Understand what you mean… I just think 40% might be on the high side given the defence systems…radar, weapons would be the same and from posts here that makes up about 50% of the ship eventual costs.In the scenario being proposed (5 - 6 vessels each from 2 completely different countries and shipbuilders) you end up having to run 2 completely separate supply chains, with corresponding smaller populations of parts. This results in a smaller population of parts over which to distribute the originators profit. Also there is the increased administrative cost from running 2 separate sustainment processes.
Also to migrate to a common supply chain would require each of the shipbuilders as the Design Authority to give their approval of each Australian sourced replacement part. This would not be a quick and easy process dealing with 2 separate entities (it is hard enough even dealing with a single DA).
Then there is the need for 2 separate training streams, plus the separate manning management issues that would arise. All of which have costs that add up over the life of the platforms.
My thoughts are get 3 each off shore. this solves the critical timing issue where but the early 30s we don’t have enough ships. Build the balance here and to avoid a valley of death keep start to sell them once the final oz build is delivered and keep the building going with future updates as the industry here matures.