Why choose an Aluminum Hull Sailboat for Bluewater Cruising?
For decades, aluminum has been the material of choice for building blue water cruising sailboats. It is appealing because of its strength, and therefore the safety it provides, but also because it is easy to repair and recycle. Let's take a look at the advantages of an aluminum hull sailboat, which led Allures Yachting its architect Olivier Racoupeau to make this choice from the very beginning of the project.
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Aluminum hull sailboat: safety first
The primary reason for choosing an aluminum sailing yacht for bluewater cruising is undoubtedly safety. Long passages, poorly charted areas, unexpected encounters, potentially harsh conditions, and navigating in ice all demand exceptional hull strength. The robustness of an aluminum hull provides genuine reassurance to aspiring circumnavigators.
Impact Resistance and Reinforced Protection
One of the major advantages of an aluminum hull is its ability to withstand impact. The greater ductility of aluminum allows for much greater deformation of the material before it breaks. Conversely, GRP composites are more rigid and therefore less flexible: they tear or break more suddenly in the event of impact.
Enhanced Safety when Facing the Unexpected
A sailboat with an aluminum hull therefore offers greater safety and peace of mind when faced with the possibility of unforeseen events at sea. The recent example of interactions with killer whales in the North Atlantic is very telling: the repeated movements on the rudder that they generate put sudden stress on the hull. Composite materials absorb these shocks poorly and unfortunately break or delaminate, causing leaks. On Allures ocean-going sailboats, the rudder stock tube through which the rudder stock passes through the hull is welded to the aluminum hull. The risk of damage to the hull in this area due to orcas is virtually zero.
Aluminium Thickness in Yacht Building
Aluminum alloys are classified into series according to their composition, their characteristics, and therefore their recommended uses:
- 1000 series aluminium, over 99 percent pure, is mainly used for electronics and packaging.
- 2000 series aluminium copper alloys are widely used in aeronautics.
- 5000 series (aluminium-manganese) and 6000 series (aluminium-silicon-manganese) are used in marine applications thanks to their high mechanical strength, excellent weldability, and outstanding corrosion resistance, which is essential in a marine environment.
At the French shipyard Allures Yachting, the structural elements of our monohulls (frames, stringers, bottom, reinforcements) are made from 6005, 6060, and 6082 alloys, which are very rigid, particularly in profiles. These alloys are therefore used for extruded profiles and machined parts in the structure of sailboats.
For the plating, the outer skin of the hull, the shipyard uses 5000 series alloys, which are highly ductile, as required for forming a hull without a sheer, while also offering very high mechanical strength, even when welded.
Understanding the Mechanical Strength of Aluminium
Mechanical strength is measured in megapascals (MPa). 1 MPa equals the pressure of a 10 kilogram force applied to 1 square centimetre. 250 MPa equals the pressure of 250 tonnes on 1 square metre.
However, a material's mechanical strength is not just a single number, but a set of behaviours observed under force. Among these, two key reference points are: Yield strength (Re): the limit up to which the material returns to its original shape, beyond this, permanent deformation occurs. Tensile strength or Ultimate Tensile Strength (Rm): the maximum load the material can endure before breaking, it's ultimate load.
Comparing the Mechanical Strength of Aluminum and Composite
Highly resistant, an aluminum hull is above all ductile: it dents, bends, absorbs energy, and provides visible warning signs (such as buckling).
Composite, on the other hand, reaches a sharper point of failure, with cracking or delamination and local collapse of the sandwich structure. Energy absorption depends on skin and core thickness. GRP is more rigid and therefore less flexible, tearing or breaking more abruptly on impact.
Mechanical strength values
For a hull, however, strength is not assessed by MPa alone but by the ability of a complete plate to absorb impact, a capacity influenced by thickness, shape (curvature), and internal stiffening (frames, beams, floors).
Thicker plating resists puncture better, dissipates more energy, and bends rather than tears. Mechanical loads are distributed across both the plating and the structure. Curved, stiffened hulls further multiply resistance. One of the advantages of an aluminum hull is its ability to deform rather than crack, a vital safety feature in bluewater cruising.
On Allures aluminum monohulls, depending on the model, plating thicknesses are: 8-10 mm for the bottom and immersed sections, 10-12 mm for internal reinforcements, 5-6 mm for the topsides.
With a tensile strength of over 300 MPa, more than 300 tons would need to be applied to 1 m² to cause the aluminium hull boat to break.
A Well-Designed, Well-Built Aluminium Hull Remains Light
Aluminum has a density of 2.7 g/cm3, far lower than steel (7.85) and only slightly higher than composite (1.5-2). Yet, for an equivalent structural design, aluminum hulls can be lighter than conventional GRP hulls because they do not require very thick skins or heavy reinforcements to achieve excellent strength. And this is even more true for yachts over 40 feet.
Allures sailboats combine a robust aluminum hull with a strong, lightweight composite deck. The 14 and 16 metre bluewater models from Allures Yachting therefore match the weight of similarly sized composite yachts. With hulls designed by renowned naval architect Olivier Racoupeau, Allures aluminum monohulls also deliver exceptional performance.
Discover the architect's vision in this video:
Recyclability of an Aluminum Sailboat
Beyond its strength, aluminum is a durable and recyclable material. The aluminum used by Allures Yachting is made from around 80% recycled aluminum, itself fully recyclable. When properly maintained, an aluminum hull sailboat retains its mechanical properties for decades and offers outstanding corrosion resistance, a significant advantage for environmentally conscious sailors.
The aluminum used by Allures Yachting made from 80% recycled aluminum.
Repairability anywhere in the world
Another major advantage of aluminum boat hulls is their ease of repair. Aluminum can be repaired almost anywhere, even in remote regions, without sophisticated equipment.
Any competent welder can carry out at least a temporary repair without being a marine specialist. And welders can be found all over the world. Simple, watertight aluminum patches can be welded on anywhere, keeping the voyage going.
Repairing a composite hull, by contrast, requires genuine specialists, resins, chemical catalysts, and very precise temperature and humidity conditions.
Aluminum Hull: Peace of Mind at Sea
Choosing an aluminum hull sailboat means opting for a safe, durable travelling companion, ready to face any horizon. Thanks to its remarkable impact resistance, its ability to deform without breaking, and its repairability all around the world, aluminum remains the most reliable material for sailing far and for many years.
Light, robust, recyclable, and built to last for decades, an aluminum hull boat offers unmatched peace of mind to demanding sailors.
This philosophy, focused on safety and performance, has Allures Yachting guided Allures Yachting : designing aluminum sailboats capable of taking their crews with confidence to the most ambitious destinations.
Discover all our aluminum ocean-going sailboat models: Allures 40.9 - Allures 45.9 - Allures 51.9 - Horizon 47
Frequently Asked Questions
Why is an aluminum sailboat ideal for blue water cruising
Its impact resistance provides a high level of safety and therefore greater peace of mind when blue water cruising. It can also be easily repaired anywhere in the world.
How do aluminum sailboats perform in the event of a collision?
Aluminum is on average three times stronger than composite and ductile. In the event of an impact, aluminum will absorb energy much better and may deform but will not break.
Do aluminum sailboats require special maintenance?
Aluminum sailboats simply require special attention to the life of their sacrificial anodes the proper functioning of their electrical circuit to ensure that there are no electrical leaks.
What are the differences in behavior between aluminum and composite?
Aluminum has an average tensile strength three times greater than that of composite materials. It is ductile and can withstand deformation before breaking, whereas composite materials, which have no real elastic limit, will delaminate or break suddenly upon impact.
Why choose an aluminum centerboarder sailboat centerboarder?
Due to the rigidity of its structure, an aluminum sailboat is particularly well suited for centerboarder. Installation of the system is easier and safer. And the boat can be beached more safely.
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