I am just curious to know if "Incat" and "Austal" aluminium hulls have less life that a steel hull ship?
The reason i ask is that Australia's "Armidale class" hulls are now having issues with the aluminium hulls? Would this be the same with Austal and Incat designs , a lower operating life compared to steel?
Generally yes but there a many variables to consider.
Firstly, hull thickness, the thicker the hull the greater the life. Unfortunately, if speed is a requirement, weight is critical hence lighter construction.
Secondly, alu is a "base" metal and therefore electrolysis is a huge problem if not managed and cathodic protection of the hull is paramount. This can be achieved electronically or by careful management of zinc anodes. However, strict protocols are required when managing an alu hull such as; not dropping steel objects into bilges, ensuring that no stray electrical currents are leaked into the hull, not mooring alongside steel objects for protracted periods and paying special attention to how the ship connects to shore power (this is best achieved by not having a direct connection but through induction or modulator tank.
A recent example of the differences can be seen in the USN's LCS ships. The LCS1 class are steel hulls but not very thick. The hulls have suffered quite severe cracking through hull stresses at high speed.
On the other hand. the LCS2 class experienced severe electrolysis around the jet areas aft. I suspect this is more easily managed than the former which could require extra hull stiffening hence weight.
So, in summary, for smaller vessels, hull life should be about 15 years if carefully managed. Thin steel hulls will corrode quicker, alu hulls will suffer electrolysis and possibly delaminate, ie the alu alloy will separate and become brittle.
In my world we call alu hulls "floating anodes"