Not that I'd want the tail to wag the dog by building ships to keep yards open, but surely the postwar RAN was or should have been big enough to avoid the boom and bust building cycle.
I don't think so really. We seem to have averaged about a dozen or so surface combatants. If we go back to, say, the mid '80s, you had the three Perth (Charles F Adams) class destroyers, four Adelaide (Oliver Hazard Perry) class frigates, and six home-built River class destroyer escorts (the eldest, Yarra, paid off in 1985), for a surface force of 13 ships. By '95, only two of the latter were left, plus the three destroyers and six frigates (two newest ones built in Australia), for a surface force of 11 ships. At the beginning of 2005, those destroyers were all gone, so you had an all frigate force - the six Adelaides and six of the Anzacs. The last two Anzacs came at the expense of two of the Adelaides. And now, of course, we have the three Hobarts and eight Anzacs, with a plan to replace the latter with nine Hunters. Long story short, I don't see how about 12 ships is sufficient a fleet size to have an efficient-ish, sustainable naval shipbuilding industry, even allowing for the building of other vessels. I think you'd need at least 16 and preferably 18 warships to make that happen. That means you could commission a new one every 18 months or so and keep them in service for about 24-25 years. That's doable.