advances in technology. Next to steel, aluminium is the most commonly used and commercially available metal. Its light weight and high strength-to-weight ratio makes it a good choice for the purpose. Aluminium alloys that generally have excellent corrosion resistance, good workability and good weldability, are often used in marine applications (marine grade aluminium).
The necessity for lowering the weight of different ships, in order to increase the payload and reduce fuel consumption, has turned shipbuilders towards aluminium alloys. Additionally, the roughly five times higher costs of Al–alloys, with respect to the costs of low-carbon steel, become acceptable if the payload increase, excellent corrosion resistance and lower maintenance costs are taken into account.
Al-alloys also directly reduce the loss of cargo dead weight due to the lighter structure of a ship while at the same time improving the ship’s stability. Moreover, by reducing the vessel’s weight, it consumes less fuel, travels longer distances and provides excellent maneuverability.
They also have superior corrosion resistance (steel corroded at a rate of 120 micrometer per year, while in a similar study, aluminium corroded at a rate of only 1 micrometer per year). Aluminium ‘s unique characteristics allow vessel volume and height to be increased without loss of stability. Large vessels can contain as much as 2,000 tonnes of aluminium. This allows for a considerable weight reduction when compared with their steel counterparts.
Substitution of aluminium for steel can result in weight savings of 35 to 45 per cent in hulls and 55 to 65 per cent in superstructures. Higher vessel speeds and load capacities can mean extra traffic volume and profit for a ship or boat operator.
These aluminium alloys are most commonly used for boat building and shipbuilding, and other marine and salt-water sensitive shore applications:
- 5052 aluminium
- 5059 aluminium
- 5083 aluminium
- 5086 aluminium
- 6061 aluminium
- 6063 aluminium
The most popular aluminium alloys for use in corrosive environments are non-heat treatable 5000, and heat-treatable 6000 type alloys, because of well-balanced strength parameters, weldabilty and formability. The 6000 alloys are stronger but two to three times less corrosion resistant than the 5000 series. The little to no need for maintenance of marine structure surfaces (less frequent painting or other coating refreshments) is an important cost saving factor during the serving of the ship – lifeline of any aluminium component.
Aluminium alloys meet or exceed the minimum yield strength requirements for normal strength steels (mild steels), and could even compete with high strength steels.
Shipbuilders such as Austal, are implementing additional improvements in the production of aluminium ships – involving router cutting, work kitting, complex extrusions and welding – that will significantly improve productivity and reduce costs in the future.
Aluminium ships have a clear advantage over steel ships with regards to total ownership costs. Aluminium ships also do not incur lifecycle maintenance costs associated with painting, and because they are generally smaller, they require less manning. And when an aluminium vessel reaches the end of its life span, it continues to provide significant benefits as a result of its high recycling value.
Aluminium-intensive cargo ships with load capacities up to 3,000 metric tonnes are under design to operate at up to 60 knots, cross the Atlantic in under 60 hours, and handle Class 6 seas.
Aluminium is recognised by and complies with the requirements of the High Speed Code of the International Maritime Organization (IMO), for vessel design, safety, and control of fire risk. The metal stands up to the torsional, flexural, compression and impact loads of high speed water travel as well as or better than steel.
With all the existing technologies and methods available for aluminium shipbuilding, aluminium has the potential to replace steel in the future as the main ship construction material.
References: Transport World Aluminium, Aluminium Insider
Sea News Feature, October 26