Short Note on Sea Water Resistant Aluminium

Aluminium, and particularly sea water resistant aluminium is a fantastic material in a maritime environment.

Used correctly, it could benefit the customer significantly, both financially and practically.



Aluminium has only 1/3 of the net weight of steel.

Constructions in sea water resistant aluminium usually have less than half the weight of corresponding structures in steel, but has the same capacity. Difference in material qualities have been compensated for, so the structures have the same strength.

Equipment like winches and cranes are often located high in the boat, and therefore has a strong impact on stability. This often has to be compensated for by additional ballast.

The weight reduction achieved by the use of aluminium will therefore pay off doubly in the form of reduced boat weight/increased loading capacity and reduced fuel consumption, since the ballast amount also can be reduced.



The material is corrosion resistant and the need for maintenance is generally much less than for steel.

Equipment in sea water resistant aluminium can normally stand untreated on deck as long as the coupling between alu and other metals is well taken care of and corroding components are protected.

We have extensive experience in this. Varnishing of alu structures is therefore usually an aesthetic choice.


Conclusion: Low weight and low maintenance lead to reduced costs for owner/operator


Alu is significantly more expensive than steel per kilo, but only half the weight is needed and the processing is much easier. This evens out the price difference, and with reduced operation costs, it makes alu much cheaper.


Aluminium and cold. While steel can become brittle and vulnerable in deep cold, the opposite is the case for aluminium, which becomes stronger with decreasing temperatures. Structures for arctic conditions should therefore be made of sea water resistant aluminium if it is to be used in all temperature conditions.


Aesthetics. An aluminium structure does not produce rust and rust water which trickles and mars. This is important to many. Installed steel components (gear, hydraulic engines etc.) must of course be protected and maintained in the usual manner.


Question: «Is alu always best?»

Answer: «No, alu is softer than steel, so in components exposed to mechanical wear, like controls, wearing edges for wire rope guides and the like, steel is better suited. Slide bearings in alu against alu are also unsuitable. And in rough constructions where weight is insignificant and the processing degree (few hours per kg) is low, a steel construction is usually cheaper. We use other materials than alu when this is better suited.

We. e.g. use steel in some of the winch drums where weight is insignificant and hard use with rough equipment and large concentrated loads make aluminium too soft.»


Generally, the use of aluminium is increasing; both on land, sea, and air. This leads to an increasingly broader acceptance of the material, secures the second hand value and has made it easier to choose the material for decision makers who don’t possess the necessary detailed knowledge themselves.


The MBH now has more than 40 years’ experience and high competence in the construction, production and use of sea water resistant aluminium in ship equipment and hull production.

Already in the early 1970s, the management understood that aluminium was a material for the future and started to intentionally generate the necessary competence.

The first wooden boat with DnV approved alu deck was delivered in 1975, the first alu winch was delivered in 1977, and the first boat with a sea water resistant aluminium hull was delivered in 1979.


Aluminium poses other requirements to the construction and production than steel.

We consider ourselves specialists in this.

Sea water resistant aluminium is still the most important building material in our equipment production, and we are grateful for how far-seeing our management was more than 40 years ago when they decided to go for this.

The Norwegian Navy can also be grateful. In the period 1990-1995, we delivered hydraulic deck equipment for the new mine sweepers which then were built in Mandal.

Now,  about 25 years later, this equipment is still in such a good condition that the Navy now, for a fraction of the price, chooses to renovate this equipment for another 20 years instead of replacing it, and this saves them huge amounts of money.