So it looks like your information is drawn from media reporting, and not from actual RAN information.

The LHD’s have never had seagoing issues, retention, maintenance or otherwise.

The submarines issues have been twofold, yes retention was in issue up until the mid 2000’s, but as of 2011, there are full crews. There are actually too many submariners now as we gear up for our new submarines.

The other issue was maintenance. ASC could never keep up with the maintenance schedule on top of the required upgrade schedule, mainly due to bad management and not enough facilities. These were addressed by 2012.

Currently, the RAN doesn’t have any issues putting ships to sea.

Retention is an ADF wide problem, mainly because they keep push people out on the street for stupid medical reasons, and the private sector also has a high appetite for officers, particularly operations oriented ones, particularly combat corps army officers, MWO’s and planning officers. They go from the lowest paid but highest responsibility and accountability officers in defence, to the highest paid and generally more senior people in the private sector.

Source: Am MWO in the RAN.

Now, to answer your question; generally a 1/5 of any fleet is in some form of maintenance or refit, either alongside for short cycle, or up on the blocks out of the water for deep cycle or refit. Ships are big, maintenance hungry machines. They are thousands of independent systems all connected together and they are run at 100% if capability all the time.

RAN policy is that 100% of the fleet is available in 90 days, and atleast 50% is available within 72 hours. Generally, you can put a ship to sea within 12 hours if you really need to, but it takes time to order food, store it on the ship, fuel it, finish any maintenance that is being undertaken, and recall the crew.

It’s similar for most western navies, and readiness is a constant issue for all navies, as the complexity of platforms increases.