Not saying a composite hull is the way to go for the OPV / corvette but I should point out that far from being a structurally weak solution it is actually just about the strongest and you also don't need to worry about corrosion or fatigue. The issue it has is cost and disposal, i.e. about the only way to get rid of the hull at the end of life is to cut it up and bury it in land fill.
I also disagree on the want and need for a fully armed corvettes. Ever since the RAN retired the last of their war built corvettes and frigates there has been a recognized gap between the RANs major fleet units and patrol boats they have desired to fill. In WWII there were the Fairmile D HDMLs (Harbour Defence Motor Launch) as well as the Bathurst class corvettes which were actually designed seaward defence vessels rather than mine sweepers pressed into escort and patrol work. As these were retired the RANs Ton class mine sweepers had to step up, in particular during the Indonesian Confrontation, this was when the Attack class PBs were developed and a class of corvette planned.
The corvettes evolved, first with the addition of a helicopter, which in turn necessitated improved self defence, in the late 60s that meant Tartar and what had been a gun armed patrol vessel intended to support and free up destroyers and frigates had become the DDL light destroyer, basically a guided missile frigate, in its own right. There was still a need but scope creep had derailed the project meaning the RAN not only missed out on their corvettes but also additional high end destroyers as a simpler, less capable, Light Destroyer or FFGs, evolved from the DDL project, were procured instead. Interestingly in the late 70s it had been intended to procure a class of six gun / missile armed FAC derivatives of the Fremantle class PBs which would have to a degree filled the corvette mission but these did not proceed for cost reasons.
Since then there has been the OPC / Transfield 81m corvette (cancelled in 1996) and more recently the OCV, indefinitely deferred in 2013. To me this clearly shows there is an identified requirement otherwise it wouldn't keep reappearing, only to be cancelled and smaller less capable vessels bought instead.
Now we could build a class of OPVs which would be a massive improvement over the preceding patrol boats and able to relieve frigates in some capacities, they would still lack any real combat capability. While more durable and more effective than patrol boats they would be completely incapable of defending themselves at all meaning in any conflict they would have to be able to operate under a defensive umbrella provided by our limited number of major combatants (or allied vessels) or be left at home, they would be less effective and versatile than smaller missile armed craft used in our region. Basically once there was any degree of threat at all they would have to be left at home leaving or very limited number of major combatants to try and do everything on their own.
If we reuse the weapons, sensors and combat system from the ASMD upgraded ANZACs we could, for limited outlay, grant the RAN an additional eight warships able to do everything an OPV is intended to, even in higher threat scenarios. Instead of having to be left home, or defended, they would be able to operate independently or even add to the combat power of our major combatants. Remember, as with the cancelled DDL of the 1970s, once you add a multirole helicopter, worth tens of millions of dollars, you really need to ensure the ship can defend itself.
