Marine aluminium in yachts and yachting has unrivalled characteristics when it comes to solidity, strength and lightness. But above all, a boat built of light alloy has practically no maintenance and boasts a much longer life cycle than other materials.
In a world like the nautical one of yachts and yachting, where the materials for the construction of boats and yachts that are all the rage are composite ones, fibreglass above all, marine aluminium might seem an obsolete material that has gone out of fashion. Actually, this is not the case and, on the contrary, aluminium alloy not only still enjoys great appreciation among yards and design studios, but in recent years this metal has experienced renewed popularity among the yachting community.
In addition to the traditional production of professional and work boats, military vessels, hydrofoils, hoovercraft and offshore speedboats, marine aluminium is often chosen for the construction of modern sailing yachts, both monohulls and multihulls, mostly dedicated to long cruises, ocean crossings and world tours. The reason for this success is very simple: aluminium boats are light, versatile and very durable. Moreover, they are perceived as sophisticated and high-tech products. Last but not least, they need very little maintenance and when it comes to life cycle and environmental sustainability, they are practically unrivalled. In this article, then, we take an in-depth look at the characteristics of marine aluminium and the advantages of a light alloy boat. We also look at some aspects related to maintenance.
The difference between aluminium and aluminium alloy
There is often confusion between aluminium and aluminium alloy because of their similar appearance and applications in adjacent sectors, such as shipbuilding or aeronautics. In reality, the two metals are very different in terms of their characteristics and properties, including their composition and processing. Let us provide some clarity!
Aluminium (Al) is a silvery-white metal with a purity level of 99 per cent or more. It is light and non-magnetic and also has a low melting point, which makes it quite malleable. But its softness is also one of the reasons why it is not durable and strong enough for most industrial applications. In its pure form, aluminium is usually used in the production of cables, cans, electronic components, foils, wires, household items and packaging materials.
Aluminium alloy, also called ‘light alloy’, is mainly obtained by combining aluminium with other metals, such as copper, zinc, silicon and magnesium. This mixture creates a material with improved properties, such as increased corrosion resistance, hardness and strength, and it is this that is used in the naval industry. An aluminium alloy has a higher melting point and more critical processing, but overall it is 30 times stronger than aluminium and even beats steel in terms of strength-to-weight ratio.
What is meant by ‘marine’ aluminium in yachts and yachting?
Let us now see exactly what type of aluminium is used to make boats and is important in yachts and yachting. When, in the mid-1960s, marine aluminium started to become popular, especially in France in the nautical sector, it was initially called ‘Duralinox’, a trade name that recalled the ‘miraculous’ qualities of stainless steel at sea. In reality, the term is somewhat deviant and it should be remembered that we are always talking about an aluminium alloy. Another widespread trade name in Italy is ‘Peralluman 4.5’, also initialled as ‘P.AlMG4.4’ according to UNI5452.
Already in 1954, the most popular and widespread light alloy in the nautical field was registered by the Alluminium Association, namely 5083, specifically designed for shipbuilding, but this abbreviation would only be used many years later with the unification of codifications and standards and the creation of the EEC (United Europe). In fact, although the acronym changed, most aluminium boats are still built with 4 or 4.5 per cent magnesium alloy.
The advantages of an aluminium boat
In addition to their great lightness, durability and solidity, aluminium boats are highly resistant to corrosion, making them ideally suited to saltwater environments. In addition, aluminium boats do not deteriorate from exposure to sunlight, which can help extend the boat’s service life. Similar resistance, such metal presents it against flames, in the event of a fire on board.
But the great strength of an aluminium boat is that it requires very little maintenance and is relatively easy to repair. In fact, marine aluminium allows itself to be mistreated, can easily withstand heavy use and hardly needs care, being far less delicate than both iron and steel.
Read the article Aluminium sailing boats: how have they changed in design? on The Marine Blog!
Galvanic corrosion: a myth to dispel
A real myth to dispel concerning aluminium boats is that hulls made from this metal suffer from electrolytic corrosion over time. The latter is due to the difference in electrical potential between the light alloy used for the hull and the various other metal components on board that are not properly insulated. In reality, a certain amount of galvanic corrosion is unavoidable, but a properly galvanically protected aluminium boat will not suffer more than superficial corrosion during its lifetime. Moreover, marine aluminium is more resistant to galvanic corrosion than other aluminium alloys.
Serious and professional builders of aluminium yachts strictly control the risk of electrolytic corrosion through a series of construction measures aimed at avoiding direct contact between the hull and metals other than sacrificial anodes. And above all through careful design of the on-board electrical system. Some aluminium yachts also often include ‘galvanic monitors’ that continuously check whether the boat is still within the intended protection range.
Here’s how to preserve your aluminium boat
A well-built marine aluminium boat does not need special care to last. There are, however, some good practices that prevent the degradation of this lightweight alloy in the long term. Winches, rigging, chains and other ferrous materials that make up the boat’s various equipment can come into direct contact with structural aluminium. Such contact can trigger the degradation of aluminium, which will naturally protect itself by producing alumina (aluminium oxide). To limit the effects of this corrosion, there are ‘Tef-Gel’ type products for contact parts. Above all, it is necessary to protect these areas from salt, air and humidity with a localised grease or paint, such as a quality two-component epoxy primer.
Other critical points are hidden board spaces, such as bilges where standing water collects, which are subject to the effects of crevice corrosion. Every so often it is a good idea to open them up, dry them out thoroughly and ventilate them. Or freshwater tanks, which trigger oxidation processes if left untreated. The main cause of this degradation is the chlorine and salt content in the water. To solve this problem, it is important to filter the fresh water with special filters. In structural water tanks, it is also essential to install magnesium anodes, which must be monitored regularly.
A long life cycle and minimal depreciation of the boat – yachts and yachting
Finally, as far as the environmental issue is concerned, a well-built metal boat lasts practically a lifetime. And this makes marine aluminium more sustainable than materials such as GRP or carbon. Moreover, light alloy boats can be easily and economically recycled at the end of their life to become other aluminium products.
Precisely because marine aluminium is easy to maintain and retains its integrity for longer, a light-alloy boat tends to retain its resale value on the second-hand market better than competing materials. If you plan to resell your boat in the future, aluminium may be the best solution.
