There are two reasons why aluminum isn't preferred as a hull material.Just wondering are there any modern classes of frigates or destroyers using aluminium for their hull construction? All I can find at the moment is LCS2.
And don't forget corrosion, especially pitting and severe issues with dissimilar metals. They work fin in the civilian and commercial world but put them in service and start pushing them and you have problems.There are two reasons why aluminum isn't preferred as a hull material.
The first reason is that aluminum warships, suffered crack from metal fatigue, the second is that should the ship burn the aluminum melts at a lower temperature and suffers structural collapse, it also conducts heat well and this helps spread the blaze.
Galvanic corrosion can be an issue with aluminium but careful construction can eliminate this type of corrosion. For naval ships steel is best but for many commercial displacement hulls, the weight savings can offer substantial fuel savings and for builders the lighter weight makes construction easier. This is why yacht builders have embraced aluminum for custom builds.And don't forget corrosion, especially pitting and severe issues with dissimilar metals. They work fin in the civilian and commercial world but put them in service and start pushing them and you have problems.
Aluminium hulls do not handle rough conditions well, well depending on hull form and active stabilisation they can perform quite well in the rough stuff but the issue is it breaks them far more quickly than it would a steel hull. For naval vessels I would pretty much always prefer smaller vessels, composite, larger ones steel and leave the aluminium to the commercial operators who know what they are doing and don't go out in the rough stuff, pleasure craft and government agency craft. Never ever for naval unless you like replacing you ships frequently and enjoy huge repair bills.Most of the cracking issues with aluminium in warships relates to mixing it with steel - they have different characteristics and the two work against each other, usually opening up cracks near where the ally meets the steel. A pure aluminium structure won't usually suffer in the same way.
As to fires, aluminium doesn't *burn* in anything like normal fire temperatures but it does lose structural strength at lower temperatures.
Extreme example, USS Belknap - but it's not every day you get run over by a carrier, showered with JP5 then set on fire.
The bonding issue with steel is vastly improved over the last decade or so.Most of the cracking issues with aluminium in warships relates to mixing it with steel - they have different characteristics and the two work against each other, usually opening up cracks near where the ally meets the steel. A pure aluminium structure won't usually suffer in the same way.
Alu still cracks when continually stressed as the RAN Armidales have shown recently and this usually results from speed and hull pounding at sea.
The OHP FFG's (and Tico's ) both suffer from deckhouse cracking due to excessive working but I read somewhere that the RAN solution was to use FRP to repair and this was reasonably successful.
As Alu ages, it tends to become brittle and also the alloy matrix begins to break down and de-laminating can be a problem.
There are many successful Alu applications but the moral of the storey is IMHO, if it floats in salt water and is bigger than a tinnie or yacht, use steel.
Chris
Galvanic corrosion can be an issue with aluminium but careful construction can eliminate this type of corrosion. For naval ships steel is best but for many commercial displacement hulls, the weight savings can offer substantial fuel savings and for builders the lighter weight makes construction easier. This is why yacht builders have embraced aluminum for custom builds.
Following the Falklands war & the loss of HMS Sheffield, the UK RN allegedly produced a report, based on technical analysis from experts & the commentary of those who survived various attacks / actions.For super yachts aluminium and composites offer a great advantage for speed and relative fuel burn as the design speed, however, the recent loss of the aluminium super yacht off cairns is a pretty good indicator of the fire resistance of such designs
Building large vessels out of aluminium poses structural challengers (by this I mean in the order of 100 m plus). If you desire the same uplift (mass) capacity life will get very interesting as you need much more structure for the same durability. Materials such as composites may resolve some of these issues but at massive cost on large platforms...... essentially this may simply not be worth it.Following the Falklands war & the loss of HMS Sheffield, the UK RN allegedly produced a report, based on technical analysis from experts & the commentary of those who survived various attacks / actions.
In the report there were several key points raised about ship design & the materials used during construction.
ONE of those was the use of Aluminium, which was 'frowned upon' in future designs, due to issues relating to a low melting point, the ability to transfer heat to adjacent spaces & starting secondary fires, listed amongst the factors.
It is always a set of scales when designing a ship as weight & structural integrity must be balanced against the speed capability of the ship, & its available space / structure to fit & support various pieces of equipment / weapons systems.
The preference in major war fighting vessels (Frigates & larger, greater than 2,500 tonnes in weight), is that while steel is heavier, the overall structural integrity & cost of the materials, mixed with thru life costs / ease of maintenance & actual life-expectancy of the material, all translate to make steel a more viable & durable option.
However, it should be noted that where 'a need for speed' is a driving factor in the capabilities of the vessel, Aluminium becomes a more attractive option, due to the weight savings that can be had.
SA
And it is also much easier to identify and monitor corrosion on steel than on aluminium., in particular when it has been painted. A painted steel structure will show rust stains where aluminium will not rather the pain will likely lift off as a sheet after the damage has been done.Building large vessels out of aluminium poses structural challengers (by this I mean in the order of 100 m plus). If you desire the same uplift (mass) capacity life will get very interesting as you need much more structure for the same durability. Materials such as composites may resolve some of these issues but at massive cost on large platforms...... essentially this may simply not be worth it.
On the commercial side A-60, A-30 and A-0 protection is very difficult on aluminium involving insulation of both sides of a bulkhead and special treatment of all penetrations. expensive and difficult. Quite often addition fixed fires systems area also required and all this adds weight and complexity.
Finally I fully agree on the durability and repair issues. Campsites would be a nightmare for you average ship yard to repair. Aluminium is common but repair has to be very careful not to build in issues as part of the process (lots of NDT please) and it is costly.
Mild steel is quite a forgiving material.